From e4edf768c8c8c831d2c058524796c8d61cdccea2 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 28 Sep 2021 14:24:27 +0200 Subject: [PATCH 069/158] 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 Signed-off-by: Sebastian Andrzej Siewior Link: https://lore.kernel.org/r/20210928122411.482262764@linutronix.de --- kernel/sched/features.h | 5 +++++ 1 file changed, 5 insertions(+) Index: linux-5.15.19-rt29/kernel/sched/features.h =================================================================== --- linux-5.15.19-rt29.orig/kernel/sched/features.h +++ linux-5.15.19-rt29/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.