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Date: Mon, 23 May 2016 11:58:45 +0100 From: Morten Rasmussen <morten.rasmussen@....com> To: peterz@...radead.org, mingo@...hat.com Cc: dietmar.eggemann@....com, yuyang.du@...el.com, vincent.guittot@...aro.org, mgalbraith@...e.de, linux-kernel@...r.kernel.org, Morten Rasmussen <morten.rasmussen@....com> Subject: [PATCH 03/16] sched/fair: Disregard idle task wakee_flips in wake_wide wake_wide() is based on task wakee_flips of the waker and the wakee to decide whether an affine wakeup is desirable. On lightly loaded systems the waker is frequently the idle task (pid=0) which can accumulate a lot of wakee_flips in that scenario. It makes little sense to prevent affine wakeups on an idle cpu due to the idle task wakee_flips, so it makes more sense to ignore them in wake_wide(). cc: Ingo Molnar <mingo@...hat.com> cc: Peter Zijlstra <peterz@...radead.org> Signed-off-by: Morten Rasmussen <morten.rasmussen@....com> --- kernel/sched/fair.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c49e25a..0fe3020 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5007,6 +5007,10 @@ static int wake_wide(struct task_struct *p) unsigned int slave = p->wakee_flips; int factor = this_cpu_read(sd_llc_size); + /* Don't let the idle task prevent affine wakeups */ + if (is_idle_task(current)) + return 0; + if (master < slave) swap(master, slave); if (slave < factor || master < slave * factor) -- 1.9.1
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