From 7c2e8bbd87db661122e92d71a394dd7bb3ada4d3 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 3 Dec 2019 17:01:05 +0100 Subject: [PATCH] sched: Spare resched IPI when prio changes on a single fair task The runqueue of a fair task being remotely reniced is going to get a resched IPI in order to reassess which task should be the current running on the CPU. However that evaluation is useless if the fair task is running alone, in which case we can spare that IPI, preventing nohz_full CPUs from being disturbed. Reported-by: Peter Zijlstra Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: Ingo Molnar Link: https://lkml.kernel.org/r/20191203160106.18806-2-frederic@kernel.org --- kernel/sched/fair.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 08a233e97a019..846f50bd0c0bb 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10322,6 +10322,9 @@ prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio) if (!task_on_rq_queued(p)) return; + if (rq->cfs.nr_running == 1) + return; + /* * Reschedule if we are currently running on this runqueue and * our priority decreased, or if we are not currently running on -- 2.30.2