Commit 539fbb5b authored Sep 28, 2021 by Thomas Gleixner Committed by Peter Zijlstra Oct 05, 2021

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@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210928122411.482262764@linutronix.de

parent 691925f3

kernel/sched/features.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -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.