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Date:   Tue, 05 Oct 2021 14:11:57 -0000
From:   "tip-bot2 for Thomas Gleixner" <>
Cc:     Thomas Gleixner <>,
        "Peter Zijlstra (Intel)" <>,,
Subject: [tip: sched/core] sched: Disable TTWU_QUEUE on RT

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     539fbb5be0da56ffa1434b4f56521a0522bd1d61
Author:        Thomas Gleixner <>
AuthorDate:    Tue, 28 Sep 2021 14:24:27 +02:00
Committer:     Peter Zijlstra <>
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

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: Peter Zijlstra (Intel) <>
 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)
  * Queue remote wakeups on the target CPU and process them
  * using the scheduler IPI. Reduces rq->lock contention/bounces.
  * When doing wakeups, attempt to limit superfluous scans of the LLC domain.

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