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sched: Add Lazy preemption model

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Change fair to use resched_curr_lazy(), which, when the lazy
preemption model is selected, will set TIF_NEED_RESCHED_LAZY.

This LAZY bit will be promoted to the full NEED_RESCHED bit on tick.
As such, the average delay between setting LAZY and actually
rescheduling will be TICK_NSEC/2.

In short, Lazy preemption will delay preemption for fair class but
will function as Full preemption for all the other classes, most
notably the realtime (RR/FIFO/DEADLINE) classes.

The goal is to bridge the performance gap with Voluntary, such that we
might eventually remove that option entirely.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lkml.kernel.org/r/20241007075055.331243614@infradead.org
This commit is contained in:
Peter Zijlstra
2024-10-04 14:46:58 +02:00
parent 26baa1f1c4
commit 7c70cb94d2
6 changed files with 107 additions and 8 deletions
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8
include/linux/preempt.h
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@@ -486,6 +486,7 @@ DEFINE_LOCK_GUARD_0(migrate, migrate_disable(), migrate_enable())
extern bool preempt_model_none(void);
extern bool preempt_model_voluntary(void);
extern bool preempt_model_full(void);
extern bool preempt_model_lazy(void);
#else
@@ -502,6 +503,11 @@ static inline bool preempt_model_full(void)
return IS_ENABLED(CONFIG_PREEMPT);
}
static inline bool preempt_model_lazy(void)
{
return IS_ENABLED(CONFIG_PREEMPT_LAZY);
}
#endif
static inline bool preempt_model_rt(void)
@@ -519,7 +525,7 @@ static inline bool preempt_model_rt(void)
*/
static inline bool preempt_model_preemptible(void)
{
return preempt_model_full() || preempt_model_rt();
return preempt_model_full() || preempt_model_lazy() || preempt_model_rt();
}
#endif /* __LINUX_PREEMPT_H */