linux-kernel - Re: [PATCH] sched/fair: avoid vruntime compensation for SCHED

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Message-ID: <CAPJCdBmrLu7-RDrPSeMRNEF0tdFJfRveupqpFFR2AELax2rpWw@mail.gmail.com>
Date:   Thu, 20 Aug 2020 22:15:59 +0800
From:   Jiang Biao <benbjiang@...il.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Jiang Biao <benbjiang@...cent.com>
Subject: Re: [PATCH] sched/fair: avoid vruntime compensation for SCHED_IDLE task

On Thu, 20 Aug 2020 at 20:51, Vincent Guittot
<vincent.guittot@...aro.org> wrote:
>
> On Thu, 20 Aug 2020 at 14:00, Jiang Biao <benbjiang@...il.com> wrote:
> >
> > From: Jiang Biao <benbjiang@...cent.com>
> >
> > Vruntime compensation has been down in place_entity() to
> > boot the waking procedure for fair tasks. There is no need to
>
> s/boot/boost/ ?
Yes. -:)
>
> > do that for SCHED_IDLE task actually.
> >
> > Not compensating vruntime for SCHED_IDLE task could make
> > SCHED_IDLE task more harmless for normal tasks.
> >
> > Signed-off-by: Jiang Biao <benbjiang@...cent.com>
> > ---
> >  kernel/sched/fair.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1a68a0536add..adff77676a0a 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -4115,7 +4115,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
> >                 vruntime += sched_vslice(cfs_rq, se);
> >
> >         /* sleeps up to a single latency don't count. */
> > -       if (!initial) {
> > +       if (!initial && likely(!task_has_idle_policy(task_of(se)))) {
>
> What if se is not a task ?
Is it ok to limit the case to task se, like?
+       if (!initial && likely(!entity_is_task(se) ||
!task_has_idle_policy(task_of(se)))) {

Thx.
Regards,
Jiang
>
> >                 unsigned long thresh = sysctl_sched_latency;
> >
> >                 /*
> > --
> > 2.21.0
> >