The following commit has been merged into the sched/core branch of tip: Commit-ID: 539fbb5be0da56ffa1434b4f56521a0522bd1d61 Gitweb: https://git.kernel.org/tip/539fbb5be0da56ffa1434b4f56521a0522bd1d61 Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> AuthorDate: Tue, 28 Sep 2021 14:24:27 +02:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Tue, 05 Oct 2021 15:52:12 +02:00 sched: Disable TTWU_QUEUE on RT 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@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20210928122411.482262764@xxxxxxxxxxxxx --- kernel/sched/features.h | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/sched/features.h b/kernel/sched/features.h index 7f8dace..1cf435b 100644 --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -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.
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