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sched: Provide Kconfig support for default dynamic preempt mode

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Currently the boot defined preempt behaviour (aka dynamic preempt)
selects full preemption by default when the "preempt=" boot parameter
is omitted. However distros may rather want to default to either
no preemption or voluntary preemption.

To provide with this flexibility, make dynamic preemption a visible
Kconfig option and adapt the preemption behaviour selected by the user
to either static or dynamic preemption.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210914103134.11309-1-frederic@kernel.org
This commit is contained in:
Frederic Weisbecker 2021-09-14 12:31:34 +02:00 committed by Peter Zijlstra
parent 32ed980c30
commit c597bfddc9
2 changed files with 49 additions and 12 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

32
kernel/Kconfig.preempt
View file

@ -2,10 +2,11 @@
choice
prompt "Preemption Model"
default PREEMPT_NONE
default PREEMPT_NONE_BEHAVIOUR
config PREEMPT_NONE
config PREEMPT_NONE_BEHAVIOUR
bool "No Forced Preemption (Server)"
select PREEMPT_NONE if !PREEMPT_DYNAMIC
help
This is the traditional Linux preemption model, geared towards
throughput. It will still provide good latencies most of the
@ -17,9 +18,10 @@ config PREEMPT_NONE
raw processing power of the kernel, irrespective of scheduling
latencies.
config PREEMPT_VOLUNTARY
config PREEMPT_VOLUNTARY_BEHAVIOUR
bool "Voluntary Kernel Preemption (Desktop)"
depends on !ARCH_NO_PREEMPT
select PREEMPT_VOLUNTARY if !PREEMPT_DYNAMIC
help
This option reduces the latency of the kernel by adding more
"explicit preemption points" to the kernel code. These new
@ -35,12 +37,10 @@ config PREEMPT_VOLUNTARY
Select this if you are building a kernel for a desktop system.
config PREEMPT
config PREEMPT_BEHAVIOUR
bool "Preemptible Kernel (Low-Latency Desktop)"
depends on !ARCH_NO_PREEMPT
select PREEMPTION
select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
select PREEMPT_DYNAMIC if HAVE_PREEMPT_DYNAMIC
select PREEMPT
help
This option reduces the latency of the kernel by making
all kernel code (that is not executing in a critical section)
@ -58,7 +58,7 @@ config PREEMPT
config PREEMPT_RT
bool "Fully Preemptible Kernel (Real-Time)"
depends on EXPERT && ARCH_SUPPORTS_RT
depends on EXPERT && ARCH_SUPPORTS_RT && !PREEMPT_DYNAMIC
select PREEMPTION
help
This option turns the kernel into a real-time kernel by replacing
@ -75,6 +75,17 @@ config PREEMPT_RT
endchoice
config PREEMPT_NONE
bool
config PREEMPT_VOLUNTARY
bool
config PREEMPT
bool
select PREEMPTION
select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
config PREEMPT_COUNT
bool
@ -83,7 +94,10 @@ config PREEMPTION
select PREEMPT_COUNT
config PREEMPT_DYNAMIC
bool
bool "Preemption behaviour defined on boot"
depends on HAVE_PREEMPT_DYNAMIC
select PREEMPT
default y
help
This option allows to define the preemption model on the kernel
command line parameter and thus override the default preemption

29
kernel/sched/core.c
View file

@ -6520,12 +6520,13 @@ EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace);
*/
enum {
preempt_dynamic_none = 0,
preempt_dynamic_undefined = -1,
preempt_dynamic_none,
preempt_dynamic_voluntary,
preempt_dynamic_full,
};
int preempt_dynamic_mode = preempt_dynamic_full;
int preempt_dynamic_mode = preempt_dynamic_undefined;
int sched_dynamic_mode(const char *str)
{
@ -6598,7 +6599,27 @@ static int __init setup_preempt_mode(char *str)
}
__setup("preempt=", setup_preempt_mode);
#endif /* CONFIG_PREEMPT_DYNAMIC */
static void __init preempt_dynamic_init(void)
{
if (preempt_dynamic_mode == preempt_dynamic_undefined) {
if (IS_ENABLED(CONFIG_PREEMPT_NONE_BEHAVIOUR)) {
sched_dynamic_update(preempt_dynamic_none);
} else if (IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY_BEHAVIOUR)) {
sched_dynamic_update(preempt_dynamic_voluntary);
} else {
/* Default static call setting, nothing to do */
WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_BEHAVIOUR));
preempt_dynamic_mode = preempt_dynamic_full;
pr_info("Dynamic Preempt: full\n");
}
}
}
#else /* !CONFIG_PREEMPT_DYNAMIC */
static inline void preempt_dynamic_init(void) { }
#endif /* #ifdef CONFIG_PREEMPT_DYNAMIC */
/*
* This is the entry point to schedule() from kernel preemption
@ -9398,6 +9419,8 @@ void __init sched_init(void)
init_uclamp();
preempt_dynamic_init();
scheduler_running = 1;
}