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sched: Spare resched IPI when prio changes on a single fair task

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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 <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20191203160106.18806-2-frederic@kernel.org
This commit is contained in:
Frederic Weisbecker 2019-12-03 17:01:05 +01:00 committed by Peter Zijlstra
parent 025f50f386
commit 7c2e8bbd87
1 changed files with 3 additions and 0 deletions
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3
kernel/sched/fair.c
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@ -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