scx_bpf_dsq_reenq() currently only supports local DSQs. Extend it to support
user-defined DSQs by adding a deferred re-enqueue mechanism similar to the
local DSQ handling.
Add per-cpu deferred_reenq_user_node/flags to scx_dsq_pcpu and
deferred_reenq_users list to scx_rq. When scx_bpf_dsq_reenq() is called on a
user DSQ, the DSQ's per-cpu node is added to the current rq's deferred list.
process_deferred_reenq_users() then iterates the DSQ using the cursor helpers
and re-enqueues each task.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Factor out cursor-based DSQ iteration from bpf_iter_scx_dsq_next() into
nldsq_cursor_next_task() and the task-lost check from scx_dsq_move() into
nldsq_cursor_lost_task() to prepare for reuse.
As ->priv is only used to record dsq->seq for cursors, update
INIT_DSQ_LIST_CURSOR() to take the DSQ pointer and set ->priv from dsq->seq
so that users don't have to read it manually. Move scx_dsq_iter_flags enum
earlier so nldsq_cursor_next_task() can use SCX_DSQ_ITER_REV.
bypass_lb_cpu() now sets cursor.priv to dsq->seq but doesn't use it.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Add per-CPU data structure to dispatch queues. Each DSQ now has a percpu
scx_dsq_pcpu which contains a back-pointer to the DSQ. This will be used by
future changes to implement per-CPU reenqueue tracking for user DSQs.
init_dsq() now allocates the percpu data and can fail, so it returns an
error code. All callers are updated to handle failures. exit_dsq() is added
to free the percpu data and is called from all DSQ cleanup paths.
In scx_bpf_create_dsq(), init_dsq() is called before rcu_read_lock() since
alloc_percpu() requires GFP_KERNEL context, and dsq->sched is set
afterwards.
v2: Fix err_free_pcpu to only exit_dsq() initialized bypass DSQs (Andrea
Righi).
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Add infrastructure to pass flags through the deferred reenqueue path.
reenq_local() now takes a reenq_flags parameter, and scx_sched_pcpu gains a
deferred_reenq_local_flags field to accumulate flags from multiple
scx_bpf_dsq_reenq() calls before processing. No flags are defined yet.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
scx_bpf_reenqueue_local() can only trigger re-enqueue of the current CPU's
local DSQ. Introduce scx_bpf_dsq_reenq() which takes a DSQ ID and can target
any local DSQ including remote CPUs via SCX_DSQ_LOCAL_ON | cpu. This will be
expanded to support user DSQs by future changes.
scx_bpf_reenqueue_local() is reimplemented as a simple wrapper around
scx_bpf_dsq_reenq(SCX_DSQ_LOCAL, 0) and may be deprecated in the future.
Update compat.bpf.h with a compatibility shim and scx_qmap to test the new
functionality.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Wrap the deferred_reenq_local_node list_head into struct
scx_deferred_reenq_local. More fields will be added and this allows using a
shorthand pointer to access them.
No functional change.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
The deferred reenqueue local mechanism uses an llist (lockless list) for
collecting schedulers that need their local DSQs re-enqueued. Convert to a
regular list protected by a raw_spinlock.
The llist was used for its lockless properties, but the upcoming changes to
support remote reenqueue require more complex list operations that are
difficult to implement correctly with lockless data structures. A spinlock-
protected regular list provides the necessary flexibility.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Previously, both process_ddsp_deferred_locals() and reenq_local() required
forward declarations. Reorganize so that only run_deferred() needs to be
declared. Both callees are grouped right before run_deferred() for better
locality. This reduces forward declaration clutter and will ease adding more
to the run_deferred() path.
No functional changes.
v2: Also relocate process_ddsp_deferred_locals() next to run_deferred()
(Daniel Jordan).
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Change find_global_dsq() to take a CPU number directly instead of a task
pointer. This prepares for callers where the CPU is available but the task is
not.
No functional changes.
v2: Rename tcpu to cpu in find_global_dsq() (Emil Tsalapatis).
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Extract pnode allocation and deallocation logic into alloc_pnode() and
free_pnode() helpers. This simplifies scx_alloc_and_add_sched() and prepares
for adding more per-node initialization and cleanup in subsequent patches.
No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Global DSQs are currently stored as an array of scx_dispatch_q pointers,
one per NUMA node. To allow adding more per-node data structures, wrap the
global DSQ in scx_sched_pnode and replace global_dsqs with pnode array.
NUMA-aware allocation is maintained. No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Move scx_bpf_task_cgroup() kfunc definition and its BTF_ID entry to the end
of the kfunc section before __bpf_kfunc_end_defs() for cleaner code
organization.
No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
ops.quiescent() is invoked with the same deq_flags as ops.dequeue(), so
the BPF scheduler is able to distinguish sleep vs property changes in
both callbacks.
However, dequeue_task_scx() receives deq_flags as an int from the
sched_class interface, so SCX flags above bit 32 (%SCX_DEQ_SCHED_CHANGE)
are truncated. ops_dequeue() reconstructs the full u64 for ops.dequeue(),
but ops.quiescent() is still called with the original int and can never
see %SCX_DEQ_SCHED_CHANGE.
Fix this by constructing the full u64 deq_flags in dequeue_task_scx()
(renaming the int parameter to core_deq_flags) and passing the complete
flags to both ops_dequeue() and ops.quiescent().
Fixes: ebf1ccff79 ("sched_ext: Fix ops.dequeue() semantics")
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
enqueue_task_scx() takes int enq_flags from the sched_class interface.
SCX enqueue flags starting at bit 32 (SCX_ENQ_PREEMPT and above) are
silently truncated when passed through activate_task(). extra_enq_flags
was added as a workaround - storing high bits in rq->scx.extra_enq_flags
and OR-ing them back in enqueue_task_scx(). However, the OR target is
still the int parameter, so the high bits are lost anyway.
The current impact is limited as the only affected flag is SCX_ENQ_PREEMPT
which is informational to the BPF scheduler - its loss means the scheduler
doesn't know about preemption but doesn't cause incorrect behavior.
Fix by renaming the int parameter to core_enq_flags and introducing a
u64 enq_flags local that merges both sources. All downstream functions
already take u64 enq_flags.
Fixes: f0e1a0643a ("sched_ext: Implement BPF extensible scheduler class")
Cc: stable@vger.kernel.org # v6.12+
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This is an early-stage partial implementation that demonstrates the core
building blocks for nested sub-scheduler dispatching. While significant
work remains in the enqueue path and other areas, this patch establishes
the fundamental mechanisms needed for hierarchical scheduler operation.
The key building blocks introduced include:
- Private stack support for ops.dispatch() to prevent stack overflow when
walking down nested schedulers during dispatch operations
- scx_bpf_sub_dispatch() kfunc that allows parent schedulers to trigger
dispatch operations on their direct child schedulers
- Proper parent-child relationship validation to ensure dispatch requests
are only made to legitimate child schedulers
- Updated scx_dispatch_sched() to handle both nested and non-nested
invocations with appropriate kf_mask handling
The qmap scheduler is updated to demonstrate the functionality by calling
scx_bpf_sub_dispatch() on registered child schedulers when it has no
tasks in its own queues.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Add rhashtable-based lookup for sub-schedulers indexed by cgroup_id to
enable efficient scheduler discovery in preparation for multiple scheduler
support. The hash table allows quick lookup of the appropriate scheduler
instance when processing tasks from different cgroups.
This extends scx_link_sched() to register sub-schedulers in the hash table
and scx_unlink_sched() to remove them. A new scx_find_sub_sched() function
provides the lookup interface.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Factor out scx_link_sched() and scx_unlink_sched() functions to reduce
code duplication in the scheduler enable/disable paths.
No functional change.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
scx_bpf_reenqueue_local() currently re-enqueues all tasks on the local DSQ
regardless of which sub-scheduler owns them. With multiple sub-schedulers,
each should only re-enqueue tasks it owns or are owned by its descendants.
Replace the per-rq boolean flag with a lock-free linked list to track
per-scheduler reenqueue requests. Filter tasks in reenq_local() using
hierarchical ownership checks and block deferrals during bypass to prevent
use on dead schedulers.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Add a back pointer from scx_sched_pcpu to scx_sched. This will be used by
the next patch to make scx_bpf_reenqueue_local() sub-sched aware.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
The preceding changes implemented the framework to support cgroup
sub-scheds and updated scheduling paths and kfuncs so that they have
minimal but working support for sub-scheds. However, actual sub-sched
enabling/disabling hasn't been implemented yet and all tasks stayed on
scx_root.
Implement cgroup sub-sched enabling and disabling to actually activate
sub-scheds:
- Both enable and disable operations bypass only the tasks in the subtree
of the child being enabled or disabled to limit disruptions.
- When enabling, all candidate tasks are first initialized for the child
sched. Once that succeeds, the tasks are exited for the parent and then
switched over to the child. This adds a bit of complication but
guarantees that child scheduler failures are always contained.
- Disabling works the same way in the other direction. However, when the
parent may fail to initialize a task, disabling is propagated up to the
parent. While this means that a parent sched fail due to a child sched
event, the failure can only originate from the parent itself (its
ops.init_task()). The only effect a malfunctioning child can have on the
parent is attempting to move the tasks back to the parent.
After this change, although not all the necessary mechanisms are in place
yet, sub-scheds can take control of their tasks and schedule them.
v2: Fix missing scx_cgroup_unlock()/percpu_up_write() in abort path
(Cheng-Yang Chou).
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Extend scx_dump_state() to support multiple schedulers and improve task
identification in dumps. The function now takes a specific scheduler to
dump and can optionally filter tasks by scheduler.
scx_dump_task() now displays which scheduler each task belongs to, using
"*" to mark tasks owned by the scheduler being dumped. Sub-schedulers
are identified with their level and cgroup ID.
The SysRq-D handler now iterates through all active schedulers under
scx_sched_lock and dumps each one separately. For SysRq-D dumps, only
tasks owned by each scheduler are dumped to avoid redundancy since all
schedulers are being dumped. Error-triggered dumps continue to dump all
tasks since only that specific scheduler is being dumped.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
The scx_dump_state() function uses a regular spinlock to serialize
access. In a subsequent patch, this function will be called while
holding scx_sched_lock, which is a raw spinlock, creating a lock
nesting violation.
Convert the dump_lock to a raw spinlock and use the guard macro for
cleaner lock management.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Currently, the watchdog checks all tasks as if they are all on scx_root.
Move scx_watchdog_timeout inside scx_sched and make check_rq_for_timeouts()
use the timeout from the scx_sched associated with each task.
refresh_watchdog() is added, which determines the timer interval as half of
the shortest watchdog timeouts of all scheds and arms or disarms it as
necessary. Every scx_sched instance has equivalent or better detection
latency while sharing the same timer.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
scx_dsp_ctx and scx_dsp_max_batch are global variables used in the dispatch
path. In prepration for multiple scheduler support, move the former into
scx_sched_pcpu and the latter into scx_sched. No user-visible behavior
changes intended.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
The cgroup sub-sched support involves invasive changes to many areas of
sched_ext. The overall scaffolding is now in place and the next step is
implementing sub-sched enable/disable.
To enable partial testing and verification, update balance_one() to
dispatch from all scx_sched instances until it finds a task to run. This
should keep scheduling working when sub-scheds are enabled with tasks on
them. This will be replaced by BPF-driven hierarchical operation.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
When a sub-scheduler enters bypass mode, its tasks must be scheduled by an
ancestor to guarantee forward progress. Tasks from bypassing descendants are
queued in the bypass DSQs of the nearest non-bypassing ancestor, or the root
scheduler if all ancestors are bypassing. This requires coordination between
bypassing schedulers and their hosts.
Add bypass_enq_target_dsq() to find the correct bypass DSQ by walking up the
hierarchy until reaching a non-bypassing ancestor. When a sub-scheduler starts
bypassing, all its runnable tasks are re-enqueued after scx_bypassing() is set,
ensuring proper migration to ancestor bypass DSQs.
Update scx_dispatch_sched() to handle hosting bypassed descendants. When a
scheduler is not bypassing but has bypassing descendants, it must schedule both
its own tasks and bypassed descendant tasks. A simple policy is implemented
where every Nth dispatch attempt (SCX_BYPASS_HOST_NTH=2) consumes from the
bypass DSQ. A fallback consumption is also added at the end of dispatch to
ensure bypassed tasks make progress even when normal scheduling is idle.
Update enable_bypass_dsp() and disable_bypass_dsp() to increment
bypass_dsp_enable_depth on both the bypassing scheduler and its parent host,
ensuring both can detect that bypass dispatch is active through
bypass_dsp_enabled().
Add SCX_EV_SUB_BYPASS_DISPATCH event counter to track scheduling of bypassed
descendant tasks.
v2: Fix comment typos (Andrea).
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
The bypass_depth field tracks nesting of bypass operations but is also used
to determine whether the bypass dispatch path should be active. With
hierarchical scheduling, child schedulers may need to activate their parent's
bypass dispatch path without affecting the parent's bypass_depth, requiring
separation of these concerns.
Add bypass_dsp_enable_depth and bypass_dsp_claim to independently control
bypass dispatch path activation. The new enable_bypass_dsp() and
disable_bypass_dsp() functions manage this state with proper claim semantics
to prevent races. The bypass dispatch path now only activates when
bypass_dsp_enabled() returns true, which checks the new enable_depth counter.
The disable operation is carefully ordered after all tasks are moved out of
bypass DSQs to ensure they are drained before the dispatch path is disabled.
During scheduler teardown, disable_bypass_dsp() is called explicitly to ensure
cleanup even if bypass mode was never entered normally.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
The @prev parameter passed into ops.dispatch() is expected to be on the
same sched. Passing in @prev which isn't on the sched can spuriously
trigger failures that can kill the scheduler. Pass in @prev iff it's on
the same sched.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
In preparation of multiple scheduler support, factor out
scx_dispatch_sched() from balance_one(). The function boundary makes
remembering $prev_on_scx and $prev_on_rq less useful. Open code $prev_on_scx
in balance_one() and $prev_on_rq in both balance_one() and
scx_dispatch_sched().
No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Bypass mode is used to simplify enable and disable paths and guarantee
forward progress when something goes wrong. When enabled, all tasks skip BPF
scheduling and fall back to simple in-kernel FIFO scheduling. While this
global behavior can be used as-is when dealing with sub-scheds, that would
allow any sub-sched instance to affect the whole system in a significantly
disruptive manner.
Make bypass state hierarchical by propagating it to descendants and updating
per-cpu flags accordingly. This allows an scx_sched to bypass if itself or
any of its ancestors are in bypass mode. However, this doesn't make the
actual bypass enqueue and dispatch paths hierarchical yet. That will be done
in later patches.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
In preparation of multiple scheduler support, make bypass state
per-scx_sched. Move scx_bypass_depth, bypass_timestamp and bypass_lb_timer
from globals into scx_sched. Move SCX_RQ_BYPASSING from rq to scx_sched_pcpu
as SCX_SCHED_PCPU_BYPASSING.
scx_bypass() now takes @sch and scx_rq_bypassing(rq) is replaced with
scx_bypassing(sch, cpu). All callers updated.
scx_bypassed_for_enable existed to balance the global scx_bypass_depth when
enable failed. Now that bypass_depth is per-scheduler, the counter is
destroyed along with the scheduler on enable failure. Remove
scx_bypassed_for_enable.
As all tasks currently use the root scheduler, there's no observable behavior
change.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
To support bypass mode for sub-schedulers, move bypass_dsq from struct scx_rq
to struct scx_sched_pcpu. Add bypass_dsq() helper. Move bypass_dsq
initialization from init_sched_ext_class() to scx_alloc_and_attach_sched().
bypass_lb_cpu() now takes a CPU number instead of rq pointer. All callers
updated. No behavior change as all tasks use the root scheduler.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
The abort state was tracked in the global scx_aborting flag which was used to
break out of potential live-lock scenarios when an error occurs. With
hierarchical scheduling, each scheduler instance must track its own abort
state independently so that an aborting scheduler doesn't interfere with
others.
Move the aborting flag into struct scx_sched and update all access sites. The
early initialization check in scx_root_enable() that warned about residual
aborting state is no longer needed as each scheduler instance now starts with
a clean state.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
The default time slice was stored in the global scx_slice_dfl variable which
was dynamically modified when entering and exiting bypass mode. With
hierarchical scheduling, each scheduler instance needs its own default slice
configuration so that bypass operations on one scheduler don't affect others.
Move slice_dfl into struct scx_sched and update all access sites. The bypass
logic now modifies the root scheduler's slice_dfl. At task initialization in
init_scx_entity(), use the SCX_SLICE_DFL constant directly since the task may
not yet be associated with a specific scheduler.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Call ops.core_sched_before() iff both tasks belong to the same scx_sched.
Otherwise, use timestamp based ordering.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
- Add the @sch parameter to scx_init_task() and drop @tg as it can be
obtained from @p. Separate out __scx_init_task() which does everything
except for the task state transition.
- Add the @sch parameter to scx_enable_task(). Separate out
__scx_enable_task() which does everything except for the task state
transition.
- Add the @sch parameter to scx_disable_task().
- Rename scx_exit_task() to scx_disable_and_exit_task() and separate out
__scx_disable_and_exit_task() which does everything except for the task
state transition.
While some task state transitions are relocated, no meaningful behavior
changes are expected.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
scx_bpf_dsq_move[_vtime]() calls scx_dsq_move() to move task from a DSQ to
another. However, @p doesn't necessarily have to come form the containing
iteration and can thus be a task which belongs to another scx_sched. Verify
that @p is on the same scx_sched as the DSQ being iterated.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
scx_bpf_task_set_slice() and scx_bpf_task_set_dsq_vtime() now verify that
the calling scheduler has authority over the task before allowing updates.
This prevents schedulers from modifying tasks that don't belong to them in
hierarchical scheduling configurations.
Direct writes to p->scx.slice and p->scx.dsq_vtime are deprecated and now
trigger warnings. They will be disallowed in a future release.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Add checks to enforce scheduling authority boundaries when multiple
schedulers are present:
1. In scx_dsq_insert_preamble() and the dispatch retry path, ignore attempts
to insert tasks that the scheduler doesn't own, counting them via
SCX_EV_INSERT_NOT_OWNED. As BPF schedulers are allowed to ignore
dequeues, such attempts can occur legitimately during sub-scheduler
enabling when tasks move between schedulers. The counter helps distinguish
normal cases from scheduler bugs.
2. For scx_bpf_dsq_insert_vtime() and scx_bpf_select_cpu_and(), error out
when sub-schedulers are attached. These functions lack the aux__prog
parameter needed to identify the calling scheduler, so they cannot be used
safely with multiple schedulers. BPF programs should use the arg-wrapped
versions (__scx_bpf_dsq_insert_vtime() and __scx_bpf_select_cpu_and())
instead.
These checks ensure that with multiple concurrent schedulers, scheduler
identity can be properly determined and unauthorized task operations are
prevented or tracked.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
In preparation for multiple scheduler support, introduce scx_prog_sched()
accessor which returns the scx_sched instance associated with a BPF program.
The association is determined via the special KF_IMPLICIT_ARGS kfunc
parameter, which provides access to bpf_prog_aux. This aux can be used to
retrieve the struct_ops (sched_ext_ops) that the program is associated with,
and from there, the corresponding scx_sched instance.
For compatibility, when ops.sub_attach is not implemented (older schedulers
without sub-scheduler support), unassociated programs fall back to scx_root.
A warning is logged once per scheduler for such programs.
As scx_root is still the only scheduler, this shouldn't introduce
user-visible behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
In preparation of multiple scheduler support, add p->scx.sched which points
to the scx_sched instance that the task is scheduled by, which is currently
always scx_root. Add scx_task_sched[_rcu]() accessors which return the
associated scx_sched of the specified task and replace the raw scx_root
dereferences with it where applicable. scx_task_on_sched() is also added to
test whether a given task is on the specified sched.
As scx_root is still the only scheduler, this shouldn't introduce
user-visible behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
A system often runs multiple workloads especially in multi-tenant server
environments where a system is split into partitions servicing separate
more-or-less independent workloads each requiring an application-specific
scheduler. To support such and other use cases, sched_ext is in the process
of growing multiple scheduler support.
When partitioning a system in terms of CPUs for such use cases, an
oft-taken approach is hard partitioning the system using cpuset. While it
would be possible to tie sched_ext multiple scheduler support to cpuset
partitions, such an approach would have fundamental limitations stemming
from the lack of dynamism and flexibility.
Users often don't care which specific CPUs are assigned to which workload
and want to take advantage of optimizations which are enabled by running
workloads on a larger machine - e.g. opportunistic over-commit, improving
latency critical workload characteristics while maintaining bandwidth
fairness, employing control mechanisms based on different criteria than
on-CPU time for e.g. flexible memory bandwidth isolation, packing similar
parts from different workloads on same L3s to improve cache efficiency,
and so on.
As this sort of dynamic behaviors are impossible or difficult to implement
with hard partitioning, sched_ext is implementing cgroup sub-sched support
where schedulers can be attached to the cgroup hierarchy and a parent
scheduler is responsible for controlling the CPUs that each child can use
at any given moment. This makes CPU distribution dynamically controlled by
BPF allowing high flexibility.
This patch adds the skeletal sched_ext cgroup sub-sched support:
- sched_ext_ops.sub_cgroup_id and .sub_attach/detach() are added. Non-zero
sub_cgroup_id indicates that the scheduler is to be attached to the
identified cgroup. A sub-sched is attached to the cgroup iff the nearest
ancestor scheduler implements .sub_attach() and grants the attachment. Max
nesting depth is limited by SCX_SUB_MAX_DEPTH.
- When a scheduler exits, all its descendant schedulers are exited
together. Also, cgroup.scx_sched added which points to the effective
scheduler instance for the cgroup. This is updated on scheduler
init/exit and inherited on cgroup online. When a cgroup is offlined, the
attached scheduler is automatically exited.
- Sub-sched support is gated on CONFIG_EXT_SUB_SCHED which is
automatically enabled if both SCX and cgroups are enabled. Sub-sched
support is not tied to the CPU controller but rather the cgroup
hierarchy itself. This is intentional as the support for cpu.weight and
cpu.max based resource control is orthogonal to sub-sched support. Note
that CONFIG_CGROUPS around cgroup subtree iteration support for
scx_task_iter is replaced with CONFIG_EXT_SUB_SCHED for consistency.
- This allows loading sub-scheds and most framework operations such as
propagating disable down the hierarchy work. However, sub-scheds are not
operational yet and all tasks stay with the root sched. This will serve
as the basis for building up full sub-sched support.
- DSQs point to the scx_sched they belong to.
- scx_qmap is updated to allow attachment of sub-scheds and also serving
as sub-scheds.
- scx_is_descendant() is added but not yet used in this patch. It is used by
later changes in the series and placed here as this is where the function
belongs.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
In preparation for multiple scheduler support, reorganize the enable and
disable paths to make scheduler instances explicit. Extract
scx_root_disable() from scx_disable_workfn(). Rename scx_enable_workfn()
to scx_root_enable_workfn(). Change scx_disable() to take @sch parameter
and only queue disable_work if scx_claim_exit() succeeds for consistency.
Move exit_kind validation into scx_claim_exit(). The sysrq handler now
prints a message when no scheduler is loaded.
These changes don't materially affect user-visible behavior.
v2: Keep scx_enable() name as-is and only rename the workfn to
scx_root_enable_workfn(). Change scx_enable() return type to s32.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
- Always trigger the warning if p->scx.disallow is set for fork inits. There
is no reason to set it during forks.
- Flip the positions of if/else arms to ease adding error conditions.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Make sched_cgroup_fork() pass @kargs to scx_fork(). This will be used to
determine @p's cgroup for cgroup sub-sched support.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Cc: Peter Zijlstra <peterz@infradead.org>
For the planned cgroup sub-scheduler support, enable/disable operations are
going to be subtree specific and iterating all tasks in the system for those
operations can be unnecessarily expensive and disruptive.
cgroup already has mechanisms to perform subtree task iterations. Implement
cgroup subtree iteration for scx_task_iter:
- Add optional @cgrp to scx_task_iter_start() which enables cgroup subtree
iteration.
- Make scx_task_iter use css_next_descendant_pre() and css_task_iter to
iterate all tasks in the cgroup subtree.
- Update all existing callers to pass NULL to maintain current behavior.
The two iteration mechanisms are independent and duplicate. It's likely that
scx_tasks can be removed in favor of always using cgroup iteration if
CONFIG_SCHED_CLASS_EXT depends on CONFIG_CGROUPS.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Commit 0927780c90 ("sched_ext: Use READ_ONCE() for lock-free reads
of module param variables") annotated the plain reads of
scx_slice_bypass_us and scx_bypass_lb_intv_us in bypass_lb_cpu(), but
missed a third site in scx_bypass():
WRITE_ONCE(scx_slice_dfl, scx_slice_bypass_us * NSEC_PER_USEC);
scx_slice_bypass_us is a module parameter writable via sysfs in
process context through set_slice_us() -> param_set_uint_minmax(),
which performs a plain store without holding bypass_lock. scx_bypass()
reads the variable under bypass_lock, but since the writer does not
take that lock, the two accesses are concurrent.
WRITE_ONCE() only applies volatile semantics to the store of
scx_slice_dfl -- the val expression containing scx_slice_bypass_us is
evaluated as a plain read, providing no protection against concurrent
writes.
Wrap the read with READ_ONCE() to complete the annotation started by
commit 0927780c90 and make the access KCSAN-clean, consistent with
the existing READ_ONCE(scx_slice_bypass_us) in bypass_lb_cpu().
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
raw_spin_rq_unlock() is short, and is called in some hot code paths
such as finish_lock_switch().
Inline raw_spin_rq_unlock() to micro-optimize performance a bit.
Signed-off-by: Xie Yuanbin <qq570070308@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20260216164950.147617-3-qq570070308@gmail.com
This recent commit:
96d1610e0b ("sched: Optimize hrtimer handling")
introduced a new build warning when !CONFIG_HOTPLUG_CPU
while SCHED_HRTIMERS=y [ == HIGH_RES_TIMERS=y ]:
/tip.testing/kernel/sched/core.c:882:13: warning: ‘hrtick_clear’ defined but not used [-Wunused-function]
Mark this helper function as always-used, instead of complicating
the code with another obscure #ifdef.
Fixes: 96d1610e0b ("sched: Optimize hrtimer handling")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/177245077226.1647592.1821545206171336606.tip-bot2@tip-bot2
The task ownership state machine in sched_ext is quite hard to follow
from the code alone. The interaction of ownership states, memory
ordering rules and cross-CPU "lock dancing" makes the overall model
subtle.
Extend the documentation next to scx_ops_state to provide a more
structured and self-contained description of the state transitions and
their synchronization rules.
The new reference should make the code easier to reason about and
maintain and can help future contributors understand the overall
task-ownership workflow.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
bypass_lb_cpu() reads scx_bypass_lb_intv_us and scx_slice_bypass_us
without holding any lock, in timer callback context where module
parameter writes via sysfs can happen concurrently:
min_delta_us = scx_bypass_lb_intv_us / SCX_BYPASS_LB_MIN_DELTA_DIV;
^^^^^^^^^^^^^^^^^^^^
plain read -- KCSAN data race
if (delta < DIV_ROUND_UP(min_delta_us, scx_slice_bypass_us))
^^^^^^^^^^^^^^^^^
plain read -- KCSAN data race
scx_bypass_lb_intv_us already uses READ_ONCE() in scx_bypass_lb_timerfn()
and scx_bypass() for its other lock-free read sites, leaving
bypass_lb_cpu() inconsistent. scx_slice_bypass_us has the same
lock-free access pattern in the same function.
Fix both plain reads by using READ_ONCE() to complete the concurrent
access annotation and make the code KCSAN-clean.
Signed-off-by: zhidao su <suzhidao@xiaomi.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
bpf_iter_scx_dsq_new() reads dsq->seq via READ_ONCE() without holding
any lock, making dsq->seq a lock-free concurrently accessed variable.
However, dispatch_enqueue(), the sole writer of dsq->seq, uses a plain
increment without the matching WRITE_ONCE() on the write side:
dsq->seq++;
^^^^^^^^^^^
plain write -- KCSAN data race
The KCSAN documentation requires that if one accessor uses READ_ONCE()
or WRITE_ONCE() on a variable to annotate lock-free access, all other
accesses must also use the appropriate accessor. A plain write leaves
the pair incomplete and will trigger KCSAN warnings.
Fix by using WRITE_ONCE() for the write side of the update:
WRITE_ONCE(dsq->seq, dsq->seq + 1);
This is consistent with bpf_iter_scx_dsq_new() and makes the
concurrent access annotation complete and KCSAN-clean.
Signed-off-by: zhidao su <suzhidao@xiaomi.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Running stress-ng --schedpolicy 0 on an RT kernel on a big machine
might lead to the following WARNINGs (edited).
sched: DL de-boosted task PID 22725: REPLENISH flag missing
WARNING: CPU: 93 PID: 0 at kernel/sched/deadline.c:239 dequeue_task_dl+0x15c/0x1f8
... (running_bw underflow)
Call trace:
dequeue_task_dl+0x15c/0x1f8 (P)
dequeue_task+0x80/0x168
deactivate_task+0x24/0x50
push_dl_task+0x264/0x2e0
dl_task_timer+0x1b0/0x228
__hrtimer_run_queues+0x188/0x378
hrtimer_interrupt+0xfc/0x260
...
The problem is that when a SCHED_DEADLINE task (lock holder) is
changed to a lower priority class via sched_setscheduler(), it may
fail to properly inherit the parameters of potential DEADLINE donors
if it didn't already inherit them in the past (shorter deadline than
donor's at that time). This might lead to bandwidth accounting
corruption, as enqueue_task_dl() won't recognize the lock holder as
boosted.
The scenario occurs when:
1. A DEADLINE task (donor) blocks on a PI mutex held by another
DEADLINE task (holder), but the holder doesn't inherit parameters
(e.g., it already has a shorter deadline)
2. sched_setscheduler() changes the holder from DEADLINE to a lower
class while still holding the mutex
3. The holder should now inherit DEADLINE parameters from the donor
and be enqueued with ENQUEUE_REPLENISH, but this doesn't happen
Fix the issue by introducing __setscheduler_dl_pi(), which detects when
a DEADLINE (proper or boosted) task gets setscheduled to a lower
priority class. In case, the function makes the task inherit DEADLINE
parameters of the donoer (pi_se) and sets ENQUEUE_REPLENISH flag to
ensure proper bandwidth accounting during the next enqueue operation.
Fixes: 2279f540ea ("sched/deadline: Fix priority inheritance with multiple scheduling classes")
Reported-by: Bruno Goncalves <bgoncalv@redhat.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260302-upstream-fix-deadline-piboost-b4-v3-1-6ba32184a9e0@redhat.com
- Fix circular locking dependency in cpuset partition code by deferring
housekeeping_update() calls to a workqueue instead of calling them
directly under cpus_read_lock.
- Fix null-ptr-deref in rebuild_sched_domains_cpuslocked() when
generate_sched_domains() returns NULL due to kmalloc failure.
- Fix incorrect cpuset behavior for effective_xcpus in
partition_xcpus_del() and cpuset_update_tasks_cpumask() in
update_cpumasks_hier().
- Fix race between task migration and cgroup iteration.
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Merge tag 'cgroup-for-7.0-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
Pull cgroup fixes from Tejun Heo:
- Fix circular locking dependency in cpuset partition code by
deferring housekeeping_update() calls to a workqueue instead
of calling them directly under cpus_read_lock
- Fix null-ptr-deref in rebuild_sched_domains_cpuslocked() when
generate_sched_domains() returns NULL due to kmalloc failure
- Fix incorrect cpuset behavior for effective_xcpus in
partition_xcpus_del() and cpuset_update_tasks_cpumask()
in update_cpumasks_hier()
- Fix race between task migration and cgroup iteration
* tag 'cgroup-for-7.0-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
cgroup/cpuset: fix null-ptr-deref in rebuild_sched_domains_cpuslocked
cgroup/cpuset: Call housekeeping_update() without holding cpus_read_lock
cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue
cgroup/cpuset: Move housekeeping_update()/rebuild_sched_domains() together
kselftest/cgroup: Simplify test_cpuset_prs.sh by removing "S+" command
cgroup/cpuset: Set isolated_cpus_updating only if isolated_cpus is changed
cgroup/cpuset: Clarify exclusion rules for cpuset internal variables
cgroup/cpuset: Fix incorrect use of cpuset_update_tasks_cpumask() in update_cpumasks_hier()
cgroup/cpuset: Fix incorrect change to effective_xcpus in partition_xcpus_del()
cgroup: fix race between task migration and iteration
- Fix starvation of scx_enable() under fair-class saturation by
offloading the enable path to an RT kthread.
- Fix out-of-bounds access in idle mask initialization on systems with
non-contiguous NUMA node IDs.
- Fix a preemption window during scheduler exit and a refcount underflow
in cgroup init error path.
- Fix SCX_EFLAG_INITIALIZED being a no-op flag.
- Add READ_ONCE() annotations for KCSAN-clean lockless accesses and
replace naked scx_root dereferences with container_of() in kobject
callbacks.
- Tooling and selftest fixes: compilation issues with clang 17,
strtoul() misuse, unused options cleanup, and Kconfig sync.
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Merge tag 'sched_ext-for-7.0-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext
Pull sched_ext fixes from Tejun Heo:
- Fix starvation of scx_enable() under fair-class saturation by
offloading the enable path to an RT kthread
- Fix out-of-bounds access in idle mask initialization on systems with
non-contiguous NUMA node IDs
- Fix a preemption window during scheduler exit and a refcount
underflow in cgroup init error path
- Fix SCX_EFLAG_INITIALIZED being a no-op flag
- Add READ_ONCE() annotations for KCSAN-clean lockless accesses and
replace naked scx_root dereferences with container_of() in kobject
callbacks
- Tooling and selftest fixes: compilation issues with clang 17,
strtoul() misuse, unused options cleanup, and Kconfig sync
* tag 'sched_ext-for-7.0-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
sched_ext: Fix starvation of scx_enable() under fair-class saturation
sched_ext: Remove redundant css_put() in scx_cgroup_init()
selftests/sched_ext: Fix peek_dsq.bpf.c compile error for clang 17
selftests/sched_ext: Add -fms-extensions to bpf build flags
tools/sched_ext: Add -fms-extensions to bpf build flags
sched_ext: Use READ_ONCE() for plain reads of scx_watchdog_timeout
sched_ext: Replace naked scx_root dereferences in kobject callbacks
sched_ext: Use READ_ONCE() for the read side of dsq->nr update
tools/sched_ext: fix strtoul() misuse in scx_hotplug_seq()
sched_ext: Fix SCX_EFLAG_INITIALIZED being a no-op flag
sched_ext: Fix out-of-bounds access in scx_idle_init_masks()
sched_ext: Disable preemption between scx_claim_exit() and kicking helper work
tools/sched_ext: Add Kconfig to sync with upstream
tools/sched_ext: Sync README.md Kconfig with upstream scx
selftests/sched_ext: Remove duplicated unistd.h include in rt_stall.c
tools/sched_ext: scx_sdt: Remove unused '-f' option
tools/sched_ext: scx_central: Remove unused '-p' option
selftests/sched_ext: Fix unused-result warning for read()
selftests/sched_ext: Abort test loop on signal
During scx_enable(), the READY -> ENABLED task switching loop changes the
calling thread's sched_class from fair to ext. Since fair has higher
priority than ext, saturating fair-class workloads can indefinitely starve
the enable thread, hanging the system. This was introduced when the enable
path switched from preempt_disable() to scx_bypass() which doesn't protect
against fair-class starvation. Note that the original preempt_disable()
protection wasn't complete either - in partial switch modes, the calling
thread could still be starved after preempt_enable() as it may have been
switched to ext class.
Fix it by offloading the enable body to a dedicated system-wide RT
(SCHED_FIFO) kthread which cannot be starved by either fair or ext class
tasks. scx_enable() lazily creates the kthread on first use and passes the
ops pointer through a struct scx_enable_cmd containing the kthread_work,
then synchronously waits for completion.
The workfn runs on a different kthread from sch->helper (which runs
disable_work), so it can safely flush disable_work on the error path
without deadlock.
Fixes: 8c2090c504 ("sched_ext: Initialize in bypass mode")
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Tejun Heo <tj@kernel.org>
The iterator css_for_each_descendant_pre() walks the cgroup hierarchy
under cgroup_lock(). It does not increment the reference counts on
yielded css structs.
According to the cgroup documentation, css_put() should only be used
to release a reference obtained via css_get() or css_tryget_online().
Since the iterator does not use either of these to acquire a reference,
calling css_put() in the error path of scx_cgroup_init() causes a
refcount underflow.
Remove the unbalanced css_put() to prevent a potential Use-After-Free
(UAF) vulnerability.
Fixes: 8195136669 ("sched_ext: Add cgroup support")
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_watchdog_timeout is written with WRITE_ONCE() in scx_enable():
WRITE_ONCE(scx_watchdog_timeout, timeout);
However, three read-side accesses use plain reads without the matching
READ_ONCE():
/* check_rq_for_timeouts() - L2824 */
last_runnable + scx_watchdog_timeout
/* scx_watchdog_workfn() - L2852 */
scx_watchdog_timeout / 2
/* scx_enable() - L5179 */
scx_watchdog_timeout / 2
The KCSAN documentation requires that if one accessor uses WRITE_ONCE()
to annotate lock-free access, all other accesses must also use the
appropriate accessor. Plain reads alongside WRITE_ONCE() leave the pair
incomplete and can trigger KCSAN warnings.
Note that scx_tick() already uses the correct READ_ONCE() annotation:
last_check + READ_ONCE(scx_watchdog_timeout)
Fix the three remaining plain reads to match, making all accesses to
scx_watchdog_timeout consistently annotated and KCSAN-clean.
Signed-off-by: zhidao su <suzhidao@xiaomi.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_attr_ops_show() and scx_uevent() access scx_root->ops.name directly.
This is problematic for two reasons:
1. The file-level comment explicitly identifies naked scx_root
dereferences as a temporary measure that needs to be replaced
with proper per-instance access.
2. scx_attr_events_show(), the neighboring sysfs show function in
the same group, already uses the correct pattern:
struct scx_sched *sch = container_of(kobj, struct scx_sched, kobj);
Having inconsistent access patterns in the same sysfs/uevent
group is error-prone.
The kobject embedded in struct scx_sched is initialized as:
kobject_init_and_add(&sch->kobj, &scx_ktype, NULL, "root");
so container_of(kobj, struct scx_sched, kobj) correctly retrieves
the owning scx_sched instance in both callbacks.
Replace the naked scx_root dereferences with container_of()-based
access, consistent with scx_attr_events_show() and in preparation
for proper multi-instance scx_sched support.
Signed-off-by: zhidao su <suzhidao@xiaomi.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_bpf_dsq_nr_queued() reads dsq->nr via READ_ONCE() without holding
any lock, making dsq->nr a lock-free concurrently accessed variable.
However, dsq_mod_nr(), the sole writer of dsq->nr, only uses
WRITE_ONCE() on the write side without the matching READ_ONCE() on the
read side:
WRITE_ONCE(dsq->nr, dsq->nr + delta);
^^^^^^^
plain read -- KCSAN data race
The KCSAN documentation requires that if one accessor uses READ_ONCE()
or WRITE_ONCE() on a variable to annotate lock-free access, all other
accesses must also use the appropriate accessor. A plain read on the
right-hand side of WRITE_ONCE() leaves the pair incomplete and will
trigger KCSAN warnings.
Fix by using READ_ONCE() for the read side of the update:
WRITE_ONCE(dsq->nr, READ_ONCE(dsq->nr) + delta);
This is consistent with scx_bpf_dsq_nr_queued() and makes the
concurrent access annotation complete and KCSAN-clean.
Signed-off-by: zhidao su <suzhidao@xiaomi.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
The deferred rearm of the clock event device after an interrupt and and
other hrtimer optimizations allow now to enable HRTICK for generic entry
architectures.
This decouples preemption from CONFIG_HZ, leaving only the periodic
load-balancer and various accounting things relying on the tick.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163431.937531564@kernel.org
The hrtimer interrupt expires timers and at the end of the interrupt it
rearms the clockevent device for the next expiring timer.
That's obviously correct, but in the case that a expired timer sets
NEED_RESCHED the return from interrupt ends up in schedule(). If HRTICK is
enabled then schedule() will modify the hrtick timer, which causes another
reprogramming of the hardware.
That can be avoided by deferring the rearming to the return from interrupt
path and if the return results in a immediate schedule() invocation then it
can be deferred until the end of schedule(), which avoids multiple rearms
and re-evaluation of the timer wheel.
Add the rearm checks to the existing sched_hrtick_enter/exit() functions,
which already handle the batched rearm of the hrtick timer.
For now this is just placing empty stubs at the right places which are all
optimized out by the compiler until the guard condition becomes true.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163431.208580085@kernel.org
The hrtick timer is frequently rearmed before expiry and most of the time
the new expiry is past the armed one. As this happens on every context
switch it becomes expensive with scheduling heavy work loads especially in
virtual machines as the "hardware" reprogamming implies a VM exit.
hrtimer now provide a lazy rearm mode flag which skips the reprogamming if:
1) The timer was the first expiring timer before the rearm
2) The new expiry time is farther out than the armed time
This avoids a massive amount of reprogramming operations of the hrtick
timer for the price of eventually taking the alredy armed interrupt for
nothing.
Mark the hrtick timer accordingly.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163429.475409346@kernel.org
Tiny adjustments to the hrtick expiry time below 5 microseconds are just
causing extra work for no real value. Filter them out when restarting the
hrtick.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163429.340593047@kernel.org
schedule() provides several mechanisms to update the hrtick timer:
1) When the next task is picked
2) When the balance callbacks are invoked before rq::lock is released
Each of them can result in a first expiring timer and cause a reprogram of
the clock event device.
Solve this by deferring the rearm to the end of schedule() right before
releasing rq::lock by setting a flag on entry which tells hrtick_start() to
cache the runtime constraint in rq::hrtick_delay without touching the timer
itself.
Right before releasing rq::lock evaluate the flags and either rearm or
cancel the hrtick timer.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163429.273068659@kernel.org
Use the static branch based variant and thereby avoid following three
pointers.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163429.203610956@kernel.org
The clock of the hrtick and deadline timers is known to be CLOCK_MONOTONIC.
No point in looking it up via hrtimer_cb_get_time().
Just use ktime_get() directly.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163429.001511662@kernel.org
Since the tick causes hard preemption, the hrtick should too.
Letting the hrtick do lazy preemption completely defeats the purpose, since
it will then still be delayed until a old tick and be dependent on
CONFIG_HZ.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163428.933894105@kernel.org
hrtick_update() was needed when the slice depended on nr_running, all that
code is gone. All that remains is starting the hrtick when nr_running
becomes more than 1.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163428.866374835@kernel.org
The nominal duration for an EEVDF task to run is until its deadline. At
which point the deadline is moved ahead and a new task selection is done.
Try and predict the time 'lost' to higher scheduling classes. Since this is
an estimate, the timer can be both early or late. In case it is early
task_tick_fair() will take the !need_resched() path and restarts the timer.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://patch.msgid.link/20260224163428.798198874@kernel.org
SCX_EFLAG_INITIALIZED is the sole member of enum scx_exit_flags with no
explicit value, so the compiler assigns it 0. This makes the bitwise OR
in scx_ops_init() a no-op:
sch->exit_info->flags |= SCX_EFLAG_INITIALIZED; /* |= 0 */
As a result, BPF schedulers cannot distinguish whether ops.init()
completed successfully by inspecting exit_info->flags.
Assign the value 1LLU << 0 so the flag is actually set.
Fixes: f3aec2adce ("sched_ext: Add SCX_EFLAG_INITIALIZED to indicate successful ops.init()")
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_idle_node_masks is allocated with num_possible_nodes() elements but
indexed by NUMA node IDs via for_each_node(). On systems with
non-contiguous NUMA node numbering (e.g. nodes 0 and 4), node IDs can
exceed the array size, causing out-of-bounds memory corruption.
Use nr_node_ids instead, which represents the maximum node ID range and
is the correct size for arrays indexed by node ID.
Fixes: 7c60329e3521 ("sched_ext: Add NUMA-awareness to the default idle selection policy")
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
The SCHED_DEADLINE scheduler allows reading the statically configured
run-time, deadline, and period parameters through the sched_getattr()
system call. However, there is no immediate way to access, from user space,
the current parameters used within the scheduler: the instantaneous runtime
left in the current cycle, as well as the current absolute deadline.
The `flags' sched_getattr() parameter, so far mandated to contain zero,
now supports the SCHED_GETATTR_FLAG_DL_DYNAMIC=1 flag, to request
retrieval of the leftover runtime and absolute deadline, converted to a
CLOCK_MONOTONIC reference, instead of the statically configured parameters.
This feature is useful for adaptive SCHED_DEADLINE tasks that need to
modify their behavior depending on whether or not there is enough runtime
left in the current period, and/or what is the current absolute deadline.
Notes:
- before returning the instantaneous parameters, the runtime is updated;
- the abs deadline is returned shifted from rq_clock() to ktime_get_ns(),
in CLOCK_MONOTONIC reference; this causes multiple invocations from the
same period to return values that may differ for a few ns (showing some
small drift), albeit the deadline doesn't move, in rq_clock() reference;
- the abs deadline value returned to user-space, as unsigned 64-bit value,
can represent nearly 585 years since boot time;
- setting flags=0 provides the old behavior (retrieve static parameters).
See also the notes from discussion held at OSPM 2025 on the topic
"Making user space aware of current deadline-scheduler parameters".
Signed-off-by: Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Matteo Martelli <matteo.martelli@codethink.co.uk>
Link: https://patch.msgid.link/20250912053937.31636-2-tommaso.cucinotta@santannapisa.it
scx_claim_exit() atomically sets exit_kind, which prevents scx_error() from
triggering further error handling. After claiming exit, the caller must kick
the helper kthread work which initiates bypass mode and teardown.
If the calling task gets preempted between claiming exit and kicking the
helper work, and the BPF scheduler fails to schedule it back (since error
handling is now disabled), the helper work is never queued, bypass mode
never activates, tasks stop being dispatched, and the system wedges.
Disable preemption across scx_claim_exit() and the subsequent work kicking
in all callers - scx_disable() and scx_vexit(). Add
lockdep_assert_preemption_disabled() to scx_claim_exit() to enforce the
requirement.
Fixes: f0e1a0643a ("sched_ext: Implement BPF extensible scheduler class")
Cc: stable@vger.kernel.org # v6.12+
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
The current cpuset partition code is able to dynamically update
the sched domains of a running system and the corresponding
HK_TYPE_DOMAIN housekeeping cpumask to perform what is essentially the
"isolcpus=domain,..." boot command line feature at run time.
The housekeeping cpumask update requires flushing a number of different
workqueues which may not be safe with cpus_read_lock() held as the
workqueue flushing code may acquire cpus_read_lock() or acquiring locks
which have locking dependency with cpus_read_lock() down the chain. Below
is an example of such circular locking problem.
======================================================
WARNING: possible circular locking dependency detected
6.18.0-test+ #2 Tainted: G S
------------------------------------------------------
test_cpuset_prs/10971 is trying to acquire lock:
ffff888112ba4958 ((wq_completion)sync_wq){+.+.}-{0:0}, at: touch_wq_lockdep_map+0x7a/0x180
but task is already holding lock:
ffffffffae47f450 (cpuset_mutex){+.+.}-{4:4}, at: cpuset_partition_write+0x85/0x130
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #4 (cpuset_mutex){+.+.}-{4:4}:
-> #3 (cpu_hotplug_lock){++++}-{0:0}:
-> #2 (rtnl_mutex){+.+.}-{4:4}:
-> #1 ((work_completion)(&arg.work)){+.+.}-{0:0}:
-> #0 ((wq_completion)sync_wq){+.+.}-{0:0}:
Chain exists of:
(wq_completion)sync_wq --> cpu_hotplug_lock --> cpuset_mutex
5 locks held by test_cpuset_prs/10971:
#0: ffff88816810e440 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0xf9/0x1d0
#1: ffff8891ab620890 (&of->mutex#2){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x260/0x5f0
#2: ffff8890a78b83e8 (kn->active#187){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x2b6/0x5f0
#3: ffffffffadf32900 (cpu_hotplug_lock){++++}-{0:0}, at: cpuset_partition_write+0x77/0x130
#4: ffffffffae47f450 (cpuset_mutex){+.+.}-{4:4}, at: cpuset_partition_write+0x85/0x130
Call Trace:
<TASK>
:
touch_wq_lockdep_map+0x93/0x180
__flush_workqueue+0x111/0x10b0
housekeeping_update+0x12d/0x2d0
update_parent_effective_cpumask+0x595/0x2440
update_prstate+0x89d/0xce0
cpuset_partition_write+0xc5/0x130
cgroup_file_write+0x1a5/0x680
kernfs_fop_write_iter+0x3df/0x5f0
vfs_write+0x525/0xfd0
ksys_write+0xf9/0x1d0
do_syscall_64+0x95/0x520
entry_SYSCALL_64_after_hwframe+0x76/0x7e
To avoid such a circular locking dependency problem, we have to
call housekeeping_update() without holding the cpus_read_lock() and
cpuset_mutex. The current set of wq's flushed by housekeeping_update()
may not have work functions that call cpus_read_lock() directly,
but we are likely to extend the list of wq's that are flushed in the
future. Moreover, the current set of work functions may hold locks that
may have cpu_hotplug_lock down the dependency chain.
So housekeeping_update() is now called after releasing cpus_read_lock
and cpuset_mutex at the end of a cpuset operation. These two locks are
then re-acquired later before calling rebuild_sched_domains_locked().
To enable mutual exclusion between the housekeeping_update() call and
other cpuset control file write actions, a new top level cpuset_top_mutex
is introduced. This new mutex will be acquired first to allow sharing
variables used by both code paths. However, cpuset update from CPU
hotplug can still happen in parallel with the housekeeping_update()
call, though that should be rare in production environment.
As cpus_read_lock() is now no longer held when
tmigr_isolated_exclude_cpumask() is called, it needs to acquire it
directly.
The lockdep_is_cpuset_held() is also updated to return true if either
cpuset_top_mutex or cpuset_mutex is held.
Fixes: 03ff735101 ("cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Currently, ops.dequeue() is only invoked when the sched_ext core knows
that a task resides in BPF-managed data structures, which causes it to
miss scheduling property change events. In addition, ops.dequeue()
callbacks are completely skipped when tasks are dispatched to non-local
DSQs from ops.select_cpu(). As a result, BPF schedulers cannot reliably
track task state.
Fix this by guaranteeing that each task entering the BPF scheduler's
custody triggers exactly one ops.dequeue() call when it leaves that
custody, whether the exit is due to a dispatch (regular or via a core
scheduling pick) or to a scheduling property change (e.g.
sched_setaffinity(), sched_setscheduler(), set_user_nice(), NUMA
balancing, etc.).
BPF scheduler custody concept: a task is considered to be in the BPF
scheduler's custody when the scheduler is responsible for managing its
lifecycle. This includes tasks dispatched to user-created DSQs or stored
in the BPF scheduler's internal data structures from ops.enqueue().
Custody ends when the task is dispatched to a terminal DSQ (such as the
local DSQ or %SCX_DSQ_GLOBAL), selected by core scheduling, or removed
due to a property change.
Tasks directly dispatched to terminal DSQs bypass the BPF scheduler
entirely and are never in its custody. Terminal DSQs include:
- Local DSQs (%SCX_DSQ_LOCAL or %SCX_DSQ_LOCAL_ON): per-CPU queues
where tasks go directly to execution.
- Global DSQ (%SCX_DSQ_GLOBAL): the built-in fallback queue where the
BPF scheduler is considered "done" with the task.
As a result, ops.dequeue() is not invoked for tasks directly dispatched
to terminal DSQs.
To identify dequeues triggered by scheduling property changes, introduce
the new ops.dequeue() flag %SCX_DEQ_SCHED_CHANGE: when this flag is set,
the dequeue was caused by a scheduling property change.
New ops.dequeue() semantics:
- ops.dequeue() is invoked exactly once when the task leaves the BPF
scheduler's custody, in one of the following cases:
a) regular dispatch: a task dispatched to a user DSQ or stored in
internal BPF data structures is moved to a terminal DSQ
(ops.dequeue() called without any special flags set),
b) core scheduling dispatch: core-sched picks task before dispatch
(ops.dequeue() called with %SCX_DEQ_CORE_SCHED_EXEC flag set),
c) property change: task properties modified before dispatch,
(ops.dequeue() called with %SCX_DEQ_SCHED_CHANGE flag set).
This allows BPF schedulers to:
- reliably track task ownership and lifecycle,
- maintain accurate accounting of managed tasks,
- update internal state when tasks change properties.
Cc: Tejun Heo <tj@kernel.org>
Cc: Emil Tsalapatis <emil@etsalapatis.com>
Cc: Kuba Piecuch <jpiecuch@google.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This prepares for a later commit fixing the ops.dequeue() semantics.
No functional change intended.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reposition the setting and clearing of sticky_cpu to better define the
scope of SCX-internal migrations.
This ensures @sticky_cpu is set for the entire duration of an internal
migration (from dequeue through enqueue), making it a reliable indicator
that an SCX-internal migration is in progress. The dequeue and enqueue
paths can then use @sticky_cpu to identify internal migrations and skip
BPF scheduler notifications accordingly.
This prepares for a later commit fixing the ops.dequeue() semantics.
No functional change intended.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
CPUs whose rq only have SCHED_IDLE tasks running are considered to be
equivalent to truly idle CPUs during wakeup path. For fork and exec
SCHED_IDLE is even preferred.
This is based on the assumption that the SCHED_IDLE CPU is not in an
idle state and might be in a higher P-state, allowing the task/wakee
to run immediately without sharing the rq.
However this assumption doesn't hold if the wakee has SCHED_IDLE policy
itself, as it will share the rq with existing SCHED_IDLE tasks. In this
case, we are better off continuing to look for a truly idle CPU.
On a Intel Xeon 2-socket with 64 logical cores in total this yields
for kernel compilation using SCHED_IDLE:
+---------+----------------------+----------------------+--------+
| workers | mainline (seconds) | patch (seconds) | delta% |
+=========+======================+======================+========+
| 1 | 4384.728 ± 21.085 | 3843.250 ± 16.235 | -12.35 |
| 2 | 2242.513 ± 2.099 | 1971.696 ± 2.842 | -12.08 |
| 4 | 1199.324 ± 1.823 | 1033.744 ± 1.803 | -13.81 |
| 8 | 649.083 ± 1.959 | 559.123 ± 4.301 | -13.86 |
| 16 | 370.425 ± 0.915 | 325.906 ± 4.623 | -12.02 |
| 32 | 234.651 ± 2.255 | 217.266 ± 0.253 | -7.41 |
| 64 | 202.286 ± 1.452 | 197.977 ± 2.275 | -2.13 |
| 128 | 217.092 ± 1.687 | 212.164 ± 1.138 | -2.27 |
+---------+----------------------+----------------------+--------+
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://patch.msgid.link/20260203184939.2138022-1-christian.loehle@arm.com
Currently if a user enqueues a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.
This lack of consistency cannot be addressed without refactoring the API.
For more details see the Link tag below.
This continues the effort to refactor workqueue APIs, which began with
the introduction of new workqueues and a new alloc_workqueue flag in:
commit 128ea9f6cc ("workqueue: Add system_percpu_wq and system_dfl_wq")
commit 930c2ea566 ("workqueue: Add new WQ_PERCPU flag")
Switch to using system_dfl_wq because system_unbound_wq is going away as part of
a workqueue restructuring.
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/
Link: https://patch.msgid.link/20251107092452.43399-1-marco.crivellari@suse.com
For RT and DL thread, only 'set_next_task_(rt/dl)' will call
'update_stats_wait_end_(rt/dl)' to update schedstats information.
However, during the migration process,
'update_stats_wait_start_(rt/dl)' will be called twice, which
will cause the values of wait_max and wait_sum to be incorrect.
The specific output as follows:
$ cat /proc/6046/task/6046/sched | grep wait
wait_start : 0.000000
wait_max : 496717.080029
wait_sum : 7921540.776553
A complete schedstats information update flow of migrate should be
__update_stats_wait_start() [enter queue A, stage 1] ->
__update_stats_wait_end() [leave queue A, stage 2] ->
__update_stats_wait_start() [enter queue B, stage 3] ->
__update_stats_wait_end() [start running on queue B, stage 4]
Stage 1: prev_wait_start is 0, and in the end, wait_start records the
time of entering the queue.
Stage 2: task_on_rq_migrating(p) is true, and wait_start is updated to
the waiting time on queue A.
Stage 3: prev_wait_start is the waiting time on queue A, wait_start is
the time of entering queue B, and wait_start is expected to be greater
than prev_wait_start. Under this condition, wait_start is updated to
(the moment of entering queue B) - (the waiting time on queue A).
Stage 4: the final wait time = (time when starting to run on queue B)
- (time of entering queue B) + (waiting time on queue A) = waiting
time on queue B + waiting time on queue A.
The current problem is that stage 2 does not call __update_stats_wait_end
to update wait_start, which causes the final computed wait time = waiting
time on queue B + the moment of entering queue A, leading to incorrect
wait_max and wait_sum.
Add 'update_stats_wait_end_(rt/dl)' in 'update_stats_dequeue_(rt/dl)' to
update schedstats information when dequeue_task.
Signed-off-by: Dengjun Su <dengjun.su@mediatek.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260204115959.3183567-1-dengjun.su@mediatek.com
With EAS, a group should be set overloaded if at least 1 CPU in the group
is overutilized but it can happen that a CPU is fully utilized by tasks
because of clamping the compute capacity of the CPU. In such case, the CPU
is not overutilized and as a result should not be set overloaded as well.
group_overloaded being a higher priority than group_misfit, such group can
be selected as the busiest group instead of a group with a mistfit task
and prevents load_balance to select the CPU with the misfit task to pull
the latter on a fitting CPU.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Pierre Gondois <pierre.gondois@arm.com>
Link: https://patch.msgid.link/20260206095454.1520619-1-vincent.guittot@linaro.org
Checking uclamp_min is useless and counterproductive for overutilized state
as misfit can now happen without being in overutilized state.
Since commit e5ed0550c0 ("sched/fair: unlink misfit task from cpu overutilized")
util_fits_cpu returns -1 when uclamp_min is above capacity which is not
considered as cpu overutilized.
Remove the useless rq_util_min parameter.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Qais Yousef <qyousef@layalina.io>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260213101751.3121899-1-vincent.guittot@linaro.org
Since we now use the full weight for avg_vruntime(), also make
__calc_delta() use the full value.
Since weight is effectively NICE_0_LOAD, this is 20 bits on 64bit.
This leaves 44 bits for delta_exec, which is ~16k seconds, way longer
than any one tick would ever be, so no worry about overflow.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Shubhang Kaushik <shubhang@os.amperecomputing.com>
Link: https://patch.msgid.link/20260219080625.183283814%40infradead.org
Zicheng Qu reported that, because avg_vruntime() always includes
cfs_rq->curr, when ->on_rq, place_entity() doesn't work right.
Specifically, the lag scaling in place_entity() relies on
avg_vruntime() being the state *before* placement of the new entity.
However in this case avg_vruntime() will actually already include the
entity, which breaks things.
Also, Zicheng Qu argues that avg_vruntime should be invariant under
reweight. IOW commit 6d71a9c616 ("sched/fair: Fix EEVDF entity
placement bug causing scheduling lag") was wrong!
The issue reported in 6d71a9c616 could possibly be explained by
rounding artifacts -- notably the extreme weight '2' is outside of the
range of avg_vruntime/sum_w_vruntime, since that uses
scale_load_down(). By scaling vruntime by the real weight, but
accounting it in vruntime with a factor 1024 more, the average moves
significantly. However, that is now cured.
Tested by reverting 66951e4860 ("sched/fair: Fix update_cfs_group()
vs DELAY_DEQUEUE") and tracing vruntime and vlag figures again.
Reported-by: Zicheng Qu <quzicheng@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Shubhang Kaushik <shubhang@os.amperecomputing.com>
Link: https://patch.msgid.link/20260219080625.066102672%40infradead.org
Due to the zero_vruntime patch, the deltas are now a lot smaller and
measurement with kernel-build and hackbench runs show about 45 bits
used.
This ensures avg_vruntime() tracks the full weight range, reducing
numerical artifacts in reweight and the like.
Also, lets keep the paranoid debug code around fow now.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Shubhang Kaushik <shubhang@os.amperecomputing.com>
Link: https://patch.msgid.link/20260219080624.942813440%40infradead.org
It turns out that a few workloads (easyWave, fio) have a fairly low
success rate on newidle balance, but still benefit greatly from having
it anyway.
Luckliky these workloads have a faily low newidle rate, so the cost if
doing the newidle is relatively low, even if unsuccessfull.
Add a simple rate based part to the newidle ratio compute, such that
low rate newidle will still have a high newidle ratio.
This cures the easyWave and fio workloads while not affecting the
schbench numbers either (which have a very high newidle rate).
Reported-by: Mario Roy <marioeroy@gmail.com>
Reported-by: "Mohamed Abuelfotoh, Hazem" <abuehaze@amazon.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Mario Roy <marioeroy@gmail.com>
Tested-by: "Mohamed Abuelfotoh, Hazem" <abuehaze@amazon.com>
Link: https://patch.msgid.link/20260127151748.GA1079264@noisy.programming.kicks-ass.net
Kernel test robot reported that
tools/testing/selftests/kvm/hardware_disable_test was failing due to
commit 704069649b ("sched/core: Rework sched_class::wakeup_preempt()
and rq_modified_*()")
It turns out there were two related problems that could lead to a
missed preemption:
- when hitting newidle balance from the idle thread, it would elevate
rb->next_class from &idle_sched_class to &fair_sched_class, causing
later wakeup_preempt() calls to not hit the sched_class_above()
case, and not issue resched_curr().
Notably, this modification pattern should only lower the
next_class, and never raise it. Create two new helper functions to
wrap this.
- when doing schedule_idle(), it was possible to miss (re)setting
rq->next_class to &idle_sched_class, leading to the very same
problem.
Cc: Sean Christopherson <seanjc@google.com>
Fixes: 704069649b ("sched/core: Rework sched_class::wakeup_preempt() and rq_modified_*()")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202602122157.4e861298-lkp@intel.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260218163329.GQ1395416@noisy.programming.kicks-ass.net
Vincent reported that he was seeing undue lag clamping in a mixed
slice workload. Implement the max_slice tracking as per the todo
comment.
Fixes: 147f3efaa2 ("sched/fair: Implement an EEVDF-like scheduling policy")
Reported-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Shubhang Kaushik <shubhang@os.amperecomputing.com>
Link: https://patch.msgid.link/20250422101628.GA33555@noisy.programming.kicks-ass.net
In the EEVDF framework with Run-to-Parity protection, `se->vprot` is an
independent variable defining the virtual protection timestamp.
When `reweight_entity()` is called (e.g., via nice/renice), it performs
the following actions to preserve Lag consistency:
1. Scales `se->vlag` based on the new weight.
2. Calls `place_entity()`, which recalculates `se->vruntime` based on
the new weight and scaled lag.
However, the current implementation fails to update `se->vprot`, leading
to mismatches between the task's actual runtime and its expected duration.
Fixes: 63304558ba ("sched/eevdf: Curb wakeup-preemption")
Suggested-by: Zhang Qiao <zhangqiao22@huawei.com>
Signed-off-by: Wang Tao <wangtao554@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Shubhang Kaushik <shubhang@os.amperecomputing.com>
Link: https://patch.msgid.link/20260120123113.3518950-1-wangtao554@huawei.com
We should not (re)set slice protection in the sched_change pattern
which calls put_prev_task() / set_next_task().
Fixes: 63304558ba ("sched/eevdf: Curb wakeup-preemption")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Shubhang Kaushik <shubhang@os.amperecomputing.com>
Link: https://patch.msgid.link/20260219080624.561421378%40infradead.org
It turns out that zero_vruntime tracking is broken when there is but a single
task running. Current update paths are through __{en,de}queue_entity(), and
when there is but a single task, pick_next_task() will always return that one
task, and put_prev_set_next_task() will end up in neither function.
This can cause entity_key() to grow indefinitely large and cause overflows,
leading to much pain and suffering.
Furtermore, doing update_zero_vruntime() from __{de,en}queue_entity(), which
are called from {set_next,put_prev}_entity() has problems because:
- set_next_entity() calls __dequeue_entity() before it does cfs_rq->curr = se.
This means the avg_vruntime() will see the removal but not current, missing
the entity for accounting.
- put_prev_entity() calls __enqueue_entity() before it does cfs_rq->curr =
NULL. This means the avg_vruntime() will see the addition *and* current,
leading to double accounting.
Both cases are incorrect/inconsistent.
Noting that avg_vruntime is already called on each {en,de}queue, remove the
explicit avg_vruntime() calls (which removes an extra 64bit division for each
{en,de}queue) and have avg_vruntime() update zero_vruntime itself.
Additionally, have the tick call avg_vruntime() -- discarding the result, but
for the side-effect of updating zero_vruntime.
While there, optimize avg_vruntime() by noting that the average of one value is
rather trivial to compute.
Test case:
# taskset -c -p 1 $$
# taskset -c 2 bash -c 'while :; do :; done&'
# cat /sys/kernel/debug/sched/debug | awk '/^cpu#/ {P=0} /^cpu#2,/ {P=1} {if (P) print $0}' | grep -e zero_vruntime -e "^>"
PRE:
.zero_vruntime : 31316.407903
>R bash 487 50787.345112 E 50789.145972 2.800000 50780.298364 16 120 0.000000 0.000000 0.000000 /
.zero_vruntime : 382548.253179
>R bash 487 427275.204288 E 427276.003584 2.800000 427268.157540 23 120 0.000000 0.000000 0.000000 /
POST:
.zero_vruntime : 17259.709467
>R bash 526 17259.709467 E 17262.509467 2.800000 16915.031624 9 120 0.000000 0.000000 0.000000 /
.zero_vruntime : 18702.723356
>R bash 526 18702.723356 E 18705.523356 2.800000 18358.045513 9 120 0.000000 0.000000 0.000000 /
Fixes: 79f3f9bedd ("sched/eevdf: Fix min_vruntime vs avg_vruntime")
Reported-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Shubhang Kaushik <shubhang@os.amperecomputing.com>
Link: https://patch.msgid.link/20260219080624.438854780%40infradead.org
This converts some of the visually simpler cases that have been split
over multiple lines. I only did the ones that are easy to verify the
resulting diff by having just that final GFP_KERNEL argument on the next
line.
Somebody should probably do a proper coccinelle script for this, but for
me the trivial script actually resulted in an assertion failure in the
middle of the script. I probably had made it a bit _too_ trivial.
So after fighting that far a while I decided to just do some of the
syntactically simpler cases with variations of the previous 'sed'
scripts.
The more syntactically complex multi-line cases would mostly really want
whitespace cleanup anyway.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This was done entirely with mindless brute force, using
git grep -l '\<k[vmz]*alloc_objs*(.*, GFP_KERNEL)' |
xargs sed -i 's/\(alloc_objs*(.*\), GFP_KERNEL)/\1)/'
to convert the new alloc_obj() users that had a simple GFP_KERNEL
argument to just drop that argument.
Note that due to the extreme simplicity of the scripting, any slightly
more complex cases spread over multiple lines would not be triggered:
they definitely exist, but this covers the vast bulk of the cases, and
the resulting diff is also then easier to check automatically.
For the same reason the 'flex' versions will be done as a separate
conversion.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:
Single allocations: kmalloc(sizeof(TYPE), ...)
are replaced with: kmalloc_obj(TYPE, ...)
Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with: kmalloc_objs(TYPE, COUNT, ...)
Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...)
(where TYPE may also be *VAR)
The resulting allocations no longer return "void *", instead returning
"TYPE *".
Signed-off-by: Kees Cook <kees@kernel.org>
Total patches: 107
Reviews/patch: 1.07
Reviewed rate: 67%
- The 2 patch series "ocfs2: give ocfs2 the ability to reclaim
suballocator free bg" from Heming Zhao saves disk space by teaching
ocfs2 to reclaim suballocator block group space.
- The 4 patch series "Add ARRAY_END(), and use it to fix off-by-one
bugs" from Alejandro Colomar adds the ARRAY_END() macro and uses it in
various places.
- The 2 patch series "vmcoreinfo: support VMCOREINFO_BYTES larger than
PAGE_SIZE" from Pnina Feder makes the vmcore code future-safe, if
VMCOREINFO_BYTES ever exceeds the page size.
- The 7 patch series "kallsyms: Prevent invalid access when showing
module buildid" from Petr Mladek cleans up kallsyms code related to
module buildid and fixes an invalid access crash when printing
backtraces.
- The 3 patch series "Address page fault in
ima_restore_measurement_list()" from Harshit Mogalapalli fixes a
kexec-related crash that can occur when booting the second-stage kernel
on x86.
- The 6 patch series "kho: ABI headers and Documentation updates" from
Mike Rapoport updates the kexec handover ABI documentation.
- The 4 patch series "Align atomic storage" from Finn Thain adds the
__aligned attribute to atomic_t and atomic64_t definitions to get
natural alignment of both types on csky, m68k, microblaze, nios2,
openrisc and sh.
- The 2 patch series "kho: clean up page initialization logic" from
Pratyush Yadav simplifies the page initialization logic in
kho_restore_page().
- The 6 patch series "Unload linux/kernel.h" from Yury Norov moves
several things out of kernel.h and into more appropriate places.
- The 7 patch series "don't abuse task_struct.group_leader" from Oleg
Nesterov removes the usage of ->group_leader when it is "obviously
unnecessary".
- The 5 patch series "list private v2 & luo flb" from Pasha Tatashin
adds some infrastructure improvements to the live update orchestrator.
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Merge tag 'mm-nonmm-stable-2026-02-12-10-48' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Pull non-MM updates from Andrew Morton:
- "ocfs2: give ocfs2 the ability to reclaim suballocator free bg" saves
disk space by teaching ocfs2 to reclaim suballocator block group
space (Heming Zhao)
- "Add ARRAY_END(), and use it to fix off-by-one bugs" adds the
ARRAY_END() macro and uses it in various places (Alejandro Colomar)
- "vmcoreinfo: support VMCOREINFO_BYTES larger than PAGE_SIZE" makes
the vmcore code future-safe, if VMCOREINFO_BYTES ever exceeds the
page size (Pnina Feder)
- "kallsyms: Prevent invalid access when showing module buildid" cleans
up kallsyms code related to module buildid and fixes an invalid
access crash when printing backtraces (Petr Mladek)
- "Address page fault in ima_restore_measurement_list()" fixes a
kexec-related crash that can occur when booting the second-stage
kernel on x86 (Harshit Mogalapalli)
- "kho: ABI headers and Documentation updates" updates the kexec
handover ABI documentation (Mike Rapoport)
- "Align atomic storage" adds the __aligned attribute to atomic_t and
atomic64_t definitions to get natural alignment of both types on
csky, m68k, microblaze, nios2, openrisc and sh (Finn Thain)
- "kho: clean up page initialization logic" simplifies the page
initialization logic in kho_restore_page() (Pratyush Yadav)
- "Unload linux/kernel.h" moves several things out of kernel.h and into
more appropriate places (Yury Norov)
- "don't abuse task_struct.group_leader" removes the usage of
->group_leader when it is "obviously unnecessary" (Oleg Nesterov)
- "list private v2 & luo flb" adds some infrastructure improvements to
the live update orchestrator (Pasha Tatashin)
* tag 'mm-nonmm-stable-2026-02-12-10-48' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (107 commits)
watchdog/hardlockup: simplify perf event probe and remove per-cpu dependency
procfs: fix missing RCU protection when reading real_parent in do_task_stat()
watchdog/softlockup: fix sample ring index wrap in need_counting_irqs()
kcsan, compiler_types: avoid duplicate type issues in BPF Type Format
kho: fix doc for kho_restore_pages()
tests/liveupdate: add in-kernel liveupdate test
liveupdate: luo_flb: introduce File-Lifecycle-Bound global state
liveupdate: luo_file: Use private list
list: add kunit test for private list primitives
list: add primitives for private list manipulations
delayacct: fix uapi timespec64 definition
panic: add panic_force_cpu= parameter to redirect panic to a specific CPU
netclassid: use thread_group_leader(p) in update_classid_task()
RDMA/umem: don't abuse current->group_leader
drm/pan*: don't abuse current->group_leader
drm/amd: kill the outdated "Only the pthreads threading model is supported" checks
drm/amdgpu: don't abuse current->group_leader
android/binder: use same_thread_group(proc->tsk, current) in binder_mmap()
android/binder: don't abuse current->group_leader
kho: skip memoryless NUMA nodes when reserving scratch areas
...
- Move C example schedulers back from the external scx repo to
tools/sched_ext as the authoritative source. scx_userland and scx_pair
are returning while scx_sdt (BPF arena-based task data management) is
new. These schedulers will be dropped from the external repo.
- Improve error reporting by adding scx_bpf_error() calls when DSQ
creation fails across all in-tree schedulers.
- Avoid redundant irq_work_queue() calls in destroy_dsq() by only
queueing when llist_add() indicates an empty list.
- Fix flaky init_enable_count selftest by properly synchronizing
pre-forked children using a pipe instead of sleep().
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Merge tag 'sched_ext-for-6.20' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext
Pull sched_ext updates from Tejun Heo:
- Move C example schedulers back from the external scx repo to
tools/sched_ext as the authoritative source. scx_userland and
scx_pair are returning while scx_sdt (BPF arena-based task data
management) is new. These schedulers will be dropped from the
external repo.
- Improve error reporting by adding scx_bpf_error() calls when DSQ
creation fails across all in-tree schedulers
- Avoid redundant irq_work_queue() calls in destroy_dsq() by only
queueing when llist_add() indicates an empty list
- Fix flaky init_enable_count selftest by properly synchronizing
pre-forked children using a pipe instead of sleep()
* tag 'sched_ext-for-6.20' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
selftests/sched_ext: Fix init_enable_count flakiness
tools/sched_ext: Fix data header access during free in scx_sdt
tools/sched_ext: Add error logging for dsq creation failures in remaining schedulers
tools/sched_ext: add arena based scheduler
tools/sched_ext: add scx_pair scheduler
tools/sched_ext: add scx_userland scheduler
sched_ext: Add error logging for dsq creation failures
sched_ext: Avoid multiple irq_work_queue() calls in destroy_dsq()
Shinichiro reported a KASAN UAF, which is actually an out of bounds access
in the MMCID management code.
CPU0 CPU1
T1 runs in userspace
T0: fork(T4) -> Switch to per CPU CID mode
fixup() set MM_CID_TRANSIT on T1/CPU1
T4 exit()
T3 exit()
T2 exit()
T1 exit() switch to per task mode
---> Out of bounds access.
As T1 has not scheduled after T0 set the TRANSIT bit, it exits with the
TRANSIT bit set. sched_mm_cid_remove_user() clears the TRANSIT bit in
the task and drops the CID, but it does not touch the per CPU storage.
That's functionally correct because a CID is only owned by the CPU when
the ONCPU bit is set, which is mutually exclusive with the TRANSIT flag.
Now sched_mm_cid_exit() assumes that the CID is CPU owned because the
prior mode was per CPU. It invokes mm_drop_cid_on_cpu() which clears the
not set ONCPU bit and then invokes clear_bit() with an insanely large
bit number because TRANSIT is set (bit 29).
Prevent that by actually validating that the CID is CPU owned in
mm_drop_cid_on_cpu().
Fixes: 007d84287c ("sched/mmcid: Drop per CPU CID immediately when switching to per task mode")
Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Cc: stable@vger.kernel.org
Closes: https://lore.kernel.org/aYsZrixn9b6s_2zL@shinmob
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
clock interface, taming the include hell by splitting the pv_ops structure
and removing of a bunch of obsolete code. Work by Juergen Gross.
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Merge tag 'x86_paravirt_for_v7.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 paravirt updates from Borislav Petkov:
- A nice cleanup to the paravirt code containing a unification of the
paravirt clock interface, taming the include hell by splitting the
pv_ops structure and removing of a bunch of obsolete code (Juergen
Gross)
* tag 'x86_paravirt_for_v7.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (23 commits)
x86/paravirt: Use XOR r32,r32 to clear register in pv_vcpu_is_preempted()
x86/paravirt: Remove trailing semicolons from alternative asm templates
x86/pvlocks: Move paravirt spinlock functions into own header
x86/paravirt: Specify pv_ops array in paravirt macros
x86/paravirt: Allow pv-calls outside paravirt.h
objtool: Allow multiple pv_ops arrays
x86/xen: Drop xen_mmu_ops
x86/xen: Drop xen_cpu_ops
x86/xen: Drop xen_irq_ops
x86/paravirt: Move pv_native_*() prototypes to paravirt.c
x86/paravirt: Introduce new paravirt-base.h header
x86/paravirt: Move paravirt_sched_clock() related code into tsc.c
x86/paravirt: Use common code for paravirt_steal_clock()
riscv/paravirt: Use common code for paravirt_steal_clock()
loongarch/paravirt: Use common code for paravirt_steal_clock()
arm64/paravirt: Use common code for paravirt_steal_clock()
arm/paravirt: Use common code for paravirt_steal_clock()
sched: Move clock related paravirt code to kernel/sched
paravirt: Remove asm/paravirt_api_clock.h
x86/paravirt: Move thunk macros to paravirt_types.h
...
Scheduler Kconfig space updates:
- Further consolidate configurable preemption modes: reduce
the number of architectures that are allowed to offer
PREEMPT_NONE and PREEMPT_VOLUNTARY, reducing the number
of preemption models from four to just two: 'full' and 'lazy'
on up-to-date architectures (arm64, loongarch, powerpc,
riscv, s390, x86).
None and voluntary are only available as legacy features
on platforms that don't implement lazy preemption yet,
or which don't even support preemption.
The goal is to eventually remove cond_resched() and
voluntary preemption altogether.
(Peter Zijlstra)
RSEQ based 'scheduler time slice extension' support:
This allows a thread to request a time slice extension when it
enters a critical section to avoid contention on a resource when
the thread is scheduled out inside of the critical section.
- Add fields and constants for time slice extension
- Provide static branch for time slice extensions
- Add statistics for time slice extensions
- Add prctl() to enable time slice extensions
- Implement sys_rseq_slice_yield()
- Implement syscall entry work for time slice extensions
- Implement time slice extension enforcement timer
- Reset slice extension when scheduled
- Implement rseq_grant_slice_extension()
- entry: Hook up rseq time slice extension
- selftests: Implement time slice extension test
(Thomas Gleixner)
- Allow registering RSEQ with slice extension
- Move slice_ext_nsec to debugfs
- Lower default slice extension
- selftests/rseq: Add rseq slice histogram script
(Peter Zijlstra)
Scheduler performance/scalability improvements:
- Update rq->avg_idle when a task is moved to an idle CPU,
which improves the scalability of various workloads.
(Shubhang Kaushik)
- Reorder fields in 'struct rq' for better caching
(Blake Jones)
- Fair scheduler SMP NOHZ balancing code speedups:
- Move checking for nohz cpus after time check
- Change likelyhood of nohz.nr_cpus
- Remove nohz.nr_cpus and use weight of cpumask instead
(Shrikanth Hegde)
- Avoid false sharing for sched_clock_irqtime (Wangyang Guo)
- Drop useless cpumask_empty() in find_energy_efficient_cpu()
- Simplify task_numa_find_cpu()
- Use cpumask_weight_and() in sched_balance_find_dst_group()
(Yury Norov)
DL scheduler updates:
- Add a deadline server for sched_ext tasks (by Andrea Righi and
Joel Fernandes, with fixes by Peter Zijlstra)
RT scheduler updates:
- Skip currently executing CPU in rto_next_cpu() (Chen Jinghuang)
Entry code updates and performance improvements, which is part of the
scheduler tree in this cycle due to interdependencies with the RSEQ
based time slice extension work:
- Remove unused syscall argument from syscall_trace_enter()
- Rework syscall_exit_to_user_mode_work() for architecture reuse
- Add arch_ptrace_report_syscall_entry/exit()
- Inline syscall_exit_work() and syscall_trace_enter()
(Jinjie Ruan)
Scheduler core updates:
- Rework sched_class::wakeup_preempt() and rq_modified_*()
- Avoid rq->lock bouncing in sched_balance_newidle()
- Rename rcu_dereference_check_sched_domain() =>
rcu_dereference_sched_domain()
- <linux/compiler_types.h>: Add the __signed_scalar_typeof() helper
(Peter Zijlstra)
Fair scheduler updates/refactoring:
- Fold the sched_avg update
- Change rcu_dereference_check_sched_domain() to rcu-sched
- Switch to rcu_dereference_all()
- Remove superfluous rcu_read_lock()
- Limit hrtick work
(Peter Zijlstra)
- Join two #ifdef CONFIG_FAIR_GROUP_SCHED blocks
- Clean up comments in 'struct cfs_rq'
- Separate se->vlag from se->vprot
- Rename cfs_rq::avg_load to cfs_rq::sum_weight
- Rename cfs_rq::avg_vruntime to ::sum_w_vruntime & helper functions
- Introduce and use the vruntime_cmp() and vruntime_op() wrappers
for wrapped-signed aritmetics
- Sort out 'blocked_load*' namespace noise
(Ingo Molnar)
Scheduler debugging code updates:
- Export hidden tracepoints to modules (Gabriele Monaco)
- Convert copy_from_user() + kstrtouint() to kstrtouint_from_user()
(Fushuai Wang)
- Add assertions to QUEUE_CLASS (Peter Zijlstra)
- hrtimer: Fix tracing oddity (Thomas Gleixner)
Misc fixes and cleanups:
- Re-evaluate scheduling when migrating queued tasks out of
throttled cgroups (Zicheng Qu)
- Remove task_struct->faults_disabled_mapping (Christoph Hellwig)
- Fix math notation errors in avg_vruntime comment (Zhan Xusheng)
- sched/cpufreq: Use %pe format for PTR_ERR() printing (zenghongling)
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-core-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler updates from Ingo Molnar:
"Scheduler Kconfig space updates:
- Further consolidate configurable preemption modes (Peter Zijlstra)
Reduce the number of architectures that are allowed to offer
PREEMPT_NONE and PREEMPT_VOLUNTARY, reducing the number of
preemption models from four to just two: 'full' and 'lazy' on
up-to-date architectures (arm64, loongarch, powerpc, riscv, s390,
x86).
None and voluntary are only available as legacy features on
platforms that don't implement lazy preemption yet, or which don't
even support preemption.
The goal is to eventually remove cond_resched() and voluntary
preemption altogether.
RSEQ based 'scheduler time slice extension' support (Thomas Gleixner
and Peter Zijlstra):
This allows a thread to request a time slice extension when it enters
a critical section to avoid contention on a resource when the thread
is scheduled out inside of the critical section.
- Add fields and constants for time slice extension
- Provide static branch for time slice extensions
- Add statistics for time slice extensions
- Add prctl() to enable time slice extensions
- Implement sys_rseq_slice_yield()
- Implement syscall entry work for time slice extensions
- Implement time slice extension enforcement timer
- Reset slice extension when scheduled
- Implement rseq_grant_slice_extension()
- entry: Hook up rseq time slice extension
- selftests: Implement time slice extension test
- Allow registering RSEQ with slice extension
- Move slice_ext_nsec to debugfs
- Lower default slice extension
- selftests/rseq: Add rseq slice histogram script
Scheduler performance/scalability improvements:
- Update rq->avg_idle when a task is moved to an idle CPU, which
improves the scalability of various workloads (Shubhang Kaushik)
- Reorder fields in 'struct rq' for better caching (Blake Jones)
- Fair scheduler SMP NOHZ balancing code speedups (Shrikanth Hegde):
- Move checking for nohz cpus after time check
- Change likelyhood of nohz.nr_cpus
- Remove nohz.nr_cpus and use weight of cpumask instead
- Avoid false sharing for sched_clock_irqtime (Wangyang Guo)
- Cleanups (Yury Norov):
- Drop useless cpumask_empty() in find_energy_efficient_cpu()
- Simplify task_numa_find_cpu()
- Use cpumask_weight_and() in sched_balance_find_dst_group()
DL scheduler updates:
- Add a deadline server for sched_ext tasks (by Andrea Righi and Joel
Fernandes, with fixes by Peter Zijlstra)
RT scheduler updates:
- Skip currently executing CPU in rto_next_cpu() (Chen Jinghuang)
Entry code updates and performance improvements (Jinjie Ruan)
This is part of the scheduler tree in this cycle due to inter-
dependencies with the RSEQ based time slice extension work:
- Remove unused syscall argument from syscall_trace_enter()
- Rework syscall_exit_to_user_mode_work() for architecture reuse
- Add arch_ptrace_report_syscall_entry/exit()
- Inline syscall_exit_work() and syscall_trace_enter()
Scheduler core updates (Peter Zijlstra):
- Rework sched_class::wakeup_preempt() and rq_modified_*()
- Avoid rq->lock bouncing in sched_balance_newidle()
- Rename rcu_dereference_check_sched_domain() =>
rcu_dereference_sched_domain()
- <linux/compiler_types.h>: Add the __signed_scalar_typeof() helper
Fair scheduler updates/refactoring (Peter Zijlstra and Ingo Molnar):
- Fold the sched_avg update
- Change rcu_dereference_check_sched_domain() to rcu-sched
- Switch to rcu_dereference_all()
- Remove superfluous rcu_read_lock()
- Limit hrtick work
- Join two #ifdef CONFIG_FAIR_GROUP_SCHED blocks
- Clean up comments in 'struct cfs_rq'
- Separate se->vlag from se->vprot
- Rename cfs_rq::avg_load to cfs_rq::sum_weight
- Rename cfs_rq::avg_vruntime to ::sum_w_vruntime & helper functions
- Introduce and use the vruntime_cmp() and vruntime_op() wrappers for
wrapped-signed aritmetics
- Sort out 'blocked_load*' namespace noise
Scheduler debugging code updates:
- Export hidden tracepoints to modules (Gabriele Monaco)
- Convert copy_from_user() + kstrtouint() to kstrtouint_from_user()
(Fushuai Wang)
- Add assertions to QUEUE_CLASS (Peter Zijlstra)
- hrtimer: Fix tracing oddity (Thomas Gleixner)
Misc fixes and cleanups:
- Re-evaluate scheduling when migrating queued tasks out of throttled
cgroups (Zicheng Qu)
- Remove task_struct->faults_disabled_mapping (Christoph Hellwig)
- Fix math notation errors in avg_vruntime comment (Zhan Xusheng)
- sched/cpufreq: Use %pe format for PTR_ERR() printing
(zenghongling)"
* tag 'sched-core-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (64 commits)
sched: Re-evaluate scheduling when migrating queued tasks out of throttled cgroups
sched/cpufreq: Use %pe format for PTR_ERR() printing
sched/rt: Skip currently executing CPU in rto_next_cpu()
sched/clock: Avoid false sharing for sched_clock_irqtime
selftests/sched_ext: Add test for DL server total_bw consistency
selftests/sched_ext: Add test for sched_ext dl_server
sched/debug: Fix dl_server (re)start conditions
sched/debug: Add support to change sched_ext server params
sched_ext: Add a DL server for sched_ext tasks
sched/debug: Stop and start server based on if it was active
sched/debug: Fix updating of ppos on server write ops
sched/deadline: Clear the defer params
entry: Inline syscall_exit_work() and syscall_trace_enter()
entry: Add arch_ptrace_report_syscall_entry/exit()
entry: Rework syscall_exit_to_user_mode_work() for architecture reuse
entry: Remove unused syscall argument from syscall_trace_enter()
sched: remove task_struct->faults_disabled_mapping
sched: Update rq->avg_idle when a task is moved to an idle CPU
selftests/rseq: Add rseq slice histogram script
hrtimer: Fix trace oddity
...
Lock debugging:
- Implement compiler-driven static analysis locking context
checking, using the upcoming Clang 22 compiler's context
analysis features. (Marco Elver)
We removed Sparse context analysis support, because prior to
removal even a defconfig kernel produced 1,700+ context
tracking Sparse warnings, the overwhelming majority of which
are false positives. On an allmodconfig kernel the number of
false positive context tracking Sparse warnings grows to
over 5,200... On the plus side of the balance actual locking
bugs found by Sparse context analysis is also rather ... sparse:
I found only 3 such commits in the last 3 years. So the
rate of false positives and the maintenance overhead is
rather high and there appears to be no active policy in
place to achieve a zero-warnings baseline to move the
annotations & fixers to developers who introduce new code.
Clang context analysis is more complete and more aggressive
in trying to find bugs, at least in principle. Plus it has
a different model to enabling it: it's enabled subsystem by
subsystem, which results in zero warnings on all relevant
kernel builds (as far as our testing managed to cover it).
Which allowed us to enable it by default, similar to other
compiler warnings, with the expectation that there are no
warnings going forward. This enforces a zero-warnings baseline
on clang-22+ builds. (Which are still limited in distribution,
admittedly.)
Hopefully the Clang approach can lead to a more maintainable
zero-warnings status quo and policy, with more and more
subsystems and drivers enabling the feature. Context tracking
can be enabled for all kernel code via WARN_CONTEXT_ANALYSIS_ALL=y
(default disabled), but this will generate a lot of false positives.
( Having said that, Sparse support could still be added back,
if anyone is interested - the removal patch is still
relatively straightforward to revert at this stage. )
Rust integration updates: (Alice Ryhl, Fujita Tomonori, Boqun Feng)
- Add support for Atomic<i8/i16/bool> and replace most Rust native
AtomicBool usages with Atomic<bool>
- Clean up LockClassKey and improve its documentation
- Add missing Send and Sync trait implementation for SetOnce
- Make ARef Unpin as it is supposed to be
- Add __rust_helper to a few Rust helpers as a preparation for
helper LTO
- Inline various lock related functions to avoid additional
function calls.
WW mutexes:
- Extend ww_mutex tests and other test-ww_mutex updates (John Stultz)
Misc fixes and cleanups:
- rcu: Mark lockdep_assert_rcu_helper() __always_inline
(Arnd Bergmann)
- locking/local_lock: Include more missing headers (Peter Zijlstra)
- seqlock: fix scoped_seqlock_read kernel-doc (Randy Dunlap)
- rust: sync: Replace `kernel::c_str!` with C-Strings
(Tamir Duberstein)
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'locking-core-2026-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
"Lock debugging:
- Implement compiler-driven static analysis locking context checking,
using the upcoming Clang 22 compiler's context analysis features
(Marco Elver)
We removed Sparse context analysis support, because prior to
removal even a defconfig kernel produced 1,700+ context tracking
Sparse warnings, the overwhelming majority of which are false
positives. On an allmodconfig kernel the number of false positive
context tracking Sparse warnings grows to over 5,200... On the plus
side of the balance actual locking bugs found by Sparse context
analysis is also rather ... sparse: I found only 3 such commits in
the last 3 years. So the rate of false positives and the
maintenance overhead is rather high and there appears to be no
active policy in place to achieve a zero-warnings baseline to move
the annotations & fixers to developers who introduce new code.
Clang context analysis is more complete and more aggressive in
trying to find bugs, at least in principle. Plus it has a different
model to enabling it: it's enabled subsystem by subsystem, which
results in zero warnings on all relevant kernel builds (as far as
our testing managed to cover it). Which allowed us to enable it by
default, similar to other compiler warnings, with the expectation
that there are no warnings going forward. This enforces a
zero-warnings baseline on clang-22+ builds (Which are still limited
in distribution, admittedly)
Hopefully the Clang approach can lead to a more maintainable
zero-warnings status quo and policy, with more and more subsystems
and drivers enabling the feature. Context tracking can be enabled
for all kernel code via WARN_CONTEXT_ANALYSIS_ALL=y (default
disabled), but this will generate a lot of false positives.
( Having said that, Sparse support could still be added back,
if anyone is interested - the removal patch is still
relatively straightforward to revert at this stage. )
Rust integration updates: (Alice Ryhl, Fujita Tomonori, Boqun Feng)
- Add support for Atomic<i8/i16/bool> and replace most Rust native
AtomicBool usages with Atomic<bool>
- Clean up LockClassKey and improve its documentation
- Add missing Send and Sync trait implementation for SetOnce
- Make ARef Unpin as it is supposed to be
- Add __rust_helper to a few Rust helpers as a preparation for
helper LTO
- Inline various lock related functions to avoid additional function
calls
WW mutexes:
- Extend ww_mutex tests and other test-ww_mutex updates (John
Stultz)
Misc fixes and cleanups:
- rcu: Mark lockdep_assert_rcu_helper() __always_inline (Arnd
Bergmann)
- locking/local_lock: Include more missing headers (Peter Zijlstra)
- seqlock: fix scoped_seqlock_read kernel-doc (Randy Dunlap)
- rust: sync: Replace `kernel::c_str!` with C-Strings (Tamir
Duberstein)"
* tag 'locking-core-2026-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (90 commits)
locking/rwlock: Fix write_trylock_irqsave() with CONFIG_INLINE_WRITE_TRYLOCK
rcu: Mark lockdep_assert_rcu_helper() __always_inline
compiler-context-analysis: Remove __assume_ctx_lock from initializers
tomoyo: Use scoped init guard
crypto: Use scoped init guard
kcov: Use scoped init guard
compiler-context-analysis: Introduce scoped init guards
cleanup: Make __DEFINE_LOCK_GUARD handle commas in initializers
seqlock: fix scoped_seqlock_read kernel-doc
tools: Update context analysis macros in compiler_types.h
rust: sync: Replace `kernel::c_str!` with C-Strings
rust: sync: Inline various lock related methods
rust: helpers: Move #define __rust_helper out of atomic.c
rust: wait: Add __rust_helper to helpers
rust: time: Add __rust_helper to helpers
rust: task: Add __rust_helper to helpers
rust: sync: Add __rust_helper to helpers
rust: refcount: Add __rust_helper to helpers
rust: rcu: Add __rust_helper to helpers
rust: processor: Add __rust_helper to helpers
...
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Merge tag 'bpf-next-7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next
Pull bpf updates from Alexei Starovoitov:
- Support associating BPF program with struct_ops (Amery Hung)
- Switch BPF local storage to rqspinlock and remove recursion detection
counters which were causing false positives (Amery Hung)
- Fix live registers marking for indirect jumps (Anton Protopopov)
- Introduce execution context detection BPF helpers (Changwoo Min)
- Improve verifier precision for 32bit sign extension pattern
(Cupertino Miranda)
- Optimize BTF type lookup by sorting vmlinux BTF and doing binary
search (Donglin Peng)
- Allow states pruning for misc/invalid slots in iterator loops (Eduard
Zingerman)
- In preparation for ASAN support in BPF arenas teach libbpf to move
global BPF variables to the end of the region and enable arena kfuncs
while holding locks (Emil Tsalapatis)
- Introduce support for implicit arguments in kfuncs and migrate a
number of them to new API. This is a prerequisite for cgroup
sub-schedulers in sched-ext (Ihor Solodrai)
- Fix incorrect copied_seq calculation in sockmap (Jiayuan Chen)
- Fix ORC stack unwind from kprobe_multi (Jiri Olsa)
- Speed up fentry attach by using single ftrace direct ops in BPF
trampolines (Jiri Olsa)
- Require frozen map for calculating map hash (KP Singh)
- Fix lock entry creation in TAS fallback in rqspinlock (Kumar
Kartikeya Dwivedi)
- Allow user space to select cpu in lookup/update operations on per-cpu
array and hash maps (Leon Hwang)
- Make kfuncs return trusted pointers by default (Matt Bobrowski)
- Introduce "fsession" support where single BPF program is executed
upon entry and exit from traced kernel function (Menglong Dong)
- Allow bpf_timer and bpf_wq use in all programs types (Mykyta
Yatsenko, Andrii Nakryiko, Kumar Kartikeya Dwivedi, Alexei
Starovoitov)
- Make KF_TRUSTED_ARGS the default for all kfuncs and clean up their
definition across the tree (Puranjay Mohan)
- Allow BPF arena calls from non-sleepable context (Puranjay Mohan)
- Improve register id comparison logic in the verifier and extend
linked registers with negative offsets (Puranjay Mohan)
- In preparation for BPF-OOM introduce kfuncs to access memcg events
(Roman Gushchin)
- Use CFI compatible destructor kfunc type (Sami Tolvanen)
- Add bitwise tracking for BPF_END in the verifier (Tianci Cao)
- Add range tracking for BPF_DIV and BPF_MOD in the verifier (Yazhou
Tang)
- Make BPF selftests work with 64k page size (Yonghong Song)
* tag 'bpf-next-7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next: (268 commits)
selftests/bpf: Fix outdated test on storage->smap
selftests/bpf: Choose another percpu variable in bpf for btf_dump test
selftests/bpf: Remove test_task_storage_map_stress_lookup
selftests/bpf: Update task_local_storage/task_storage_nodeadlock test
selftests/bpf: Update task_local_storage/recursion test
selftests/bpf: Update sk_storage_omem_uncharge test
bpf: Switch to bpf_selem_unlink_nofail in bpf_local_storage_{map_free, destroy}
bpf: Support lockless unlink when freeing map or local storage
bpf: Prepare for bpf_selem_unlink_nofail()
bpf: Remove unused percpu counter from bpf_local_storage_map_free
bpf: Remove cgroup local storage percpu counter
bpf: Remove task local storage percpu counter
bpf: Change local_storage->lock and b->lock to rqspinlock
bpf: Convert bpf_selem_unlink to failable
bpf: Convert bpf_selem_link_map to failable
bpf: Convert bpf_selem_unlink_map to failable
bpf: Select bpf_local_storage_map_bucket based on bpf_local_storage
selftests/xsk: fix number of Tx frags in invalid packet
selftests/xsk: properly handle batch ending in the middle of a packet
bpf: Prevent reentrance into call_rcu_tasks_trace()
...
affinity of unbound kthreads (node or custom cpumask) against
housekeeping (CPU isolation) constraints and CPU hotplug events.
One crucial missing piece is the handling of cpuset: when an isolated
partition is created, deleted, or its CPUs updated, all the unbound
kthreads in the top cpuset become indifferently affine to _all_ the
non-isolated CPUs, possibly breaking their preferred affinity along
the way.
Solve this with performing the kthreads affinity update from cpuset to
the kthreads consolidated relevant code instead so that preferred
affinities are honoured and applied against the updated cpuset isolated
partitions.
The dispatch of the new isolated cpumasks to timers, workqueues and
kthreads is performed by housekeeping, as per the nice Tejun's
suggestion.
As a welcome side effect, HK_TYPE_DOMAIN then integrates both the set
from boot defined domain isolation (through isolcpus=) and cpuset
isolated partitions. Housekeeping cpumasks are now modifiable with a
specific RCU based synchronization. A big step toward making nohz_full=
also mutable through cpuset in the future.
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Merge tag 'kthread-for-7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks
Pull kthread updates from Frederic Weisbecker:
"The kthread code provides an infrastructure which manages the
preferred affinity of unbound kthreads (node or custom cpumask)
against housekeeping (CPU isolation) constraints and CPU hotplug
events.
One crucial missing piece is the handling of cpuset: when an isolated
partition is created, deleted, or its CPUs updated, all the unbound
kthreads in the top cpuset become indifferently affine to _all_ the
non-isolated CPUs, possibly breaking their preferred affinity along
the way.
Solve this with performing the kthreads affinity update from cpuset to
the kthreads consolidated relevant code instead so that preferred
affinities are honoured and applied against the updated cpuset
isolated partitions.
The dispatch of the new isolated cpumasks to timers, workqueues and
kthreads is performed by housekeeping, as per the nice Tejun's
suggestion.
As a welcome side effect, HK_TYPE_DOMAIN then integrates both the set
from boot defined domain isolation (through isolcpus=) and cpuset
isolated partitions. Housekeeping cpumasks are now modifiable with a
specific RCU based synchronization. A big step toward making
nohz_full= also mutable through cpuset in the future"
* tag 'kthread-for-7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks: (33 commits)
doc: Add housekeeping documentation
kthread: Document kthread_affine_preferred()
kthread: Comment on the purpose and placement of kthread_affine_node() call
kthread: Honour kthreads preferred affinity after cpuset changes
sched/arm64: Move fallback task cpumask to HK_TYPE_DOMAIN
sched: Switch the fallback task allowed cpumask to HK_TYPE_DOMAIN
kthread: Rely on HK_TYPE_DOMAIN for preferred affinity management
kthread: Include kthreadd to the managed affinity list
kthread: Include unbound kthreads in the managed affinity list
kthread: Refine naming of affinity related fields
PCI: Remove superfluous HK_TYPE_WQ check
sched/isolation: Remove HK_TYPE_TICK test from cpu_is_isolated()
cpuset: Remove cpuset_cpu_is_isolated()
timers/migration: Remove superfluous cpuset isolation test
cpuset: Propagate cpuset isolation update to timers through housekeeping
cpuset: Propagate cpuset isolation update to workqueue through housekeeping
PCI: Flush PCI probe workqueue on cpuset isolated partition change
sched/isolation: Flush vmstat workqueues on cpuset isolated partition change
sched/isolation: Flush memcg workqueues on cpuset isolated partition change
cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset
...
performance regressions in the recent rewrite
of the SCHED_MM_CID management code:
- Fix livelock triggered by BPF CI testing
- Fix hard lockup on weakly ordered systems
- Simplify the dropping of CIDs in the exit path
by removing an unintended transition phase.
- Fix performance/scalability regression on a
thread-pool benchmark by optimizing transitional
CIDs when scheduling out.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-urgent-2026-02-07' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler fixes from Ingo Molnar:
"Miscellaneous MMCID fixes to address bugs and performance regressions
in the recent rewrite of the SCHED_MM_CID management code:
- Fix livelock triggered by BPF CI testing
- Fix hard lockup on weakly ordered systems
- Simplify the dropping of CIDs in the exit path by removing an
unintended transition phase
- Fix performance/scalability regression on a thread-pool benchmark
by optimizing transitional CIDs when scheduling out"
* tag 'sched-urgent-2026-02-07' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/mmcid: Optimize transitional CIDs when scheduling out
sched/mmcid: Drop per CPU CID immediately when switching to per task mode
sched/mmcid: Protect transition on weakly ordered systems
sched/mmcid: Prevent live lock on task to CPU mode transition
- Fix race where sched_class operations (sched_setscheduler() and friends)
could be invoked on dead tasks after sched_ext_dead() already ran, causing
invalid SCX task state transitions and NULL pointer dereferences. This was
a regression from the cgroup exit ordering fix which moved
sched_ext_free() to finish_task_switch().
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Merge tag 'sched_ext-for-6.19-rc8-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext
Pull sched_ext fix from Tejun Heo:
- Fix race where sched_class operations (sched_setscheduler() and
friends) could be invoked on dead tasks after sched_ext_dead()
already ran, causing invalid SCX task state transitions and NULL
pointer dereferences.
This was a regression from the cgroup exit ordering fix which
moved sched_ext_free() to finish_task_switch().
* tag 'sched_ext-for-6.19-rc8-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
sched_ext: Short-circuit sched_class operations on dead tasks
7900aa699c ("sched_ext: Fix cgroup exit ordering by moving sched_ext_free()
to finish_task_switch()") moved sched_ext_free() to finish_task_switch() and
renamed it to sched_ext_dead() to fix cgroup exit ordering issues. However,
this created a race window where certain sched_class ops may be invoked on
dead tasks leading to failures - e.g. sched_setscheduler() may try to switch a
task which finished sched_ext_dead() back into SCX triggering invalid SCX task
state transitions.
Add task_dead_and_done() which tests whether a task is TASK_DEAD and has
completed its final context switch, and use it to short-circuit sched_class
operations which may be called on dead tasks.
Fixes: 7900aa699c ("sched_ext: Fix cgroup exit ordering by moving sched_ext_free() to finish_task_switch()")
Reported-by: Andrea Righi <arighi@nvidia.com>
Link: http://lkml.kernel.org/r/20260202151341.796959-1-arighi@nvidia.com
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
During the investigation of the various transition mode issues
instrumentation revealed that the amount of bitmap operations can be
significantly reduced when a task with a transitional CID schedules out
after the fixup function completed and disabled the transition mode.
At that point the mode is stable and therefore it is not required to drop
the transitional CID back into the pool. As the fixup is complete the
potential exhaustion of the CID pool is not longer possible, so the CID can
be transferred to the scheduling out task or to the CPU depending on the
current ownership mode.
The racy snapshot of mm_cid::mode which contains both the ownership state
and the transition bit is valid because runqueue lock is held and the fixup
function of a concurrent mode switch is serialized.
Assigning the ownership right there not only spares the bitmap access for
dropping the CID it also avoids it when the task is scheduled back in as it
directly hits the fast path in both modes when the CID is within the
optimal range. If it's outside the range the next schedule in will need to
converge so dropping it right away is sensible. In the good case this also
allows to go into the fast path on the next schedule in operation.
With a thread pool benchmark which is configured to cross the mode switch
boundaries frequently this reduces the number of bitmap operations by about
30% and increases the fastpath utilization in the low single digit
percentage range.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260201192835.100194627@kernel.org
When a exiting task initiates the switch from per CPU back to per task
mode, it has already dropped its CID and marked itself inactive. But a
leftover from an earlier iteration of the rework then reassigns the per
CPU CID to the exiting task with the transition bit set.
That's wrong as the task is already marked CID inactive, which means it is
inconsistent state. It's harmless because the CID is marked in transit and
therefore dropped back into the pool when the exiting task schedules out
either through preemption or the final schedule().
Simply drop the per CPU CID when the exiting task triggered the transition.
Fixes: fbd0e71dc3 ("sched/mmcid: Provide CID ownership mode fixup functions")
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260201192835.032221009@kernel.org
Shrikanth reported a hard lockup which he observed once. The stack trace
shows the following CID related participants:
watchdog: CPU 23 self-detected hard LOCKUP @ mm_get_cid+0xe8/0x188
NIP: mm_get_cid+0xe8/0x188
LR: mm_get_cid+0x108/0x188
mm_cid_switch_to+0x3c4/0x52c
__schedule+0x47c/0x700
schedule_idle+0x3c/0x64
do_idle+0x160/0x1b0
cpu_startup_entry+0x48/0x50
start_secondary+0x284/0x288
start_secondary_prolog+0x10/0x14
watchdog: CPU 11 self-detected hard LOCKUP @ plpar_hcall_norets_notrace+0x18/0x2c
NIP: plpar_hcall_norets_notrace+0x18/0x2c
LR: queued_spin_lock_slowpath+0xd88/0x15d0
_raw_spin_lock+0x80/0xa0
raw_spin_rq_lock_nested+0x3c/0xf8
mm_cid_fixup_cpus_to_tasks+0xc8/0x28c
sched_mm_cid_exit+0x108/0x22c
do_exit+0xf4/0x5d0
make_task_dead+0x0/0x178
system_call_exception+0x128/0x390
system_call_vectored_common+0x15c/0x2ec
The task on CPU11 is running the CID ownership mode change fixup function
and is stuck on a runqueue lock. The task on CPU23 is trying to get a CID
from the pool with the same runqueue lock held, but the pool is empty.
After decoding a similar issue in the opposite direction switching from per
task to per CPU mode the tool which models the possible scenarios failed to
come up with a similar loop hole.
This showed up only once, was not reproducible and according to tooling not
related to a overlooked scheduling scenario permutation. But the fact that
it was observed on a PowerPC system gave the right hint: PowerPC is a
weakly ordered architecture.
The transition mechanism does:
WRITE_ONCE(mm->mm_cid.transit, MM_CID_TRANSIT);
WRITE_ONCE(mm->mm_cid.percpu, new_mode);
fixup()
WRITE_ONCE(mm->mm_cid.transit, 0);
mm_cid_schedin() does:
if (!READ_ONCE(mm->mm_cid.percpu))
...
cid |= READ_ONCE(mm->mm_cid.transit);
so weakly ordered systems can observe percpu == false and transit == 0 even
if the fixup function has not yet completed. As a consequence the task will
not drop the CID when scheduling out before the fixup is completed, which
means the CID space can be exhausted and the next task scheduling in will
loop in mm_get_cid() and the fixup thread can livelock on the held runqueue
lock as above.
This could obviously be solved by using:
smp_store_release(&mm->mm_cid.percpu, true);
and
smp_load_acquire(&mm->mm_cid.percpu);
but that brings a memory barrier back into the scheduler hotpath, which was
just designed out by the CID rewrite.
That can be completely avoided by combining the per CPU mode and the
transit storage into a single mm_cid::mode member and ordering the stores
against the fixup functions to prevent the CPU from reordering them.
That makes the update of both states atomic and a concurrent read observes
always consistent state.
The price is an additional AND operation in mm_cid_schedin() to evaluate
the per CPU or the per task path, but that's in the noise even on strongly
ordered architectures as the actual load can be significantly more
expensive and the conditional branch evaluation is there anyway.
Fixes: fbd0e71dc3 ("sched/mmcid: Provide CID ownership mode fixup functions")
Closes: https://lore.kernel.org/bdfea828-4585-40e8-8835-247c6a8a76b0@linux.ibm.com
Reported-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260201192834.965217106@kernel.org
Ihor reported a BPF CI failure which turned out to be a live lock in the
MM_CID management. The scenario is:
A test program creates the 5th thread, which means the MM_CID users become
more than the number of CPUs (four in this example), so it switches to per
CPU ownership mode.
At this point each live task of the program has a CID associated. Assume
thread creation order assignment for simplicity.
T0 CID0 runs fork() and creates T4
T1 CID1
T2 CID2
T3 CID3
T4 --- not visible yet
T0 sets mm_cid::percpu = true and transfers its own CID to CPU0 where it
runs on and then starts the fixup which walks through the threads to
transfer the per task CIDs either to the CPU the task is running on or drop
it back into the pool if the task is not on a CPU.
During that T1 - T3 are free to schedule in and out before the fixup caught
up with them. Going through all possible permutations with a python script
revealed a few problematic cases. The most trivial one is:
T1 schedules in on CPU1 and observes percpu == true, so it transfers
its CID to CPU1
T1 is migrated to CPU2 and schedule in observes percpu == true, but
CPU2 does not have a CID associated and T1 transferred its own to
CPU1
So it has to allocate one with CPU2 runqueue lock held, but the
pool is empty, so it keeps looping in mm_get_cid().
Now T0 reaches T1 in the thread walk and tries to lock the corresponding
runqueue lock, which is held causing a full live lock.
There is a similar scenario in the reverse direction of switching from per
CPU to task mode which is way more obvious and got therefore addressed by
an intermediate mode. In this mode the CIDs are marked with MM_CID_TRANSIT,
which means that they are neither owned by the CPU nor by the task. When a
task schedules out with a transit CID it drops the CID back into the pool
making it available for others to use temporarily. Once the task which
initiated the mode switch finished the fixup it clears the transit mode and
the process goes back into per task ownership mode.
Unfortunately this insight was not mapped back to the task to CPU mode
switch as the above described scenario was not considered in the analysis.
Apply the same transit mechanism to the task to CPU mode switch to handle
these problematic cases correctly.
As with the CPU to task transition this results in a potential temporary
contention on the CID bitmap, but that's only for the time it takes to
complete the transition. After that it stays in steady mode which does not
touch the bitmap at all.
Fixes: fbd0e71dc3 ("sched/mmcid: Provide CID ownership mode fixup functions")
Closes: https://lore.kernel.org/2b7463d7-0f58-4e34-9775-6e2115cfb971@linux.dev
Reported-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260201192834.897115238@kernel.org
When cpuset isolated partitions get updated, unbound kthreads get
indifferently affine to all non isolated CPUs, regardless of their
individual affinity preferences.
For example kswapd is a per-node kthread that prefers to be affine to
the node it refers to. Whenever an isolated partition is created,
updated or deleted, kswapd's node affinity is going to be broken if any
CPU in the related node is not isolated because kswapd will be affine
globally.
Fix this with letting the consolidated kthread managed affinity code do
the affinity update on behalf of cpuset.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Marco Crivellari <marco.crivellari@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Waiman Long <longman@redhat.com>
Cc: cgroups@vger.kernel.org
Until now, cpuset would propagate isolated partition changes to
timer migration so that unbound timers don't get migrated to isolated
CPUs.
Since housekeeping now centralizes, synchronize and propagates isolation
cpumask changes, perform the work from that subsystem for consolidation
and consistency purposes.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Until now, cpuset would propagate isolated partition changes to
workqueues so that unbound workers get properly reaffined.
Since housekeeping now centralizes, synchronize and propagates isolation
cpumask changes, perform the work from that subsystem for consolidation
and consistency purposes.
For simplification purpose, the target function is adapted to take the
new housekeeping mask instead of the isolated mask.
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: "Michal Koutný" <mkoutny@suse.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Marco Crivellari <marco.crivellari@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Waiman Long <longman@redhat.com>
Cc: cgroups@vger.kernel.org
The HK_TYPE_DOMAIN housekeeping cpumask is now modifiable at runtime. In
order to synchronize against PCI probe works and make sure that no
asynchronous probing is still pending or executing on a newly isolated
CPU, the housekeeping subsystem must flush the PCI probe works.
However the PCI probe works can't be flushed easily since they are
queued to the main per-CPU workqueue pool.
Solve this with creating a PCI probe-specific pool and provide and use
the appropriate flushing API.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Marco Crivellari <marco.crivellari@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Waiman Long <longman@redhat.com>
Cc: linux-pci@vger.kernel.org
The HK_TYPE_DOMAIN housekeeping cpumask is now modifiable at runtime.
In order to synchronize against vmstat workqueue to make sure
that no asynchronous vmstat work is still pending or executing on a
newly made isolated CPU, the housekeeping susbsystem must flush the
vmstat workqueues.
This involves flushing the whole mm_percpu_wq workqueue, shared with
LRU drain, introducing here a welcome side effect.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Marco Crivellari <marco.crivellari@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Waiman Long <longman@redhat.com>
Cc: linux-mm@kvack.org
The HK_TYPE_DOMAIN housekeeping cpumask is now modifiable at runtime. In
order to synchronize against memcg workqueue to make sure that no
asynchronous draining is still pending or executing on a newly made
isolated CPU, the housekeeping susbsystem must flush the memcg
workqueues.
However the memcg workqueues can't be flushed easily since they are
queued to the main per-CPU workqueue pool.
Solve this with creating a memcg specific pool and provide and use the
appropriate flushing API.
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Marco Crivellari <marco.crivellari@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Waiman Long <longman@redhat.com>
Cc: cgroups@vger.kernel.org
Cc: linux-mm@kvack.org
Until now, HK_TYPE_DOMAIN used to only include boot defined isolated
CPUs passed through isolcpus= boot option. Users interested in also
knowing the runtime defined isolated CPUs through cpuset must use
different APIs: cpuset_cpu_is_isolated(), cpu_is_isolated(), etc...
There are many drawbacks to that approach:
1) Most interested subsystems want to know about all isolated CPUs, not
just those defined on boot time.
2) cpuset_cpu_is_isolated() / cpu_is_isolated() are not synchronized with
concurrent cpuset changes.
3) Further cpuset modifications are not propagated to subsystems
Solve 1) and 2) and centralize all isolated CPUs within the
HK_TYPE_DOMAIN housekeeping cpumask.
Subsystems can rely on RCU to synchronize against concurrent changes.
The propagation mentioned in 3) will be handled in further patches.
[Chen Ridong: Fix cpu_hotplug_lock deadlock and use correct static
branch API]
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Chen Ridong <chenridong@huawei.com>
Signed-off-by: Chen Ridong <chenridong@huawei.com>
Cc: "Michal Koutný" <mkoutny@suse.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Marco Crivellari <marco.crivellari@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Waiman Long <longman@redhat.com>
Cc: cgroups@vger.kernel.org
HK_TYPE_DOMAIN's cpumask will soon be made modifiable by cpuset.
A synchronization mechanism is then needed to synchronize the updates
with the housekeeping cpumask readers.
Turn the housekeeping cpumasks into RCU pointers. Once a housekeeping
cpumask will be modified, the update side will wait for an RCU grace
period and propagate the change to interested subsystem when deemed
necessary.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Marco Crivellari <marco.crivellari@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Waiman Long <longman@redhat.com>
HK_TYPE_DOMAIN will soon integrate not only boot defined isolcpus= CPUs
but also cpuset isolated partitions.
Housekeeping still needs a way to record what was initially passed
to isolcpus= in order to keep these CPUs isolated after a cpuset
isolated partition is modified or destroyed while containing some of
them.
Create a new HK_TYPE_DOMAIN_BOOT to keep track of those.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Marco Crivellari <marco.crivellari@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Waiman Long <longman@redhat.com>
Consider the following sequence on a CPU configured with nohz_full:
1) A task P runs in cgroup A, and cgroup A becomes throttled due to CFS
bandwidth control. The gse (cgroup A) where the task P attached is
dequeued and the CPU switches to idle.
2) Before cgroup A is unthrottled, task P is migrated from cgroup A to
another cgroup B (not throttled).
During sched_move_task(), the task P is observed as queued but not
running, and therefore no resched_curr() is triggered.
3) Since the CPU is nohz_full, it remains in do_idle() waiting for an
explicit scheduling event, i.e., resched_curr().
4) For kernel <= 5.10: Later, cgroup A is unthrottled. However, the task
P has already been migrated out of cgroup A, so unthrottle_cfs_rq()
may observe load_weight == 0 and return early without resched_curr()
called. For kernel >= 6.6: The unthrottling path normally triggers
`resched_curr()` almost cases even when no runnable tasks remain in the
unthrottled cgroup, preventing the idle stall described above. However,
if cgroup A is removed before it gets unthrottled, the unthrottling path
for cgroup A is never executed. In a result, no `resched_curr()` can be
called.
5) At this point, the task P is runnable in cgroup B (not throttled), but
the CPU remains in do_idle() with no pending reschedule point. The
system stays in this state until an unrelated event (e.g. a new task
wakeup or any cases) that can trigger a resched_curr() breaks the
nohz_full idle state, and then the task P finally gets scheduled.
The root cause is that sched_move_task() may classify the task as only
queued, not running, and therefore fails to trigger a resched_curr(),
while the later unthrottling path no longer has visibility of the
migrated task.
Preserve the existing behavior for running tasks by issuing
resched_curr(), and explicitly invoke check_preempt_curr() for tasks
that were queued at the time of migration. This ensures that runnable
tasks are reconsidered for scheduling even when nohz_full suppresses
periodic ticks.
Fixes: 29f59db3a7 ("sched: group-scheduler core")
Signed-off-by: Zicheng Qu <quzicheng@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: Aaron Lu <ziqianlu@bytedance.com>
Tested-by: Aaron Lu <ziqianlu@bytedance.com>
Link: https://patch.msgid.link/20260130083438.1122457-1-quzicheng@huawei.com
Use %pe format specifier for printing PTR_ERR() error values
to make error messages more readable.
Found by Coccinelle:
./cpufreq_schedutil.c:685:49-56: WARNING: Consider using %pe to print PTR_ERR()
Signed-off-by: zenghongling <zenghongling@kylinos.cn>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260120083333.148385-1-zenghongling@kylinos.cn
CPU0 becomes overloaded when hosting a CPU-bound RT task, a non-CPU-bound
RT task, and a CFS task stuck in kernel space. When other CPUs switch from
RT to non-RT tasks, RT load balancing (LB) is triggered; with
HAVE_RT_PUSH_IPI enabled, they send IPIs to CPU0 to drive the execution
of rto_push_irq_work_func. During push_rt_task on CPU0,
if next_task->prio < rq->donor->prio, resched_curr() sets NEED_RESCHED
and after the push operation completes, CPU0 calls rto_next_cpu().
Since only CPU0 is overloaded in this scenario, rto_next_cpu() should
ideally return -1 (no further IPI needed).
However, multiple CPUs invoking tell_cpu_to_push() during LB increments
rd->rto_loop_next. Even when rd->rto_cpu is set to -1, the mismatch between
rd->rto_loop and rd->rto_loop_next forces rto_next_cpu() to restart its
search from -1. With CPU0 remaining overloaded (satisfying rt_nr_migratory
&& rt_nr_total > 1), it gets reselected, causing CPU0 to queue irq_work to
itself and send self-IPIs repeatedly. As long as CPU0 stays overloaded and
other CPUs run pull_rt_tasks(), it falls into an infinite self-IPI loop,
which triggers a CPU hardlockup due to continuous self-interrupts.
The trigging scenario is as follows:
cpu0 cpu1 cpu2
pull_rt_task
tell_cpu_to_push
<------------irq_work_queue_on
rto_push_irq_work_func
push_rt_task
resched_curr(rq) pull_rt_task
rto_next_cpu tell_cpu_to_push
<-------------------------- atomic_inc(rto_loop_next)
rd->rto_loop != next
rto_next_cpu
irq_work_queue_on
rto_push_irq_work_func
Fix redundant self-IPI by filtering the initiating CPU in rto_next_cpu().
This solution has been verified to effectively eliminate spurious self-IPIs
and prevent CPU hardlockup scenarios.
Fixes: 4bdced5c9a ("sched/rt: Simplify the IPI based RT balancing logic")
Suggested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Suggested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Chen Jinghuang <chenjinghuang2@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Link: https://patch.msgid.link/20260122012533.673768-1-chenjinghuang2@huawei.com
Read-mostly sched_clock_irqtime may share the same cacheline with
frequently updated nohz struct. Make it as static_key to avoid
false sharing issue.
The only user of disable_sched_clock_irqtime()
is tsc_.*mark_unstable() which may be invoked under atomic context
and require a workqueue to disable static_key. But both of them
calls clear_sched_clock_stable() just before doing
disable_sched_clock_irqtime(). We can reuse
"sched_clock_work" to also disable sched_clock_irqtime().
One additional case need to handle is if the tsc is marked unstable
before late_initcall() phase, sched_clock_work will not be invoked
and sched_clock_irqtime will stay enabled although clock is unstable:
tsc_init()
enable_sched_clock_irqtime() # irqtime accounting is enabled here
...
if (unsynchronized_tsc()) # true
mark_tsc_unstable()
clear_sched_clock_stable()
__sched_clock_stable_early = 0;
...
if (static_key_count(&sched_clock_running.key) == 2)
# Only happens at sched_clock_init_late()
__clear_sched_clock_stable(); # Never executed
...
# late_initcall() phase
sched_clock_init_late()
if (__sched_clock_stable_early) # Already false
__set_sched_clock_stable(); # sched_clock is never marked stable
# TSC unstable, but sched_clock_work won't run to disable irqtime
So we need to disable_sched_clock_irqtime() in sched_clock_init_late()
if clock is unstable.
Reported-by: Benjamin Lei <benjamin.lei@intel.com>
Suggested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Wangyang Guo <wangyang.guo@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Reviewed-by: Tianyou Li <tianyou.li@intel.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://patch.msgid.link/20260127072509.2627346-1-wangyang.guo@intel.com
There are two problems with sched_server_write_common() that can cause the
dl_server to malfunction upon attempting to change the parameters:
1) when, after having disabled the dl_server by setting runtime=0, it is
enabled again while tasks are already enqueued. In this case is_active would
still be 0 and dl_server_start() would not be called.
2) when dl_server_apply_params() would fail, runtime is not applied and does
not reflect the new state.
Instead have dl_server_start() check its actual dl_runtime, and have
sched_server_write_common() unconditionally (re)start the dl_server. It will
automatically stop if there isn't anything to do, so spurious activation is
harmless -- while failing to start it is a problem.
While there, move the printk out of the locked region and make it symmetric,
also printing on enable.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260203103407.GK1282955@noisy.programming.kicks-ass.net
When a sched_ext server is loaded, tasks in the fair class are
automatically moved to the sched_ext class. Add support to modify the
ext server parameters similar to how the fair server parameters are
modified.
Re-use common code between ext and fair servers as needed.
Co-developed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260126100050.3854740-6-arighi@nvidia.com
sched_ext currently suffers starvation due to RT. The same workload when
converted to EXT can get zero runtime if RT is 100% running, causing EXT
processes to stall. Fix it by adding a DL server for EXT.
A kselftest is also included later to confirm that both DL servers are
functioning correctly:
# ./runner -t rt_stall
===== START =====
TEST: rt_stall
DESCRIPTION: Verify that RT tasks cannot stall SCHED_EXT tasks
OUTPUT:
TAP version 13
1..1
# Runtime of FAIR task (PID 1511) is 0.250000 seconds
# Runtime of RT task (PID 1512) is 4.750000 seconds
# FAIR task got 5.00% of total runtime
ok 1 PASS: FAIR task got more than 4.00% of runtime
TAP version 13
1..1
# Runtime of EXT task (PID 1514) is 0.250000 seconds
# Runtime of RT task (PID 1515) is 4.750000 seconds
# EXT task got 5.00% of total runtime
ok 2 PASS: EXT task got more than 4.00% of runtime
TAP version 13
1..1
# Runtime of FAIR task (PID 1517) is 0.250000 seconds
# Runtime of RT task (PID 1518) is 4.750000 seconds
# FAIR task got 5.00% of total runtime
ok 3 PASS: FAIR task got more than 4.00% of runtime
TAP version 13
1..1
# Runtime of EXT task (PID 1521) is 0.250000 seconds
# Runtime of RT task (PID 1522) is 4.750000 seconds
# EXT task got 5.00% of total runtime
ok 4 PASS: EXT task got more than 4.00% of runtime
ok 1 rt_stall #
===== END =====
Co-developed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260126100050.3854740-5-arighi@nvidia.com
Currently the DL server interface for applying parameters checks
CFS-internals to identify if the server is active. This is error-prone
and makes it difficult when adding new servers in the future.
Fix it, by using dl_server_active() which is also used by the DL server
code to determine if the DL server was started.
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Tejun Heo <tj@kernel.org>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260126100050.3854740-4-arighi@nvidia.com
Updating "ppos" on error conditions does not make much sense. The pattern
is to return the error code directly without modifying the position, or
modify the position on success and return the number of bytes written.
Since on success, the return value of apply is 0, there is no point in
modifying ppos either. Fix it by removing all this and just returning
error code or number of bytes written on success.
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Tejun Heo <tj@kernel.org>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260126100050.3854740-3-arighi@nvidia.com
The defer params were not cleared in __dl_clear_params. Clear them.
Without this is some of my test cases are flaking and the DL timer is
not starting correctly AFAICS.
Fixes: a110a81c52 ("sched/deadline: Deferrable dl server")
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260126100050.3854740-2-arighi@nvidia.com
Problem
=======
Commit 658eb5ab91 ("delayacct: add delay max to record delay peak")
introduced the delay max for getdelays, which records abnormal latency
peaks and helps us understand the magnitude of such delays. However, the
peak latency value alone is insufficient for effective root cause
analysis. Without the precise timestamp of when the peak occurred, we
still lack the critical context needed to correlate it with other system
events.
Solution
========
To address this, we need to additionally record a precise timestamp when
the maximum latency occurs. By correlating this timestamp with system
logs and monitoring metrics, we can identify processes with abnormal
resource usage at the same moment, which can help us to pinpoint root
causes.
Use Case
========
bash-4.4# ./getdelays -d -t 227
print delayacct stats ON
TGID 227
CPU count real total virtual total delay total delay average delay max delay min delay max timestamp
46 188000000 192348334 4098012 0.089ms 0.429260ms 0.051205ms 2026-01-15T15:06:58
IO count delay total delay average delay max delay min delay max timestamp
0 0 0.000ms 0.000000ms 0.000000ms N/A
SWAP count delay total delay average delay max delay min delay max timestamp
0 0 0.000ms 0.000000ms 0.000000ms N/A
RECLAIM count delay total delay average delay max delay min delay max timestamp
0 0 0.000ms 0.000000ms 0.000000ms N/A
THRAS HING count delay total delay average delay max delay min delay max timestamp
0 0 0.000ms 0.000000ms 0.000000ms N/A
COMPACT count delay total delay average delay max delay min delay max timestamp
0 0 0.000ms 0.000000ms 0.000000ms N/A
WPCOPY count delay total delay average delay max delay min delay max timestamp
182 19413338 0.107ms 0.547353ms 0.022462ms 2026-01-15T15:05:24
IRQ count delay total delay average delay max delay min delay max timestamp
0 0 0.000ms 0.000000ms 0.000000ms N/A
Link: https://lkml.kernel.org/r/20260119100241520gWubW8-5QfhSf9gjqcc_E@zte.com.cn
Signed-off-by: Wang Yaxin <wang.yaxin@zte.com.cn>
Cc: Fan Yu <fan.yu9@zte.com.cn>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Andrea reported the dl_server getting stuck for him. He tracked it
down to a state where dl_server_start() saw dl_defer_running==1, but
the dl_server's job is no longer valid at the time of
dl_server_start().
In the state diagram this corresponds to [4] D->A (or dl_server_stop()
due to no more runnable tasks) followed by [1], which in case of a
lapsed deadline must then be A->B.
Now our A has dl_defer_running==1, while B demands
dl_defer_running==0, therefore it must get cleared when the CBS wakeup
rules demand a replenish.
Fixes: a110a81c52 ("sched/deadline: Deferrable dl server")
Reported-by: Andrea Righi arighi@nvidia.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Tested-by: Andrea Righi arighi@nvidia.com
Link: https://lkml.kernel.org/r/20260123161645.2181752-1-arighi@nvidia.com
Link: https://patch.msgid.link/20260130124100.GC1079264@noisy.programming.kicks-ass.net
This agressively bypasses run_to_parity and slice protection with the
assumpiton that this is what waker wants but there is no garantee that
the wakee will be the next to run. It is a better choice to use
yield_to_task or WF_SYNC in such case.
This increases the number of resched and preemption because a task becomes
quickly "ineligible" when it runs; We update the task vruntime periodically
and before the task exhausted its slice or at least quantum.
Example:
2 tasks A and B wake up simultaneously with lag = 0. Both are
eligible. Task A runs 1st and wakes up task C. Scheduler updates task
A's vruntime which becomes greater than average runtime as all others
have a lag == 0 and didn't run yet. Now task A is ineligible because
it received more runtime than the other task but it has not yet
exhausted its slice nor a min quantum. We force preemption, disable
protection but Task B will run 1st not task C.
Sidenote, DELAY_ZERO increases this effect by clearing positive lag at
wake up.
Fixes: e837456fdc ("sched/fair: Reimplement NEXT_BUDDY to align with EEVDF goals")
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260123102858.52428-1-vincent.guittot@linaro.org
NEXT_BUDDY was disabled with the introduction of EEVDF and enabled again
after NEXT_BUDDY was rewritten for EEVDF by commit e837456fdc ("sched/fair:
Reimplement NEXT_BUDDY to align with EEVDF goals"). It was not expected
that this would be a universal win without a crystal ball instruction
but the reported regressions are a concern [1][2] even if gains were
also reported. Specifically;
o mysql with client/server running on different servers regresses
o specjbb reports lower peak metrics
o daytrader regresses
The mysql is realistic and a concern. It needs to be confirmed if
specjbb is simply shifting the point where peak performance is measured
but still a concern. daytrader is considered to be representative of a
real workload.
Access to test machines is currently problematic for verifying any fix to
this problem. Disable NEXT_BUDDY for now by default until the root causes
are addressed.
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Link: https://lore.kernel.org/lkml/4b96909a-f1ac-49eb-b814-97b8adda6229@arm.com [1]
Link: https://lore.kernel.org/lkml/ec3ea66f-3a0d-4b5a-ab36-ce778f159b5b@linux.ibm.com [2]
Link: https://patch.msgid.link/fyqsk63pkoxpeaclyqsm5nwtz3dyejplr7rg6p74xwemfzdzuu@7m7xhs5aqpqw
Currently, rq->idle_stamp is only used to calculate avg_idle during
wakeups. This means other paths that move a task to an idle CPU such as
fork/clone, execve, or migrations, do not end the CPU's idle status in
the scheduler's eyes, leading to an inaccurate avg_idle.
This patch introduces update_rq_avg_idle() to provide a more accurate
measurement of CPU idle duration. By invoking this helper in
put_prev_task_idle(), we ensure avg_idle is updated whenever a CPU
stops being idle, regardless of how the new task arrived.
Testing on an 80-core Ampere Altra (ARMv8) with 6.19-rc5 baseline:
- Hackbench : +7.2% performance gain at 16 threads.
- Schbench: Reduced p99.9 tail latencies at high concurrency.
Signed-off-by: Shubhang Kaushik <shubhang@os.amperecomputing.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: Shubhang Kaushik <shubhang@os.amperecomputing.com>
Link: https://patch.msgid.link/20260121-v8-patch-series-v8-1-b7f1cbee5055@os.amperecomputing.com
Using kstrtouint_from_user() instead of copy_from_user() + kstrtouint()
makes the code simpler and less error-prone.
Suggested-by: Yury Norov <ynorov@nvidia.com>
Signed-off-by: Fushuai Wang <wangfushuai@baidu.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Yury Norov <ynorov@nvidia.com>
Link: https://patch.msgid.link/20260117145615.53455-2-fushuai.wang@linux.dev
nohz.nr_cpus was observed as contended cacheline when running
enterprise workload on large systems.
Fundamental scalability challenge with nohz.idle_cpus_mask
and nohz.nr_cpus is the following:
(1) nohz_balancer_kick() observes (reads) nohz.nr_cpus
(or nohz.idle_cpu_mask) and nohz.has_blocked to see whether there's
any nohz balancing work to do, in every scheduler tick.
(2) nohz_balance_enter_idle() and nohz_balance_exit_idle()
(through nohz_balancer_kick() via sched_tick()) modify (write)
nohz.nr_cpus (and/or nohz.idle_cpu_mask) and nohz.has_blocked.
The characteristic frequencies are the following:
(1) nohz_balancer_kick() happens at scheduler (busy)tick frequency
on CPU(which has not gone idle). This is a relatively constant
frequency in the ~1 kHz range or lower.
(2) happens at idle enter/exit frequency on every CPU that goes to idle.
This is workload dependent, but can easily be hundreds of kHz for
IO-bound loads and high CPU counts. Ie. can be orders of magnitude
higher than (1), in which case a cachemiss at every invocation of (1)
is almost inevitable. idle exit will trigger (1) on the CPU
which is coming out of idle.
There's two types of costs from these functions:
(A) scheduler tick cost via (1): this happens on busy CPUs too, and is
thus a primary scalability cost. But the rate here is constant and
typically much lower than (B), hence the absolute benefit to workload
scalability will be lower as well.
(B) idle cost via (2): going-to-idle and coming-from-idle costs are
secondary concerns, because they impact power efficiency more than
they impact scalability. But in terms of absolute cost this scales
up with nr_cpus as well, and a much faster rate, and thus may also
approach and negatively impact system limits like
memory bus/fabric bandwidth.
Note that nohz.idle_cpus_mask and nohz.nr_cpus may appear to reside in the
same cacheline, however under CONFIG_CPUMASK_OFFSTACK=y the backing storage
for nohz.idle_cpus_mask will be elsewhere. With CPUMASK_OFFSTACK=n,
the nohz.idle_cpus_mask and rest of nohz fields are in different cachelines
under typical NR_CPUS=512/2048. This implies two separate cachelines
being dirtied upon idle entry / exit.
nohz.nr_cpus can be derived from the mask itself. Its usage doesn't warrant
a functionally correct value. This means one less cacheline being dirtied in
idle entry/exit path which helps to save some bus bandwidth w.r.t to those
nohz functions(approx 50%). This in turn helps to improve enterprise
workload throughput.
On system with 480 CPUs, running "hackbench 40 process 10000 loops"
(Avg of 3 runs)
baseline:
0.81% hackbench [k] nohz_balance_exit_idle
0.21% hackbench [k] nohz_balancer_kick
0.09% swapper [k] nohz_run_idle_balance
With patch:
0.35% hackbench [k] nohz_balance_exit_idle
0.09% hackbench [k] nohz_balancer_kick
0.07% swapper [k] nohz_run_idle_balance
[Ingo Molnar: scalability analysis changlog]
Reviewed-and-tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://patch.msgid.link/20260115073524.376643-4-sshegde@linux.ibm.com
These days most of the system have multi cores. The likelyhood of
at least one or more CPUs in nohz (idle state) is higher.
Give accurate hint to the branch predictor.
Reviewed-and-tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://patch.msgid.link/20260115073524.376643-3-sshegde@linux.ibm.com
Current code does.
- Read nohz.nr_cpus
- Check if the time has passed to do NOHZ idle balance
Instead do this.
- Check if the time has passed to do NOHZ idle balance
- Read nohz.nr_cpus
This will skip the read most of the time in normal system usage.
i.e when there are nohz.nr_cpus (system is not 100% busy).
Note that when there are no idle CPUs(100% busy), even if the flag gets
set to NOHZ_STATS_KICK | NOHZ_NEXT_KICK, find_new_ilb will fail and
there will be no NOHZ idle balance. In such cases there will be a very
narrow window where, kick_ilb will be called un-necessarily.
However current functionality is still retained.
Note: This patch doesn't solve any cacheline overheads. No improvement
in performance apart from saving a few cycles of reading nohz.nr_cpus
Reviewed-and-tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://patch.msgid.link/20260115073524.376643-2-sshegde@linux.ibm.com
The avg_vruntime comment contains a couple of mathematical notation
issues:
- The summation over w_i * (V - v_i) is written in an ambiguous form
- The delta term refers to v instead of v0, which is inconsistent
with the code and preceding explanation
Fix these to make the comment mathematically correct and consistent
with the implementation.
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260114090035.19033-1-zhanxusheng@xiaomi.com
Commit adcc3bfa88 ("sched: Adapt sched tracepoints for RV task model")
added a tracepoint to the need_resched action that can be triggered also
by set_tsk_need_resched.
This function was previously accessible from out-of-tree modules but
it's no longer available because the __trace_set_need_resched() symbol
is not exported (together with the tracepoint itself, which was exported
in a separate patch) and building such modules fails.
Export __trace_set_need_resched to modules to fix those build issues.
Fixes: adcc3bfa88 ("sched: Adapt sched tracepoints for RV task model")
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Link: https://patch.msgid.link/20260112140413.362202-1-gmonaco@redhat.com
Pierre reported hitting balance callback warnings for deadline tasks
after commit 6455ad5346 ("sched: Move sched_class::prio_changed()
into the change pattern").
It turns out that DEQUEUE_SAVE+ENQUEUE_RESTORE does not preserve DL
priority and subsequently trips a balance pass -- where one was not
expected.
From discussion with Juri and Luca, the purpose of this clause was to
deal with tasks new to DL and all those sites will have MOVE set (as
well as CLASS, but MOVE is move conservative at this point).
Per the previous patches MOVE is audited to always run the balance
callbacks, so switch enqueue_dl_entity() to use MOVE for this case.
Fixes: 6455ad5346 ("sched: Move sched_class::prio_changed() into the change pattern")
Reported-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Pierre Gondois <pierre.gondois@arm.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://patch.msgid.link/20260114130528.GB831285@noisy.programming.kicks-ass.net
While FIFO/RR have static priority, DEADLINE is a dynamic priority
scheme. Notably it has static priority -1. Do not assume the priority
doesn't change for deadline tasks just because the static priority
doesn't change.
This ensures DL always sees {DE,EN}QUEUE_MOVE where appropriate.
Fixes: ff77e46853 ("sched/rt: Fix PI handling vs. sched_setscheduler()")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Pierre Gondois <pierre.gondois@arm.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://patch.msgid.link/20260114130528.GB831285@noisy.programming.kicks-ass.net
The {DE,EN}QUEUE_MOVE flag indicates a task is allowed to change
priority, which means there could be balance callbacks queued.
Therefore audit all MOVE users and make sure they do run balance
callbacks before dropping rq-lock.
Fixes: 6455ad5346 ("sched: Move sched_class::prio_changed() into the change pattern")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Pierre Gondois <pierre.gondois@arm.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://patch.msgid.link/20260114130528.GB831285@noisy.programming.kicks-ass.net
When setup_new_dl_entity() is called from enqueue_task_dl() ->
enqueue_dl_entity(), the rq-clock should already be updated, and
calling update_rq_clock() again is not right.
Move the update_rq_clock() to the one other caller of
setup_new_dl_entity(): sched_init_dl_server().
Fixes: 9f239df555 ("sched/deadline: Initialize dl_servers after SMP")
Reported-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Pierre Gondois <pierre.gondois@arm.com>
Link: https://patch.msgid.link/20260113115622.GA831285@noisy.programming.kicks-ass.net
Pratheek tripped a WARN and noted the following issue:
> Inspecting the set of events that led to the warning being triggered
> showed the following:
>
> systemd-1 [008] dN.31 ...: do_set_cpus_allowed: set_cpus_allowed begin!
>
> systemd-1 [008] dN.31 ...: sched_change_begin: Begin!
> systemd-1 [008] dN.31 ...: sched_change_begin: Before dequeue_task()!
> systemd-1 [008] dN.31 ...: update_curr_dl_se: update_curr_dl_se: ENQUEUE_REPLENISH
> systemd-1 [008] dN.31 ...: enqueue_dl_entity: enqueue_dl_entity: ENQUEUE_REPLENISH
> systemd-1 [008] dN.31 ...: replenish_dl_entity: Replenish before: 14815760217
> systemd-1 [008] dN.31 ...: replenish_dl_entity: Replenish after: 14816960047
> systemd-1 [008] dN.31 ...: sched_change_begin: Before put_prev_task()!
>
> systemd-1 [008] dN.31 ...: sched_change_end: Before enqueue_task()!
> systemd-1 [008] dN.31 ...: sched_change_end: Before put_prev_task()!
> systemd-1 [008] dN.31 ...: prio_changed_dl: Queuing pull task on prio change: 14815760217 -> 14816960047
> systemd-1 [008] dN.31 ...: prio_changed_dl: Queuing balance callback!
> systemd-1 [008] dN.31 ...: sched_change_end: End!
>
> systemd-1 [008] dN.31 ...: do_set_cpus_allowed: set_cpus_allowed end!
> systemd-1 [008] dN.21 ...: __schedule: Woops! Balance callback found!
>
> 1. sched_change_begin() from guard(sched_change) in
> do_set_cpus_allowed() stashes the priority, which for the deadline
> task, is "p->dl.deadline".
> 2. The dequeue of the deadline task replenishes the deadline.
> 3. The task is enqueued back after guard's scope ends and since there is
> no *_CLASS flags set, sched_change_end() calls
> dl_sched_class->prio_changed() which compares the deadline.
> 4. Since deadline was moved on dequeue, prio_changed_dl() sees the value
> differ from the stashed value and queues a balance pull callback.
> 5. do_set_cpus_allowed() finishes and drops the rq_lock without doing a
> do_balance_callbacks().
> 6. Grabbing the rq_lock() at subsequent __schedule() triggers the
> warning since the balance pull callback was never executed before
> dropping the lock.
Meaning get_prio_dl() ought to update current and return an up-to-date
value.
Fixes: 6455ad5346 ("sched: Move sched_class::prio_changed() into the change pattern")
Reported-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://patch.msgid.link/20260106104113.GX3707891@noisy.programming.kicks-ass.net
Cross-merge BPF and other fixes after downstream PR.
No conflicts.
Adjacent:
Auto-merging MAINTAINERS
Auto-merging Makefile
Auto-merging kernel/bpf/verifier.c
Auto-merging kernel/sched/ext.c
Auto-merging mm/memcontrol.c
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
The tracepoints sched_entry, sched_exit and sched_set_need_resched
are not exported to tracefs as trace events, this allows only kernel
code to access them. Helper modules like [1] can be used to still have
the tracepoints available to ftrace for debugging purposes, but they do
rely on the tracepoints being exported.
Export the 3 not exported tracepoints.
Note that sched_set_state is already exported as the macro is called
from modules.
[1] - https://github.com/qais-yousef/sched_tp.git
Fixes: adcc3bfa88 ("sched: Adapt sched tracepoints for RV task model")
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Link: https://patch.msgid.link/20251205131621.135513-9-gmonaco@redhat.com
The deadline server can currently stop due to idle although fair tasks
are runnable. This happens essentially when:
* the server is set to idle, a task wakes up, the server stops
* a task wakes up, the server sets itself to idle and stops right away
Address both cases by clearing the server idle flag whenever a fair task
wakes up and accounting also for pending tasks in the definition of idle.
Fixes: f5a538c07d ("sched/deadline: Fix dl_server stop condition")
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260113085159.114226-3-gmonaco@redhat.com
A fix for the dl_server 'requires' idle_cpu() usage, which made me
note that it and available_idle_cpu() are extern function calls.
And while idle_cpu() is used outside of kernel/sched/,
available_idle_cpu() is not.
This makes it hard to make idle_cpu() an inline helper, so provide
idle_rq() and implement idle_cpu() and available_idle_cpu() using
that.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
The access rule for local_cpu_mask_dl requires it to be called on the
local CPU with preemption disabled. However, dl_add_task_root_domain()
currently violates this rule.
Without preemption disabled, the following race can occur:
1. ThreadA calls dl_add_task_root_domain() on CPU 0
2. Gets pointer to CPU 0's local_cpu_mask_dl
3. ThreadA is preempted and migrated to CPU 1
4. ThreadA continues using CPU 0's local_cpu_mask_dl
5. Meanwhile, the scheduler on CPU 0 calls find_later_rq() which also
uses local_cpu_mask_dl (with preemption properly disabled)
6. Both contexts now corrupt the same per-CPU buffer concurrently
Fix this by moving the local_cpu_mask_dl access to the preemption
disabled section.
Closes: https://lore.kernel.org/lkml/aSBjm3mN_uIy64nz@jlelli-thinkpadt14gen4.remote.csb
Fixes: 318e18ed22 ("sched/deadline: Walk up cpuset hierarchy to decide root domain when hot-unplug")
Reported-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Pingfan Liu <piliu@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://patch.msgid.link/20251125032630.8746-3-piliu@redhat.com
The comments above dl_get_task_effective_cpus() and
dl_add_task_root_domain() already explain how to fetch a valid
root domain and protect against races. There's no need to repeat
this inside dl_add_task_root_domain(). Remove the redundant comment
to keep the code clean.
No functional change.
Signed-off-by: Pingfan Liu <piliu@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://patch.msgid.link/20251125032630.8746-2-piliu@redhat.com
Paravirt clock related functions are available in multiple archs.
In order to share the common parts, move the common static keys
to kernel/sched/ and remove them from the arch specific files.
Make a common paravirt_steal_clock() implementation available in
kernel/sched/cputime.c, guarding it with a new config option
CONFIG_HAVE_PV_STEAL_CLOCK_GEN, which can be selected by an arch
in case it wants to use that common variant.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260105110520.21356-7-jgross@suse.com
All architectures supporting CONFIG_PARAVIRT share the same contents
of asm/paravirt_api_clock.h:
#include <asm/paravirt.h>
So remove all incarnations of asm/paravirt_api_clock.h and remove the
only place where it is included, as there asm/paravirt.h is included
anyway.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com> # powerpc, scheduler bits
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260105110520.21356-6-jgross@suse.com
In a vain attempt to consolidate the email zoo switch everything to the
kernel.org account.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
sched_mm_cid_after_execve() is called in bprm_execve()'s cleanup path even
when exec_binprm() fails. For the init task's first execve(), this causes a
problem:
1. current->mm is NULL (kernel threads don't have an mm)
2. sched_mm_cid_before_execve() exits early because mm is NULL
3. exec_binprm() fails (e.g., ENOENT for missing script interpreter)
4. sched_mm_cid_after_execve() is called with mm still NULL
5. sched_mm_cid_fork() is called unconditionally, triggering WARN_ON
This is easily reproduced by booting with an init that is a shell script
(#!/bin/sh) where the interpreter doesn't exist in the initramfs.
Fix this by checking if t->mm is NULL before calling sched_mm_cid_fork(),
matching the behavior of sched_mm_cid_before_execve() which already
handles this case via sched_mm_cid_exit()'s early return.
Fixes: b0c3d51b54 ("sched/mmcid: Provide precomputed maximal value")
Signed-off-by: Cong Wang <cwang@multikernel.io>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://patch.msgid.link/20251223215113.639686-1-xiyou.wangcong@gmail.com
The introduction of PREEMPT_LAZY was for multiple reasons:
- PREEMPT_RT suffered from over-scheduling, hurting performance compared to
!PREEMPT_RT.
- the introduction of (more) features that rely on preemption; like
folio_zero_user() which can do large memset() without preemption checks.
(Xen already had a horrible hack to deal with long running hypercalls)
- the endless and uncontrolled sprinkling of cond_resched() -- mostly cargo
cult or in response to poor to replicate workloads.
By moving to a model that is fundamentally preemptable these things become
managable and avoid needing to introduce more horrible hacks.
Since this is a requirement; limit PREEMPT_NONE to architectures that do not
support preemption at all. Further limit PREEMPT_VOLUNTARY to those
architectures that do not yet have PREEMPT_LAZY support (with the eventual goal
to make this the empty set and completely remove voluntary preemption and
cond_resched() -- notably VOLUNTARY is already limited to !ARCH_NO_PREEMPT.)
This leaves up-to-date architectures (arm64, loongarch, powerpc, riscv, s390,
x86) with only two preemption models: full and lazy.
While Lazy has been the recommended setting for a while, not all distributions
have managed to make the switch yet. Force things along. Keep the patch minimal
in case of hard to address regressions that might pop up.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Link: https://patch.msgid.link/20251219101502.GB1132199@noisy.programming.kicks-ass.net
This colocates some hot fields in "struct rq" to be on the same cache line
as others that are often accessed at the same time or in similar ways.
Using data from a Google-internal fleet-scale profiler, I found three
distinct groups of hot fields in struct rq:
- (1) The runqueue lock: __lock.
- (2) Those accessed from hot code in pick_next_task_fair():
nr_running, nr_numa_running, nr_preferred_running,
ttwu_pending, cpu_capacity, curr, idle.
- (3) Those accessed from some other hot codepaths, e.g.
update_curr(), update_rq_clock(), and scheduler_tick():
clock_task, clock_pelt, clock, lost_idle_time,
clock_update_flags, clock_pelt_idle, clock_idle.
The cycles spent on accessing these different groups of fields broke down
roughly as follows:
- 50% on group (1) (the runqueue lock, always read-write)
- 39% on group (2) (load:store ratio around 38:1)
- 8% on group (3) (load:store ratio around 5:1)
- 3% on all the other fields
Most of the fields in group (3) are already in a cache line grouping; this
patch just adds "clock" and "clock_update_flags" to that group. The fields
in group (2) are scattered across several cache lines; the main effect of
this patch is to group them together, on a single line at the beginning of
the structure. A few other less performance-critical fields (nr_switches,
numa_migrate_on, has_blocked_load, nohz_csd, last_blocked_load_update_tick)
were also reordered to reduce holes in the data structure.
Since the runqueue lock is acquired from so many different contexts, and is
basically always accessed using an atomic operation, putting it on either
of the cache lines for groups (2) or (3) would slow down accesses to those
fields dramatically, since those groups are read-mostly accesses.
To test this, I wrote a focused load test that would put load on the
pick_next_task_fair() path. A parent process would fork many child
processes, and each child would nanosleep() for 1 msec many times in a
loop. The load test was monitored with "perf", and I looked at the amount
of cycles that were spent with sched_balance_rq() on the stack. The test
was reliably spending ~5% of all of its cycles there. I ran it 100 times
on a pair of 2-socket Intel Haswell machines (72 vCPUs per machine) - one
running the tip of sched/core, the other running this change - using 360
child processes and 8192 1-msec sleeps per child. The mean cycle count
dropped from 5.14B to 4.91B, or a *4.6% decrease* in relevant scheduler
cycles.
Given that this change reduces cache misses in a very hot kernel codepath,
there's likely to be additional application performance improvement due to
reduced cache conflicts from kernel data structures.
On a Power11 system with 128-byte cache lines, my test showed a ~5%
decrease in relevant scheduler cycles, along with a slight increase in user
time - both positive indicators. This data comes from
https://lore.kernel.org/lkml/affdc6b1-9980-44d1-89db-d90730c1e384@linux.ibm.com/
This is the case even though the additional "____cacheline_aligned" that
puts the runqueue lock on the next cache line adds an additional 64 bytes
of padding on those machines. This patch does not change the size of
"struct rq" on machines with 64-byte cache lines.
I also ran "hackbench" to try to test this change, but it didn't show
conclusive results. Looking at a CPU cycle profile of the hackbench run,
it was spending 95% of its cycles inside __alloc_skb(), __kfree_skb(), or
kmem_cache_free() - almost all of which was spent updating memcg counters
or contending on the list_lock in kmem_cache_node. And it spent less than
0.5% of its cycles inside either schedule() or try_to_wake_up(). So it's
not surprising that it didn't show useful results here.
The "__no_randomize_layout" was added to reflect the fact that performance
of code that references this data structure is unusually sensitive to
placement of its members.
Signed-off-by: Blake Jones <blakejones@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Reviewed-by: Josh Don <joshdon@google.com>
Tested-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Link: https://patch.msgid.link/20251202023743.1524247-1-blakejones@google.com
In the group_has_spare case, the function creates a temporary cpumask
to just calculate weight of (p->cpus_ptr & sched_group_span(local)).
We've got a dedicated helper for it.
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: Fernand Sieber <sieberf@amazon.com>
Link: https://patch.msgid.link/20251207034247.402926-1-yury.norov@gmail.com
Use for_each_cpu_and() and drop some housekeeping code.
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: Phil Auld <pauld@redhat.com>
Link: https://patch.msgid.link/20251207033037.399608-1-yury.norov@gmail.com
cpumask_empty() call is O(N) and useless because the previous
cpumask_and() returns false for empty 'cpus'. Drop it.
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://patch.msgid.link/20251207040543.407695-1-yury.norov@gmail.com
This demonstrates a larger conversion to use Clang's context
analysis. The benefit is additional static checking of locking rules,
along with better documentation.
Notably, kernel/sched contains sufficiently complex synchronization
patterns, and application to core.c & fair.c demonstrates that the
latest Clang version has become powerful enough to start applying this
to more complex subsystems (with some modest annotations and changes).
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251219154418.3592607-37-elver@google.com
Now that KF_TRUSTED_ARGS is the default for all kfuncs, remove the
explicit KF_TRUSTED_ARGS flag from all kfunc definitions and remove the
flag itself.
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20260102180038.2708325-3-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
llist_add() returns true only when adding to an empty list, which indicates
that no IRQ work is currently queued or running. Therefore, we only need to
call irq_work_queue() when llist_add() returns true, to avoid unnecessarily
re-queueing IRQ work that is already pending or executing.
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
For the PREEMPT_RT kernels, the scx_bypass_lb_timerfn() running in the
preemptible per-CPU ktimer kthread context, this means that the following
scenarios will occur(for x86 platform):
cpu1 cpu2
ktimer kthread:
->scx_bypass_lb_timerfn
->bypass_lb_node
->for_each_cpu(cpu, resched_mask)
migration/1: by preempt by migration/2:
multi_cpu_stop() multi_cpu_stop()
->take_cpu_down()
->__cpu_disable()
->set cpu1 offline
->rq1 = cpu_rq(cpu1)
->resched_curr(rq1)
->smp_send_reschedule(cpu1)
->native_smp_send_reschedule(cpu1)
->if(unlikely(cpu_is_offline(cpu))) {
WARN(1, "sched: Unexpected
reschedule of offline CPU#%d!\n", cpu);
return;
}
This commit therefore use the resched_cpu() to replace resched_curr()
in the bypass_lb_node() to avoid send-ipi to offline CPUs.
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit update balance_scx() in the comments to balance_one().
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Commit 47efe2ddcc ("sched/core: Add assertions to QUEUE_CLASS") added an
assert to sched_change_end() verifying that a class demotion would result in a
reschedule.
As it turns out; rt_mutex_setprio() does not force a resched on class
demontion. Furthermore, this is only relevant to running tasks.
Change the warning into a reschedule and make sure to only do so for running
tasks.
Fixes: 47efe2ddcc ("sched/core: Add assertions to QUEUE_CLASS")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251216141725.GW3707837@noisy.programming.kicks-ass.net
Change sched_class::wakeup_preempt() to also get called for
cross-class wakeups, specifically those where the woken task
is of a higher class than the previous highest class.
In order to do this, track the current highest class of the runqueue
in rq::next_class and have wakeup_preempt() track this upwards for
each new wakeup. Additionally have schedule() re-set the value on
pick.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251127154725.901391274@infradead.org
Smatch reported:
kernel/sched/ext.c:5332 scx_alloc_and_add_sched() warn: passing zero to 'ERR_PTR'
In scx_alloc_and_add_sched(), the alloc_percpu() failure path jumps to
err_free_gdsqs without initializing @ret. That can lead to returning
ERR_PTR(0), which violates the ERR_PTR() convention and confuses
callers.
Set @ret to -ENOMEM before jumping to the error path when
alloc_percpu() fails.
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/r/202512141601.yAXDAeA9-lkp@intel.com/
Reported-by: Dan Carpenter <error27@gmail.com>
Fixes: c201ea1578 ("sched_ext: Move event_stats_cpu into scx_sched")
Signed-off-by: Liang Jie <liangjie@lixiang.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
The kick_idle variable is no longer used, this commit therefore remove
it and also remove associated code in the do_pick_task_scx().
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
There's three layers of logic in the scheduler that
deal with 'has_blocked' (load) handling of the NOHZ code:
(1) nohz.has_blocked,
(2) rq->has_blocked_load, deal with NOHZ idle balancing,
(3) and cfs_rq_has_blocked(), which is part of the layer
that is passing the SMP load-balancing signal to the
NOHZ layers.
The 'has_blocked' and 'has_blocked_load' names are used
in a mixed fashion, sometimes within the same function.
Standardize on 'has_blocked_load' to make it all easy
to read and easy to grep.
No change in functionality.
Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/aS6yvxyc3JfMxxQW@gmail.com
We have to be careful with vruntime comparisons and subtraction,
due to the possibility of wrapping, so we have macros like:
#define vruntime_gt(field, lse, rse) ({ (s64)((lse)->field - (rse)->field) > 0; })
Which is used like this:
if (vruntime_gt(min_vruntime, se, rse))
se->min_vruntime = rse->min_vruntime;
Replace this with an easier to read pattern that uses the regular
arithmetics operators:
if (vruntime_cmp(se->min_vruntime, ">", rse->min_vruntime))
se->min_vruntime = rse->min_vruntime;
Also replace vruntime subtractions with vruntime_op():
- delta = (s64)(sea->vruntime - seb->vruntime) +
- (s64)(cfs_rqb->zero_vruntime_fi - cfs_rqa->zero_vruntime_fi);
+ delta = vruntime_op(sea->vruntime, "-", seb->vruntime) +
+ vruntime_op(cfs_rqb->zero_vruntime_fi, "-", cfs_rqa->zero_vruntime_fi);
In the vruntime_cmp() and vruntime_op() macros use Use __builtin_strcmp(),
because of __HAVE_ARCH_STRCMP might turn off the compiler optimizations
we rely on here to catch usage bugs.
No change in functionality.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The ::avg_vruntime field is a misnomer: it says it's an
'average vruntime', but in reality it's the momentary sum
of the weighted vruntimes of all queued tasks, which is
at least a division away from being an average.
This is clear from comments about the math of fair scheduling:
* \Sum (v_i - v0) * w_i := cfs_rq->avg_vruntime
This confusion is increased by the cfs_avg_vruntime() function,
which does perform the division and returns a true average.
The sum of all weighted vruntimes should be named thusly,
so rename the field to ::sum_w_vruntime. (As arguably
::sum_weighted_vruntime would be a bit of a mouthful.)
Understanding the scheduler is hard enough already, without
extra layers of obfuscated naming. ;-)
Also rename related helper functions:
sum_vruntime_add() => sum_w_vruntime_add()
sum_vruntime_sub() => sum_w_vruntime_sub()
sum_vruntime_update() => sum_w_vruntime_update()
With the notable exception of cfs_avg_vruntime(), which
was named accurately.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251201064647.1851919-7-mingo@kernel.org
The ::avg_load field is a long-standing misnomer: it says it's an
'average load', but in reality it's the momentary sum of the load
of all currently runnable tasks. We'd have to also perform a
division by nr_running (or use time-decay) to arrive at any sort
of average value.
This is clear from comments about the math of fair scheduling:
* \Sum w_i := cfs_rq->avg_load
The sum of all weights is ... the sum of all weights, not
the average of all weights.
To make it doubly confusing, there's also an ::avg_load
in the load-balancing struct sg_lb_stats, which *is* a
true average.
The second part of the field's name is a minor misnomer
as well: it says 'load', and it is indeed a load_weight
structure as it shares code with the load-balancer - but
it's only in an SMP load-balancing context where
load = weight, in the fair scheduling context the primary
purpose is the weighting of different nice levels.
So rename the field to ::sum_weight instead, which makes
the terminology of the EEVDF math match up with our
implementation of it:
* \Sum w_i := cfs_rq->sum_weight
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251201064647.1851919-6-mingo@kernel.org
Join two identical #ifdef blocks:
#ifdef CONFIG_FAIR_GROUP_SCHED
...
#endif
#ifdef CONFIG_FAIR_GROUP_SCHED
...
#endif
Also mark nested #ifdef blocks in the usual fashion, to make
it more apparent where in a nested hierarchy of #ifdefs we
are at a glance.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20251201064647.1851919-2-mingo@kernel.org
Add some checks to the sched_change pattern to validate assumptions
around changing classes.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251127154725.771691954@infradead.org
The task_tick_fair() function does:
- update the hierarchical runtimes
- drive NUMA-balancing
- update load-balance statistics
- drive force-idle preemption
All but the very first can be limited to the periodic tick. Let hrtick
only update accounting and drive preemption, not load-balancing and
other bits.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20250918080205.563385766@infradead.org
With fair switched to rcu_dereference_all() validation, having IRQ or
preemption disabled is sufficient, remove the rcu_read_lock()
clutter.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251127154725.647502625@infradead.org
With the {rcu,sched,bh} RCU flavours being unified, it doesn't really
make sense to check for just the rcu one. Switch to the _all family of
verification which includes all 3 of the listed flavours.
Notably, this will enable us to remove some superfluous
rcu_read_lock() regions when we know they are inside preempt/IRQ
disabled regions.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Remove check from the name for being surplus to requirements.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
While poking at this code recently I noted we do a pointless
unlock+lock cycle in sched_balance_newidle(). We drop the rq->lock (so
we can balance) but then instantly grab the same rq->lock again in
sched_balance_update_blocked_averages().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251127154725.532469061@infradead.org
Nine (and a half) instances of the same pattern is just silly, fold the lot.
Notably, the half instance in enqueue_load_avg() is right after setting
cfs_rq->avg.load_sum to cfs_rq->avg.load_avg * get_pelt_divider(&cfs_rq->avg).
Since get_pelt_divisor() >= PELT_MIN_DIVIDER, this ends up being a no-op
change.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://patch.msgid.link/20251127154725.413564507@infradead.org
move_local_task_to_local_dsq() is used when moving a task from a non-local
DSQ to a local DSQ on the same CPU. It directly manipulates the local DSQ
without going through dispatch_enqueue() and was missing the post-enqueue
handling that triggers preemption when SCX_ENQ_PREEMPT is set or the idle
task is running.
The function is used by move_task_between_dsqs() which backs
scx_bpf_dsq_move() and may be called while the CPU is busy.
Add local_dsq_post_enq() call to move_local_task_to_local_dsq(). As the
dispatch path doesn't need post-enqueue handling, add SCX_RQ_IN_BALANCE
early exit to keep consume_dispatch_q() behavior unchanged and avoid
triggering unnecessary resched when scx_bpf_dsq_move() is used from the
dispatch path.
Fixes: 4c30f5ce4f ("sched_ext: Implement scx_bpf_dispatch[_vtime]_from_dsq()")
Cc: stable@vger.kernel.org # v6.12+
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Factor out local_dsq_post_enq() which performs post-enqueue handling for
local DSQs - triggering resched_curr() if SCX_ENQ_PREEMPT is specified or if
the current CPU is idle. No functional change.
This will be used by the next patch to fix move_local_task_to_local_dsq().
Cc: stable@vger.kernel.org # v6.12+
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_enable() calls scx_bypass(true) to initialize in bypass mode and then
scx_bypass(false) on success to exit. If scx_enable() fails during task
initialization - e.g. scx_cgroup_init() or scx_init_task() returns an error -
it jumps to err_disable while bypass is still active. scx_disable_workfn()
then calls scx_bypass(true/false) for its own bypass, leaving the bypass depth
at 1 instead of 0. This causes the system to remain permanently in bypass mode
after a failed scx_enable().
Failures after task initialization is complete - e.g. scx_tryset_enable_state()
at the end - already call scx_bypass(false) before reaching the error path and
are not affected. This only affects a subset of failure modes.
Fix it by tracking whether scx_enable() called scx_bypass(true) in a bool and
having scx_disable_workfn() call an extra scx_bypass(false) to clear it. This
is a temporary measure as the bypass depth will be moved into the sched
instance, which will make this tracking unnecessary.
Fixes: 8c2090c504 ("sched_ext: Initialize in bypass mode")
Cc: stable@vger.kernel.org # v6.12+
Reported-by: Chris Mason <clm@meta.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/stable/286e6f7787a81239e1ce2989b52391ce%40kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Early when trying to get sched_ext and proxy-exe working together,
I kept tripping over NULL ptr in put_prev_task_scx() on the line:
if (sched_class_above(&ext_sched_class, next->sched_class)) {
Which was due to put_prev_task() passes a NULL next, calling:
prev->sched_class->put_prev_task(rq, prev, NULL);
put_prev_task_scx() already guards for a NULL next in the
switch_class case, but doesn't seem to have a guard for
sched_class_above() check.
I can't say I understand why this doesn't trip usually without
proxy-exec. And in newer kernels there are way fewer
put_prev_task(), and I can't easily reproduce the issue now
even with proxy-exec.
But we still have one put_prev_task() call left in core.c that
seems like it could trip this, so I wanted to send this out for
consideration.
tj: put_prev_task() can be called with NULL @next; however, when @p is
queued, that doesn't happen, so this condition shouldn't currently be
triggerable. The connection isn't straightforward or necessarily reliable,
so add the NULL check even if it can't currently be triggered.
Link: http://lkml.kernel.org/r/20251206022218.1541878-1-jstultz@google.com
Signed-off-by: John Stultz <jstultz@google.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
- Fix psi_dequeue() for Proxy Execution
- Fix hrtick() vs. scheduling context bug
- Fix unfairness caused by stalled tg_load_avg_contrib when the last task migrates out
- Fix whitespace noise in headers
- Remove a preempt-disable section in rt_mutex_setprio()
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-urgent-2025-12-06' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler fixes from Ingo Molnar:
"Miscellaneous scheduler fixes/cleanups:
- Fix psi_dequeue() for Proxy Execution
- Fix hrtick() vs. scheduling context bug
- Fix unfairness caused by stalled tg_load_avg_contrib when the last
task migrates out
- Fix whitespace noise in headers
- Remove a preempt-disable section in rt_mutex_setprio()"
* tag 'sched-urgent-2025-12-06' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/core: Fix psi_dequeue() for Proxy Execution
sched/fair: Fix unfairness caused by stalled tg_load_avg_contrib when the last task migrates out
sched/rt: Remove a preempt-disable section in rt_mutex_setprio()
sched/hrtick: Fix hrtick() vs. scheduling context
sched/headers: Remove whitespace noise from kernel/sched/sched.h
Currently, if the sleep flag is set, psi_dequeue() doesn't
change any of the psi_flags.
This is because psi_task_switch() will clear TSK_ONCPU as well
as other potential flags (TSK_RUNNING), and the assumption is
that a voluntary sleep always consists of a task being dequeued
followed shortly there after with a psi_sched_switch() call.
Proxy Execution changes this expectation, as mutex-blocked tasks
that would normally sleep stay on the runqueue. But in the case
where the mutex-owning task goes to sleep, or the owner is on a
remote cpu, we will then deactivate the blocked task shortly
after.
In that situation, the mutex-blocked task will have had its
TSK_ONCPU cleared when it was switched off the cpu, but it will
stay TSK_RUNNING. Then if we later dequeue it (as currently done
if we hit a case find_proxy_task() can't yet handle, such as the
case of the owner being on another rq or a sleeping owner)
psi_dequeue() won't change any state (leaving it TSK_RUNNING),
as it incorrectly expects a psi_task_switch() call to
immediately follow.
Later on when the task get woken/re-enqueued, and psi_flags are
set for TSK_RUNNING, we hit an error as the task is already
TSK_RUNNING:
psi: inconsistent task state! task=188:kworker/28:0 cpu=28 psi_flags=4 clear=0 set=4
To resolve this, extend the logic in psi_dequeue() so that
if the sleep flag is set, we also check if psi_flags have
TSK_ONCPU set (meaning the psi_task_switch is imminent) before
we do the shortcut return.
If TSK_ONCPU is not set, that means we've already switched away,
and this psi_dequeue call needs to clear the flags.
Fixes: be41bde4c3 ("sched: Add an initial sketch of the find_proxy_task() function")
Reported-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Haiyue Wang <haiyuewa@163.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://patch.msgid.link/20251205012721.756394-1-jstultz@google.com
Closes: https://lore.kernel.org/lkml/20251117185550.365156-1-kprateek.nayak@amd.com/
When a task is migrated out, there is a probability that the tg->load_avg
value will become abnormal. The reason is as follows:
1. Due to the 1ms update period limitation in update_tg_load_avg(), there
is a possibility that the reduced load_avg is not updated to tg->load_avg
when a task migrates out.
2. Even though __update_blocked_fair() traverses the leaf_cfs_rq_list and
calls update_tg_load_avg() for cfs_rqs that are not fully decayed, the key
function cfs_rq_is_decayed() does not check whether
cfs->tg_load_avg_contrib is null. Consequently, in some cases,
__update_blocked_fair() removes cfs_rqs whose avg.load_avg has not been
updated to tg->load_avg.
Add a check of cfs_rq->tg_load_avg_contrib in cfs_rq_is_decayed(),
which fixes the case (2.) mentioned above.
Fixes: 1528c661c2 ("sched/fair: Ratelimit update to tg->load_avg")
Signed-off-by: xupengbo <xupengbo@oppo.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Aaron Lu <ziqianlu@bytedance.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: Aaron Lu <ziqianlu@bytedance.com>
Link: https://patch.msgid.link/20250827022208.14487-1-xupengbo@oppo.com
rt_mutex_setprio() has only one caller: rt_mutex_adjust_prio(). It
expects that task_struct::pi_lock and rt_mutex_base::wait_lock are held.
Both locks are raw_spinlock_t and are acquired with disabled interrupts.
Nevertheless rt_mutex_setprio() disables preemption while invoking
__balance_callbacks() and raw_spin_rq_unlock(). Even if one of the
balance callbacks unlocks the rq then it must not enable interrupts
because rt_mutex_base::wait_lock is still locked.
Therefore interrupts should remain disabled and disabling preemption is
not needed.
Commit 4c9a4bc89a ("sched: Allow balance callbacks for check_class_changed()")
adds a preempt-disable section to rt_mutex_setprio() and
__sched_setscheduler(). In __sched_setscheduler() the preemption is
disabled before rq is unlocked and interrupts enabled but I don't see
why it makes a difference in rt_mutex_setprio().
Remove the preempt_disable() section from rt_mutex_setprio().
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251127155529.t_sTatE4@linutronix.de
