Heiko Carstens says:
===================
This is supposed to improve s390 idle time accounting, and brings it
back to the state it was before arch_cpu_idle_time() was removed from
s390 [3].
In result all cpu time accounting is done by the s390 architecture backend
again, instead of having a mix of architecure specific and common code
accounting (common code: idle, s390 architecture: everything else).
===================
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
The former s390 specific arch_cpu_idle_time() implementation was
removed, since its implementation was racy and reported idle time
could go backwards [1].
However this removal was not necessary, since independently of the s390
architecture specific races there exists the iowait counter update race,
which can also lead to reported idle time going backwards [2].
With Frederic Weisbecker's recent cpu idle time accounting refactoring
kernel_cpustat got a sequence counter. Use this to implement s390 specific
variants of kcpustat_field_idle() and kcpustat_field_iowait(). This is
logically a revert of [1] and moves cpu idle time accounting back into s390
architecture code, which is also more precise than the dyntick idle time
accounting by nohz/scheduler.
For comparing cross cpu time stamps it is necessary to use the stcke
instead of the stckf instruction in irq entry path. Furthermore this
open-codes a sequence lock in assembler and C code, which is required to
update the irq entry time stamp to the per cpu idle_data structure in a
race free manner.
[1] commit be76ea6144 ("s390/idle: remove arch_cpu_idle_time() and corresponding code")
[2] commit ead70b7523 ("timers/nohz: Add a comment about broken iowait counter update race")
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
SMP load-balancing updates:
- A large series to introduce infrastructure for cache-aware load
balancing, with the goal of co-locating tasks that share data
within the same Last Level Cache (LLC) domain. By improving cache
locality, the scheduler can reduce cache bouncing and cache misses,
ultimately improving data access efficiency.
Implemented by Chen Yu and Tim Chen, based on early prototype work
by Peter Zijlstra, with fixes by Jianyong Wu, Peter Zijlstra and
Shrikanth Hegde.
- A series to simplify CONFIG_SCHED_SMT ifdef usage (Shrikanth Hegde)
Fair scheduler updates:
- A series to improve SD_ASYM_CPUCAPACITY scheduling by introducing
SMT awareness (Andrea Righi, K Prateek Nayak)
- A series to optimize cfs_rq and sched_entity allocation for
better data locality (Zecheng Li)
- A preparatory series to change fair/cgroup scheduling to a single
runqueue, without the final change (Peter Zijlstra)
- Auto-manage ext/fair dl_server bandwidth (Andrea Righi)
- Fix cpu_util runnable_avg arithmetic (Hongyan Xia)
- Optimize update_tg_load_avg()'s rate-limiting code
(Rik van Riel)
- Allow account_cfs_rq_runtime() to throttle current hierarchy
(K Prateek Nayak)
- Update util_est after updating util_avg during dequeue, to fix
the util signal update logic, which reduces signal noise
(Vincent Guittot)
Scheduler topology updates:
- Allow multiple domains to claim sched_domain_shared (K Prateek Nayak)
- Add parameter to split LLC (Peter Zijlstra)
Core scheduler updates:
- Use trace_call__<tp>() to save a static branch (Gabriele Monaco)
Scheduler statistics updates:
- Drop now-stale mul_u64_u64_div_u64() cputime over-approximation guard
(Nicolas Pitre)
Deadline scheduler updates:
- Reject debugfs dl_server writes for offline CPUs (Andrea Righi)
- Fix replenishment logic for non-deferred servers
(Yuri Andriaccio)
RT scheduling updates:
- Turn RT_PUSH_IPI default off for non PREEMPT_RT (Steven Rostedt)
- Update default bandwidth for real-time tasks to 1.0
(Yuri Andriaccio)
Proxy scheduling updates:
- A series to implement Optimized Donor Migration for Proxy Execution
(John Stultz, Peter Zijlstra)
- Various proxy scheduling cleanups and fixes
(Peter Zijlstra, K Prateek Nayak)
Misc fixes, improvements and cleanups by Aaron Lu, Andrea Righi,
Zenghui Yu, Chen Yu, Guanyou.Chen, John Stultz, Shrikanth Hegde,
Peter Zijlstra, Liang Luo and Yiyang Chen.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-core-2026-06-14' of gitolite.kernel.org:pub/scm/linux/kernel/git/tip/tip
Pull scheduler updates from Ingo Molnar:
"SMP load-balancing updates:
- A large series to introduce infrastructure for cache-aware load
balancing, with the goal of co-locating tasks that share data
within the same Last Level Cache (LLC) domain. By improving cache
locality, the scheduler can reduce cache bouncing and cache misses,
ultimately improving data access efficiency.
Implemented by Chen Yu and Tim Chen, based on early prototype work
by Peter Zijlstra, with fixes by Jianyong Wu, Peter Zijlstra and
Shrikanth Hegde.
- A series to simplify CONFIG_SCHED_SMT ifdef usage (Shrikanth Hegde)
Fair scheduler updates:
- A series to improve SD_ASYM_CPUCAPACITY scheduling by introducing
SMT awareness (Andrea Righi, K Prateek Nayak)
- A series to optimize cfs_rq and sched_entity allocation for better
data locality (Zecheng Li)
- A preparatory series to change fair/cgroup scheduling to a single
runqueue, without the final change (Peter Zijlstra)
- Auto-manage ext/fair dl_server bandwidth (Andrea Righi)
- Fix cpu_util runnable_avg arithmetic (Hongyan Xia)
- Optimize update_tg_load_avg()'s rate-limiting code (Rik van Riel)
- Allow account_cfs_rq_runtime() to throttle current hierarchy
(K Prateek Nayak)
- Update util_est after updating util_avg during dequeue, to fix the
util signal update logic, which reduces signal noise (Vincent
Guittot)
Scheduler topology updates:
- Allow multiple domains to claim sched_domain_shared (K Prateek
Nayak)
- Add parameter to split LLC (Peter Zijlstra)
Core scheduler updates:
- Use trace_call__<tp>() to save a static branch (Gabriele Monaco)
Scheduler statistics updates:
- Drop now-stale mul_u64_u64_div_u64() cputime over-approximation
guard (Nicolas Pitre)
Deadline scheduler updates:
- Reject debugfs dl_server writes for offline CPUs (Andrea Righi)
- Fix replenishment logic for non-deferred servers (Yuri Andriaccio)
RT scheduling updates:
- Turn RT_PUSH_IPI default off for non PREEMPT_RT (Steven Rostedt)
- Update default bandwidth for real-time tasks to 1.0 (Yuri
Andriaccio)
Proxy scheduling updates:
- A series to implement Optimized Donor Migration for Proxy Execution
(John Stultz, Peter Zijlstra)
- Various proxy scheduling cleanups and fixes (Peter Zijlstra,
K Prateek Nayak)
Misc fixes, improvements and cleanups by Aaron Lu, Andrea Righi,
Zenghui Yu, Chen Yu, Guanyou.Chen, John Stultz, Shrikanth Hegde,
Peter Zijlstra, Liang Luo and Yiyang Chen"
* tag 'sched-core-2026-06-14' of gitolite.kernel.org:pub/scm/linux/kernel/git/tip/tip: (91 commits)
sched/fair: Fix newidle vs core-sched
sched/deadline: Use task_on_rq_migrating() helper
sched/core: Combine separate 'else' and 'if' statements
sched/fair: Fix cpu_util runnable_avg arithmetic
sched/fair: Unify cfs_rq throttling via account_cfs_rq_runtime()
sched/fair: Move the throttled tasks to a local list in tg_unthrottle_up()
sched/fair: Call update_curr() before unthrottling the hierarchy
sched/fair: Use throttled_csd_list for local unthrottle
sched/fair: Convert cfs bandwidth throttling to use guards
sched/fair: Allocate cfs_tg_state with percpu allocator
sched/fair: Remove task_group->se pointer array
sched/fair: Co-locate cfs_rq and sched_entity in cfs_tg_state
sched: restore timer_slack_ns when resetting RT policy on fork
MAINTAINERS: Fix spelling mistake in Peter's name
sched: Simplify ttwu_runnable()
sched/proxy: Remove superfluous clear_task_blocked_in()
sched/proxy: Remove PROXY_WAKING
sched/proxy: Switch proxy to use p->is_blocked
sched/proxy: Only return migrate when needed
sched: Be more strict about p->is_blocked
...
The dyntick-idle steal time is currently accounted when the tick restarts
but the stolen idle time is not subtracted from the idle time that was
already accounted. This is to avoid observing the idle time going backward
as the dyntick-idle cputime accessors can't reliably know in advance the
stolen idle time.
In order to maintain a forward progressing idle cputime while subtracting
idle steal time from it, keep track of the previously accounted idle stolen
time and substract it from _later_ idle cputime accounting.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-16-frederic@kernel.org
The dyntick-idle cputime accounting always assumes that interrupt time
accounting is enabled and consequently stops elapsing the idle time during
dyntick-idle interrupts.
This doesn't mix up well with disabled interrupt time accounting because
then idle interrupts become a cputime blind-spot. Also this feature is
disabled on most configurations and the overhead of pausing dyntick-idle
accounting while in idle interrupts could then be avoided.
Fix the situation with conditionally pausing dyntick-idle accounting during
idle interrupts only iff either native vtime (which does interrupt time
accounting) or generic interrupt time accounting are enabled.
Also make sure that the accumulated interrupt time is not accidentally
substracted from later accounting.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-15-frederic@kernel.org
The last reason why get_cpu_idle/iowait_time_us() may return -1 now is if
the config doesn't support nohz.
The ad-hoc replacement solution by cpufreq is to compute jiffies minus the
whole busy cputime. Although the intention should provide a coherent low
resolution estimation of the idle and iowait time, the implementation is
buggy because jiffies don't start at 0.
Just provide instead a real get_cpu_[idle|iowait]_time_us() offcase.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-14-frederic@kernel.org
Fetching the idle cputime is available through a variety of accessors all
over the place depending on the different accounting flavours and needs:
- idle vtime generic accounting can be accessed by kcpustat_field(),
kcpustat_cpu_fetch(), get_idle/iowait_time() and
get_cpu_idle/iowait_time_us()
- dynticks-idle accounting can only be accessed by get_idle/iowait_time()
or get_cpu_idle/iowait_time_us()
- CONFIG_NO_HZ_COMMON=n idle accounting can be accessed by kcpustat_field()
kcpustat_cpu_fetch(), or get_idle/iowait_time() but not by
get_cpu_idle/iowait_time_us()
Moreover get_idle/iowait_time() relies on get_cpu_idle/iowait_time_us()
with a non-sensical conversion to microseconds and back to nanoseconds on
the way.
Start consolidating the APIs with removing get_idle/iowait_time() and make
kcpustat_field() and kcpustat_cpu_fetch() work for all cases.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-13-frederic@kernel.org
Although the dynticks-idle cputime accounting is necessarily tied to the
tick subsystem, the actual related accounting code has no business residing
there and should be part of the scheduler cputime code.
Move away the relevant pieces and state machine to where they belong.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-10-frederic@kernel.org
The non-vtime dynticks-idle cputime accounting is a big mess that
accumulates within two concurrent statistics, each having their own
shortcomings:
* The accounting for online CPUs which is based on the delta between
tick_nohz_start_idle() and tick_nohz_stop_idle().
Pros:
- Works when the tick is off
- Has nsecs granularity
Cons:
- Account idle steal time but doesn't substract it from idle
cputime.
- Assumes CONFIG_IRQ_TIME_ACCOUNTING by not accounting IRQs but
the IRQ time is simply ignored when
CONFIG_IRQ_TIME_ACCOUNTING=n
- The windows between 1) idle task scheduling and the first call
to tick_nohz_start_idle() and 2) idle task between the last
tick_nohz_stop_idle() and the rest of the idle time are
blindspots wrt. cputime accounting (though mostly insignificant
amount)
- Relies on private fields outside of kernel stats, with specific
accessors.
* The accounting for offline CPUs which is based on ticks and the
jiffies delta during which the tick was stopped.
Pros:
- Handles steal time correctly
- Handle CONFIG_IRQ_TIME_ACCOUNTING=y and
CONFIG_IRQ_TIME_ACCOUNTING=n correctly.
- Handles the whole idle task
- Accounts directly to kernel stats, without midlayer accumulator.
Cons:
- Doesn't elapse when the tick is off, which doesn't make it
suitable for online CPUs.
- Has TICK_NSEC granularity (jiffies)
- Needs to track the dyntick-idle ticks that were accounted and
substract them from the total jiffies time spent while the tick
was stopped. This is an ugly workaround.
Having two different accounting for a single context is not the only
problem: since those accountings are of different natures, it is
possible to observe the global idle time going backward after a CPU goes
offline.
Clean up the situation with introducing a hybrid approach that stays
coherent and works for both online and offline CPUs:
* Tick based or native vtime accounting operate before the idle loop
is entered and resume once the idle loop prepares to exit.
* When the idle loop starts, switch to dynticks-idle accounting as is
done currently, except that the statistics accumulate directly to the
relevant kernel stat fields.
* Private dyntick cputime accounting fields are removed.
* Works on both online and offline case.
Further improvement will include:
* Only switch to dynticks-idle cputime accounting when the tick actually
goes in dynticks mode.
* Handle CONFIG_IRQ_TIME_ACCOUNTING=n correctly such that the
dynticks-idle accounting still elapses while on IRQs.
* Correctly substract idle steal cputime from idle time
Reported-by: Xin Zhao <jackzxcui1989@163.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-8-frederic@kernel.org
Currently whether generic vtime is running or not, the idle cputime is
fetched from the nohz accounting.
However generic vtime already does its own idle cputime accounting. Only
the kernel stat accessors are not plugged to support it.
Read the idle generic vtime cputime when it's running, this will allow to
later more clearly split nohz and vtime cputime accounting.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-5-frederic@kernel.org
The first parameter to kcpustat_field() is a pointer to the cpu kcpustat to
be fetched from. This parameter is error prone because a copy to a kcpustat
could be passed by accident instead of the original one. Also the kcpustat
structure can already be retrieved with the help of the mandatory CPU
argument.
Remove the needless parameter.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-4-frederic@kernel.org
Commit 77baa5bafc ("sched/cputime: Fix mul_u64_u64_div_u64() precision
for cputime") added a clamp in cputime_adjust():
if (unlikely(stime > rtime))
stime = rtime;
The justification was that mul_u64_u64_div_u64() could over-approximate
on some architectures (notably arm64 and the old 32-bit fallback), so
the mathematically impossible stime > rtime was nevertheless reachable
and would underflow utime = rtime - stime.
That premise no longer holds. Commit b29a62d87c ("mul_u64_u64_div_u64:
make it precise always") replaced the fallback implementation with an
exact 128-bit long division, and the x86_64 inline asm already produced
exact results. The helper now returns the mathematically correct
floor(a*b/d) on every architecture, so stime <= rtime is guaranteed by
stime <= stime + utime and the clamp is dead code.
Remove it along with its stale comment.
Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260514202629.673539-1-nico@fluxnic.net
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
...
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
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
To simplify the code and make it more readable.
While at it, change thread_group_cputime() to use __for_each_thread(sig).
[peterz: update to new interface]
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Due to the weird Makefile setup of sched the various files do not
compile as stand alone units. The new generation of editors are trying
to do just this -- mostly to offer fancy things like completions but
also better syntax highlighting and code navigation.
Specifically, I've been playing around with neovim and clangd.
Setting up clangd on the kernel source is a giant pain in the arse
(this really should be improved), but once you do manage, you run into
dumb stuff like the above.
Fix up the scheduler files to at least pretend to work.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20250523164348.GN39944@noisy.programming.kicks-ass.net
The sched_clock_irqtime was defined as a static key in:
8722903cbb ("sched: Define sched_clock_irqtime as static key")
However, this change introduces a 'sleeping in atomic context' warning:
arch/x86/kernel/tsc.c:1214 mark_tsc_unstable()
warn: sleeping in atomic context
As analyzed by Dan, the affected code path is as follows:
vcpu_load() <- disables preempt
-> kvm_arch_vcpu_load()
-> mark_tsc_unstable() <- sleeps
virt/kvm/kvm_main.c
166 void vcpu_load(struct kvm_vcpu *vcpu)
167 {
168 int cpu = get_cpu();
^^^^^^^^^^
This get_cpu() disables preemption.
169
170 __this_cpu_write(kvm_running_vcpu, vcpu);
171 preempt_notifier_register(&vcpu->preempt_notifier);
172 kvm_arch_vcpu_load(vcpu, cpu);
173 put_cpu();
174 }
arch/x86/kvm/x86.c
4979 if (unlikely(vcpu->cpu != cpu) || kvm_check_tsc_unstable()) {
4980 s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 :
4981 rdtsc() - vcpu->arch.last_host_tsc;
4982 if (tsc_delta < 0)
4983 mark_tsc_unstable("KVM discovered backwards TSC");
arch/x86/kernel/tsc.c
1206 void mark_tsc_unstable(char *reason)
1207 {
1208 if (tsc_unstable)
1209 return;
1210
1211 tsc_unstable = 1;
1212 if (using_native_sched_clock())
1213 clear_sched_clock_stable();
--> 1214 disable_sched_clock_irqtime();
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
kernel/jump_label.c
245 void static_key_disable(struct static_key *key)
246 {
247 cpus_read_lock();
^^^^^^^^^^^^^^^^
This lock has a might_sleep() in it which triggers the static checker
warning.
248 static_key_disable_cpuslocked(key);
249 cpus_read_unlock();
250 }
Let revert this change for now as {disable,enable}_sched_clock_irqtime
are used in many places, as pointed out by Sean, including the following:
The code path in clocksource_watchdog():
clocksource_watchdog()
|
-> spin_lock(&watchdog_lock);
|
-> __clocksource_unstable()
|
-> clocksource.mark_unstable() == tsc_cs_mark_unstable()
|
-> disable_sched_clock_irqtime()
And the code path in sched_clock_register():
/* Cannot register a sched_clock with interrupts on */
local_irq_save(flags);
...
/* Enable IRQ time accounting if we have a fast enough sched_clock() */
if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
enable_sched_clock_irqtime();
local_irq_restore(flags);
[ lkp@intel.com: reported a build error in the prev version ]
[ mingo: cherry-picked it over into sched/urgent ]
Closes: https://lore.kernel.org/kvm/37a79ba3-9ce0-479c-a5b0-2bd75d573ed3@stanley.mountain/
Fixes: 8722903cbb ("sched: Define sched_clock_irqtime as static key")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Debugged-by: Dan Carpenter <dan.carpenter@linaro.org>
Debugged-by: Sean Christopherson <seanjc@google.com>
Debugged-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20250205032438.14668-1-laoar.shao@gmail.com
Since CPU time accounting is a performance-critical path, let's define
sched_clock_irqtime as a static key to minimize potential overhead.
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Michal Koutný <mkoutny@suse.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20250103022409.2544-2-laoar.shao@gmail.com
In extreme test scenarios:
the 14th field utime in /proc/xx/stat is greater than sum_exec_runtime,
utime = 18446744073709518790 ns, rtime = 135989749728000 ns
In cputime_adjust() process, stime is greater than rtime due to
mul_u64_u64_div_u64() precision problem.
before call mul_u64_u64_div_u64(),
stime = 175136586720000, rtime = 135989749728000, utime = 1416780000.
after call mul_u64_u64_div_u64(),
stime = 135989949653530
unsigned reversion occurs because rtime is less than stime.
utime = rtime - stime = 135989749728000 - 135989949653530
= -199925530
= (u64)18446744073709518790
Trigger condition:
1). User task run in kernel mode most of time
2). ARM64 architecture
3). TICK_CPU_ACCOUNTING=y
CONFIG_VIRT_CPU_ACCOUNTING_NATIVE is not set
Fix mul_u64_u64_div_u64() conversion precision by reset stime to rtime
Fixes: 3dc167ba57 ("sched/cputime: Improve cputime_adjust()")
Signed-off-by: Zheng Zucheng <zhengzucheng@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20240726023235.217771-1-zhengzucheng@huawei.com
The generic vtime_task_switch() implementation gets built only
if __ARCH_HAS_VTIME_TASK_SWITCH is not defined, but requires an
architecture to implement arch_vtime_task_switch() callback at
the same time, which is confusing.
Further, arch_vtime_task_switch() is implemented for 32-bit PowerPC
architecture only and vtime_task_switch() generic variant is rather
superfluous.
Simplify the whole vtime_task_switch() wiring by moving the existing
generic implementation to PowerPC.
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/2cb6e3caada93623f6d4f78ad938ac6cd0e2fda8.1712760275.git.agordeev@linux.ibm.com
The archs that use cputime_to_nsecs() internally provide their own
definition and don't need the fallback. cputime_to_usecs() unused except
in this fallback, and is not defined anywhere.
This removes the final remnant of the cputime_t code from the kernel.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Link: https://lore.kernel.org/r/20221220070705.2958959-1-npiggin@gmail.com
4feee7d126 previously added per-task forced idle accounting. This patch
extends this to also include cgroups.
rstat is used for cgroup accounting, except for the root, which uses
kcpustat in order to bypass the need for doing an rstat flush when
reading root stats.
Only cgroup v2 is supported. Similar to the task accounting, the cgroup
accounting requires that schedstats is enabled.
Signed-off-by: Josh Don <joshdon@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lkml.kernel.org/r/20220629211426.3329954-1-joshdon@google.com
Similarly to kernel/sched/build_utility.c, collect all 'scheduling policy' related
source code files into kernel/sched/build_policy.c:
kernel/sched/idle.c
kernel/sched/rt.c
kernel/sched/cpudeadline.c
kernel/sched/pelt.c
kernel/sched/cputime.c
kernel/sched/deadline.c
With the exception of fair.c, which we continue to build as a separate file
for build efficiency and parallelism reasons.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Peter Zijlstra <peterz@infradead.org>
"Mostly minor things this time; some highlights:
- core-sched: Add 'Forced Idle' accounting; this allows to track how
much CPU time is 'lost' due to core scheduling constraints.
- psi: Fix for MEM_FULL; a task running reclaim would be counted as a
runnable task and prevent MEM_FULL from being reported.
- cpuacct: Long standing fixes for some cgroup accounting issues.
- rt: Bandwidth timer could, under unusual circumstances, be failed to
armed, leading to indefinite throttling."
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Merge tag 'sched_core_for_v5.17_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler updates from Borislav Petkov:
"Mostly minor things this time; some highlights:
- core-sched: Add 'Forced Idle' accounting; this allows to track how
much CPU time is 'lost' due to core scheduling constraints.
- psi: Fix for MEM_FULL; a task running reclaim would be counted as a
runnable task and prevent MEM_FULL from being reported.
- cpuacct: Long standing fixes for some cgroup accounting issues.
- rt: Bandwidth timer could, under unusual circumstances, be failed
to armed, leading to indefinite throttling."
[ Description above by Peter Zijlstra ]
* tag 'sched_core_for_v5.17_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/fair: Replace CFS internal cpu_util() with cpu_util_cfs()
sched/fair: Cleanup task_util and capacity type
sched/rt: Try to restart rt period timer when rt runtime exceeded
sched/fair: Document the slow path and fast path in select_task_rq_fair
sched/fair: Fix per-CPU kthread and wakee stacking for asym CPU capacity
sched/fair: Fix detection of per-CPU kthreads waking a task
sched/cpuacct: Make user/system times in cpuacct.stat more precise
sched/cpuacct: Fix user/system in shown cpuacct.usage*
cpuacct: Convert BUG_ON() to WARN_ON_ONCE()
cputime, cpuacct: Include guest time in user time in cpuacct.stat
psi: Fix PSI_MEM_FULL state when tasks are in memstall and doing reclaim
sched/core: Forced idle accounting
psi: Add a missing SPDX license header
psi: Remove repeated verbose comment
getrusage(RUSAGE_THREAD) with nohz_full may return shorter utime/stime
than the actual time.
task_cputime_adjusted() snapshots utime and stime and then adjust their
sum to match the scheduler maintained cputime.sum_exec_runtime.
Unfortunately in nohz_full, sum_exec_runtime is only updated once per
second in the worst case, causing a discrepancy against utime and stime
that can be updated anytime by the reader using vtime.
To fix this situation, perform an update of cputime.sum_exec_runtime
when the cputime snapshot reports the task as actually running while
the tick is disabled. The related overhead is then contained within the
relevant situations.
Reported-by: Hasegawa Hitomi <hasegawa-hitomi@fujitsu.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Hasegawa Hitomi <hasegawa-hitomi@fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Acked-by: Phil Auld <pauld@redhat.com>
Link: https://lore.kernel.org/r/20211026141055.57358-3-frederic@kernel.org
cpuacct.stat in no-root cgroups shows user time without guest time
included int it. This doesn't match with user time shown in root
cpuacct.stat and /proc/<pid>/stat. This also affects cgroup2's cpu.stat
in the same way.
Make account_guest_time() to add user time to cgroup's cpustat to
fix this.
Fixes: ef12fefabf ("cpuacct: add per-cgroup utime/stime statistics")
Signed-off-by: Andrey Ryabinin <arbn@yandex-team.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20211115164607.23784-1-arbn@yandex-team.com
- Clean up SCHED_DEBUG: move the decades old mess of sysctl, procfs and debugfs interfaces
to a unified debugfs interface.
- Signals: Allow caching one sigqueue object per task, to improve performance & latencies.
- Improve newidle_balance() irq-off latencies on systems with a large number of CPU cgroups.
- Improve energy-aware scheduling
- Improve the PELT metrics for certain workloads
- Reintroduce select_idle_smt() to improve load-balancing locality - but without the previous
regressions
- Add 'scheduler latency debugging': warn after long periods of pending need_resched. This
is an opt-in feature that requires the enabling of the LATENCY_WARN scheduler feature,
or the use of the resched_latency_warn_ms=xx boot parameter.
- CPU hotplug fixes for HP-rollback, and for the 'fail' interface. Fix remaining
balance_push() vs. hotplug holes/races
- PSI fixes, plus allow /proc/pressure/ files to be written by CAP_SYS_RESOURCE tasks as well
- Fix/improve various load-balancing corner cases vs. capacity margins
- Fix sched topology on systems with NUMA diameter of 3 or above
- Fix PF_KTHREAD vs to_kthread() race
- Minor rseq optimizations
- Misc cleanups, optimizations, fixes and smaller updates
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-core-2021-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler updates from Ingo Molnar:
- Clean up SCHED_DEBUG: move the decades old mess of sysctl, procfs and
debugfs interfaces to a unified debugfs interface.
- Signals: Allow caching one sigqueue object per task, to improve
performance & latencies.
- Improve newidle_balance() irq-off latencies on systems with a large
number of CPU cgroups.
- Improve energy-aware scheduling
- Improve the PELT metrics for certain workloads
- Reintroduce select_idle_smt() to improve load-balancing locality -
but without the previous regressions
- Add 'scheduler latency debugging': warn after long periods of pending
need_resched. This is an opt-in feature that requires the enabling of
the LATENCY_WARN scheduler feature, or the use of the
resched_latency_warn_ms=xx boot parameter.
- CPU hotplug fixes for HP-rollback, and for the 'fail' interface. Fix
remaining balance_push() vs. hotplug holes/races
- PSI fixes, plus allow /proc/pressure/ files to be written by
CAP_SYS_RESOURCE tasks as well
- Fix/improve various load-balancing corner cases vs. capacity margins
- Fix sched topology on systems with NUMA diameter of 3 or above
- Fix PF_KTHREAD vs to_kthread() race
- Minor rseq optimizations
- Misc cleanups, optimizations, fixes and smaller updates
* tag 'sched-core-2021-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (61 commits)
cpumask/hotplug: Fix cpu_dying() state tracking
kthread: Fix PF_KTHREAD vs to_kthread() race
sched/debug: Fix cgroup_path[] serialization
sched,psi: Handle potential task count underflow bugs more gracefully
sched: Warn on long periods of pending need_resched
sched/fair: Move update_nohz_stats() to the CONFIG_NO_HZ_COMMON block to simplify the code & fix an unused function warning
sched/debug: Rename the sched_debug parameter to sched_verbose
sched,fair: Alternative sched_slice()
sched: Move /proc/sched_debug to debugfs
sched,debug: Convert sysctl sched_domains to debugfs
debugfs: Implement debugfs_create_str()
sched,preempt: Move preempt_dynamic to debug.c
sched: Move SCHED_DEBUG sysctl to debugfs
sched: Don't make LATENCYTOP select SCHED_DEBUG
sched: Remove sched_schedstats sysctl out from under SCHED_DEBUG
sched/numa: Allow runtime enabling/disabling of NUMA balance without SCHED_DEBUG
sched: Use cpu_dying() to fix balance_push vs hotplug-rollback
cpumask: Introduce DYING mask
cpumask: Make cpu_{online,possible,present,active}() inline
rseq: Optimise rseq_get_rseq_cs() and clear_rseq_cs()
...
Fix ~42 single-word typos in scheduler code comments.
We have accumulated a few fun ones over the years. :-)
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: linux-kernel@vger.kernel.org
vtime_account_irq and irqtime_account_irq() base checks on preempt_count()
which fails on RT because preempt_count() does not contain the softirq
accounting which is seperate on RT.
These checks do not need the full preempt count as they only operate on the
hard and softirq sections.
Use irq_count() instead which provides the correct value on both RT and non
RT kernels. The compiler is clever enough to fold the masking for !RT:
99b: 65 8b 05 00 00 00 00 mov %gs:0x0(%rip),%eax
- 9a2: 25 ff ff ff 7f and $0x7fffffff,%eax
+ 9a2: 25 00 ff ff 00 and $0xffff00,%eax
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210309085727.153926793@linutronix.de
IRQ time entry is currently accounted before HARDIRQ_OFFSET or
SOFTIRQ_OFFSET are incremented. This is convenient to decide to which
index the cputime to account is dispatched.
Unfortunately it prevents tick_irq_enter() from being called under
HARDIRQ_OFFSET because tick_irq_enter() has to be called before the IRQ
entry accounting due to the necessary clock catch up. As a result we
don't benefit from appropriate lockdep coverage on tick_irq_enter().
To prepare for fixing this, move the IRQ entry cputime accounting after
the preempt offset is incremented. This requires the cputime dispatch
code to handle the extra offset.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20201202115732.27827-5-frederic@kernel.org
The 3 architectures implementing CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
all have their own version of irq time accounting that dispatch the
cputime to the appropriate index: hardirq, softirq, system, idle,
guest... from an all-in-one function.
Instead of having these ad-hoc versions, move the cputime destination
dispatch decision to the core code and leave only the actual per-index
cputime accounting to the architecture.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201202115732.27827-4-frederic@kernel.org
s390 has its own version of IRQ entry accounting because it doesn't
account the idle time the same way the other architectures do. Only
the actual idle sleep time is accounted as idle time, the rest of the
idle task execution is accounted as system time.
Make the generic IRQ entry accounting aware of architectures that have
their own way of accounting idle time and convert s390 to use it.
This prepares s390 to get involved in further consolidations of IRQ
time accounting.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201202115732.27827-3-frederic@kernel.org
account_irq_enter_time() and account_irq_exit_time() are not called
from modules. EXPORT_SYMBOL_GPL() can be safely removed from the IRQ
cputime accounting functions called from there.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201202115732.27827-2-frederic@kernel.org
People report that utime and stime from /proc/<pid>/stat become very
wrong when the numbers are big enough, especially if you watch these
counters incrementally.
Specifically, the current implementation of: stime*rtime/total,
results in a saw-tooth function on top of the desired line, where the
teeth grow in size the larger the values become. IOW, it has a
relative error.
The result is that, when watching incrementally as time progresses
(for large values), we'll see periods of pure stime or utime increase,
irrespective of the actual ratio we're striving for.
Replace scale_stime() with a math64.h helper: mul_u64_u64_div_u64()
that is far more accurate. This also allows architectures to override
the implementation -- for instance they can opt for the old algorithm
if this new one turns out to be too expensive for them.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200519172506.GA317395@hirez.programming.kicks-ass.net
Work around this warning:
kernel/sched/cputime.c: In function ‘kcpustat_field’:
kernel/sched/cputime.c:1007:6: warning: ‘val’ may be used uninitialized in this function [-Wmaybe-uninitialized]
because GCC can't see that val is used only when err is 0.
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200327214334.GF8015@zn.tnic
As the vtime is sampled under loose seqcount protection by kcpustat, the
vtime fields may change as the code flows. Where logic dictates a field
has a static value, use a READ_ONCE.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Fixes: 74722bb223 ("sched/vtime: Bring up complete kcpustat accessor")
Link: https://lkml.kernel.org/r/20200123180849.28486-1-frederic@kernel.org
Every time we call irqtime_account_process_tick() is in a interrupt,
Every caller will get and assign a parameter rq = this_rq(), This is
unnecessary and increase the code size a little bit. Move the rq getting
action to irqtime_account_process_tick internally is better.
base with this patch
cputime.o 578792 bytes 577888 bytes
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/1577959674-255537-1-git-send-email-alex.shi@linux.alibaba.com
Many callsites want to fetch the values of system, user, user_nice, guest
or guest_nice kcpustat fields altogether or at least a pair of these.
In that case calling kcpustat_field() for each requested field brings
unecessary overhead when we could fetch all of them in a row.
So provide kcpustat_cpu_fetch() that fetches the whole kcpustat array
in a vtime safe way under the same RCU and seqcount block.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191121024430.19938-3-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Provide support for user, nice, guest and guest_nice fields through
kcpustat_field().
Whether we account the delta to a nice or not nice field is decided on
top of the nice value snapshot taken at the time we call kcpustat_field().
If the nice value of the task has been changed since the last vtime
update, we may have inacurrate distribution of the nice VS unnice
cputime.
However this is considered as a minor issue compared to the proper fix
that would involve interrupting the target on nice updates, which is
undesired on nohz_full CPUs.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191121024430.19938-2-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Kcpustat is not correctly supported on nohz_full CPUs. The tick doesn't
fire and the cputime therefore doesn't move forward. The issue has shown
up after the vanishing of the remaining 1Hz which has made the stall
visible.
We are solving that with checking the task running on a CPU through RCU
and reading its vtime delta that we add to the raw kcpustat values.
We make sure that we fetch a coherent raw-kcpustat/vtime-delta couple
sequence while checking that the CPU referred by the target vtime is the
correct one, under the locked vtime seqcount.
Only CPUTIME_SYSTEM is handled here as a start because it's the trivial
case. User and guest time will require more preparation work to
correctly handle niceness.
Reported-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <wanpengli@tencent.com>
Link: https://lkml.kernel.org/r/20191025020303.19342-1-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Standardize the naming on top of the vtime_accounting_enabled_*() base.
Also make it clear we are checking the vtime state of the
*current* CPU with this function. We'll need to add an API to check that
state on remote CPUs as well, so we must disambiguate the naming.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rjw@rjwysocki.net>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191016025700.31277-9-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Record guest as a VTIME state instead of guessing it from VTIME_SYS and
PF_VCPU. This is going to simplify the cputime read side especially as
its state machine is going to further expand in order to fully support
kcpustat on nohz_full.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rjw@rjwysocki.net>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191016025700.31277-4-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Record idle as a VTIME state instead of guessing it from VTIME_SYS and
is_idle_task(). This is going to simplify the cputime read side
especially as its state machine is going to further expand in order to
fully support kcpustat on nohz_full.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rjw@rjwysocki.net>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191016025700.31277-3-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
In order to compute the kcpustat delta on a nohz CPU, we'll need to
fetch the task running on that target. Checking that its vtime
state snapshot actually refers to the relevant target involves recording
that CPU under the seqcount locked on task switch.
This is a step toward making kcpustat moving forward on full nohz CPUs.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rjw@rjwysocki.net>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191016025700.31277-2-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
On context switch we are locking the vtime seqcount of the scheduling-out
task twice:
* On vtime_task_switch_common(), when we flush the pending vtime through
vtime_account_system()
* On arch_vtime_task_switch() to reset the vtime state.
This is pointless as these actions can be performed without the need
to unlock/lock in the middle. The reason these steps are separated is to
consolidate a very small amount of common code between
CONFIG_VIRT_CPU_ACCOUNTING_GEN and CONFIG_VIRT_CPU_ACCOUNTING_NATIVE.
Performance in this fast path is definitely a priority over artificial
code factorization so split the task switch code between GEN and
NATIVE and mutualize the parts than can run under a single seqcount
locked block.
As a side effect, vtime_account_idle() becomes included in the seqcount
protection. This happens to be a welcome preparation in order to
properly support kcpustat under vtime in the future and fetch
CPUTIME_IDLE without race.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191003161745.28464-3-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
vtime_account_system() decides if we need to account the time to the
system (__vtime_account_system()) or to the guest (vtime_account_guest()).
So this function is a misnomer as we are on a higher level than
"system". All we know when we call that function is that we are
accounting kernel cputime. Whether it belongs to guest or system time
is a lower level detail.
Rename this function to vtime_account_kernel(). This will clarify things
and avoid too many underscored vtime_account_system() versions.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191003161745.28464-2-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
vtime_account_system() assumes that the target task to account cputime
to is always the current task. This is most often true indeed except on
task switch where we call:
vtime_common_task_switch(prev)
vtime_account_system(prev)
Here prev is the scheduling-out task where we account the cputime to. It
doesn't match current that is already the scheduling-in task at this
stage of the context switch.
So we end up checking the wrong task flags to determine if we are
accounting guest or system time to the previous task.
As a result the wrong task is used to check if the target is running in
guest mode. We may then spuriously account or leak either system or
guest time on task switch.
Fix this assumption and also turn vtime_guest_enter/exit() to use the
task passed in parameter as well to avoid future similar issues.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <wanpengli@tencent.com>
Fixes: 2a42eb9594 ("sched/cputime: Accumulate vtime on top of nsec clocksource")
Link: https://lkml.kernel.org/r/20190925214242.21873-1-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
