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sched: dynamic: Remove HAVE_PREEMPT_DYNAMIC_{CALL,KEY}

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PREEMPT_DYNAMIC is now limited to the FULL and LAZY preemption models.
Switching model only changes the behaviour of dynamic_preempt_lazy(),
which uses a static key. There are no other static calls or static keys,
and so there's no need for HAVE_PREEMPT_DYNAMIC_CALL or
HAVE_PREEMPT_DYNAMIC_KEY.

The static key used by dynamic_preempt_lazy() is entirely local to
kernel/sched/core.c, and any architecture which selects
ARCH_HAS_PREEMPT_LAZY implements the necessary support. Remove
PREEMPT_DYNAMIC's dependencies on HAVE_PREEMPT_DYNAMIC_CALL and
HAVE_PREEMPT_DYNAMIC_KEY entirely, leaving the dependency on
ARCH_HAS_PREEMPT_LAZY.

For architectures which previously selected HAVE_PREEMPT_DYNAMIC_KEY,
PREEMPT_DYNAMIC will now be selected by default, matching x86. As the
runtime impact is limited to dynamic_preempt_lazy(), this shouldn't be
as concerning as previously (e.g. where calls to {cond,might}_resched()
stubs could introduce a measurable penalty).

As all of this can work without jump labels, JUMP_LABEL is not selected
explicitly. It is obviously preferable to have JUMP_LABEL enabled, but
this is not functionally necessary.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Tested-by: Mete Durlu <meted@linux.ibm.com>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Tested-by: Jinjie Ruan <ruanjinjie@huawei.com>
Link: https://patch.msgid.link/20260803191731.3244294-6-mark.rutland@arm.com
This commit is contained in:
Mark Rutland 2026-08-03 20:17:30 +01:00 committed by Peter Zijlstra
parent aa4178f638
commit 5b9a28eeed
9 changed files with 2 additions and 60 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
arch/Kconfig
View File

@ -1712,44 +1712,6 @@ config HAVE_STATIC_CALL_INLINE
depends on HAVE_STATIC_CALL
select OBJTOOL
config HAVE_PREEMPT_DYNAMIC
bool
config HAVE_PREEMPT_DYNAMIC_CALL
bool
depends on HAVE_STATIC_CALL
select HAVE_PREEMPT_DYNAMIC
help
An architecture should select this if it can handle the preemption
model being selected at boot time using static calls.
Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a
preemption function will be patched directly.
Where an architecture does not select HAVE_STATIC_CALL_INLINE, any
call to a preemption function will go through a trampoline, and the
trampoline will be patched.
It is strongly advised to support inline static call to avoid any
overhead.
config HAVE_PREEMPT_DYNAMIC_KEY
bool
depends on HAVE_ARCH_JUMP_LABEL
select HAVE_PREEMPT_DYNAMIC
help
An architecture should select this if it can handle the preemption
model being selected at boot time using static keys.
Each preemption function will be given an early return based on a
static key. This should have slightly lower overhead than non-inline
static calls, as this effectively inlines each trampoline into the
start of its callee. This may avoid redundant work, and may
integrate better with CFI schemes.
This will have greater overhead than using inline static calls as
the call to the preemption function cannot be entirely elided.
config ARCH_WANT_LD_ORPHAN_WARN
bool
help

1
arch/arm64/Kconfig
View File

@ -217,7 +217,6 @@ config ARM64
select HAVE_PERF_EVENTS_NMI if ARM64_PSEUDO_NMI
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
select HAVE_PREEMPT_DYNAMIC_KEY
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RELIABLE_STACKTRACE
select HAVE_POSIX_CPU_TIMERS_TASK_WORK

1
arch/loongarch/Kconfig
View File

@ -170,7 +170,6 @@ config LOONGARCH
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
select HAVE_PREEMPT_DYNAMIC_KEY
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RELIABLE_STACKTRACE if UNWINDER_ORC
select HAVE_RETHOOK

1
arch/powerpc/Kconfig
View File

@ -279,7 +279,6 @@ config PPC
select HAVE_PERF_EVENTS_NMI if PPC64
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
select HAVE_PREEMPT_DYNAMIC_KEY
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
select HAVE_RETHOOK if KPROBES
select HAVE_REGS_AND_STACK_ACCESS_API

1
arch/riscv/Kconfig
View File

@ -195,7 +195,6 @@ config RISCV
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
select HAVE_PREEMPT_DYNAMIC_KEY
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RETHOOK
select HAVE_RSEQ

1
arch/s390/Kconfig
View File

@ -246,7 +246,6 @@ config S390
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
select HAVE_PREEMPT_DYNAMIC_KEY
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RELIABLE_STACKTRACE
select HAVE_RETHOOK

1
arch/x86/Kconfig
View File

@ -297,7 +297,6 @@ config X86
select HAVE_STACK_VALIDATION if HAVE_OBJTOOL
select HAVE_STATIC_CALL
select HAVE_STATIC_CALL_INLINE if HAVE_OBJTOOL
select HAVE_PREEMPT_DYNAMIC_CALL
select HAVE_RSEQ
select HAVE_RUST if X86_64
select HAVE_SYSCALL_TRACEPOINTS

8
kernel/Kconfig.preempt
View File

@ -132,11 +132,9 @@ config PREEMPTION
config PREEMPT_DYNAMIC
bool "Preemption behaviour defined on boot"
depends on HAVE_PREEMPT_DYNAMIC
depends on ARCH_HAS_PREEMPT_LAZY
select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY
select PREEMPT_BUILD
default y if HAVE_PREEMPT_DYNAMIC_CALL
default y
help
This option allows to define the preemption model on the kernel
command line parameter and thus override the default preemption
@ -146,9 +144,7 @@ config PREEMPT_DYNAMIC
provide a pre-built kernel binary to reduce the number of kernel
flavors they offer while still offering different usecases.
The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
but if runtime patching is not available for the specific architecture
then the potential overhead should be considered.
The runtime overhead is negligible.
Interesting if you want the same pre-built kernel should be used for
both Server and Desktop workloads.

10
kernel/sched/core.c
View File

@ -7886,16 +7886,6 @@ int sched_dynamic_mode(const char *str)
# define preempt_dynamic_key_enable(f) static_key_enable(&sk_dynamic_##f.key)
# define preempt_dynamic_key_disable(f) static_key_disable(&sk_dynamic_##f.key)
# if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
# define preempt_dynamic_enable(f) static_call_update(f, f##_dynamic_enabled)
# define preempt_dynamic_disable(f) static_call_update(f, f##_dynamic_disabled)
# elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
# define preempt_dynamic_enable(f) preempt_dynamic_key_enable(f)
# define preempt_dynamic_disable(f) preempt_dynamic_key_disable(f)
# else
# error "Unsupported PREEMPT_DYNAMIC mechanism"
# endif
static DEFINE_MUTEX(sched_dynamic_mutex);
static void __sched_dynamic_update(int mode)