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sched: Disable TTWU_QUEUE on RT

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The queued remote wakeup mechanism has turned out to be suboptimal for RT
enabled kernels. The maximum latencies go up by a factor of > 5x in certain
scenarious.

This is caused by either long wake lists or by a large number of TTWU IPIs
which are processed back to back.

Disable it for RT.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210928122411.482262764@linutronix.de
This commit is contained in:
Thomas Gleixner 2021-09-28 14:24:27 +02:00 committed by Peter Zijlstra
parent 691925f3dd
commit 539fbb5be0
1 changed files with 5 additions and 0 deletions
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5
kernel/sched/features.h
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@ -46,11 +46,16 @@ SCHED_FEAT(DOUBLE_TICK, false)
*/
SCHED_FEAT(NONTASK_CAPACITY, true)
#ifdef CONFIG_PREEMPT_RT
SCHED_FEAT(TTWU_QUEUE, false)
#else
/*
* Queue remote wakeups on the target CPU and process them
* using the scheduler IPI. Reduces rq->lock contention/bounces.
*/
SCHED_FEAT(TTWU_QUEUE, true)
#endif
/*
* When doing wakeups, attempt to limit superfluous scans of the LLC domain.