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Date:   Tue, 05 Oct 2021 14:12:12 -0000
From:   "tip-bot2 for Josh Don" <>
Cc:     Josh Don <>,
        "Peter Zijlstra (Intel)" <>,
        Vincent Guittot <>,
        Jiang Biao <>,,
Subject: [tip: sched/core] sched: adjust sleeper credit for SCHED_IDLE entities

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

Commit-ID:     2cae3948edd488ebdef4deaf1d1043f92f47e665
Author:        Josh Don <>
AuthorDate:    Thu, 19 Aug 2021 18:04:03 -07:00
Committer:     Peter Zijlstra <>
CommitterDate: Tue, 05 Oct 2021 15:51:39 +02:00

sched: adjust sleeper credit for SCHED_IDLE entities

Give reduced sleeper credit to SCHED_IDLE entities. As a result, woken
SCHED_IDLE entities will take longer to preempt normal entities.

The benefit of this change is to make it less likely that a newly woken
SCHED_IDLE entity will preempt a short-running normal entity before it

We still give a small sleeper credit to SCHED_IDLE entities, so that
idle<->idle competition retains some fairness.

Example: With HZ=1000, spawned four threads affined to one cpu, one of
which was set to SCHED_IDLE. Without this patch, wakeup latency for the
SCHED_IDLE thread was ~1-2ms, with the patch the wakeup latency was

Signed-off-by: Josh Don <>
Signed-off-by: Peter Zijlstra (Intel) <>
Reviewed-by: Vincent Guittot <>
Reviewed-by: Jiang Biao <>
 kernel/sched/fair.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d835061..5457c80 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4230,7 +4230,12 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
 	/* sleeps up to a single latency don't count. */
 	if (!initial) {
-		unsigned long thresh = sysctl_sched_latency;
+		unsigned long thresh;
+		if (se_is_idle(se))
+			thresh = sysctl_sched_min_granularity;
+		else
+			thresh = sysctl_sched_latency;
 		 * Halve their sleep time's effect, to allow

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