linux-kernel - Re: [PATCH 1/1] sched/fair:Reduce unnecessary check preempt in the sched tick

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Date:   Wed, 14 Apr 2021 10:10:19 +0800
From:   jun qian <qianjun.kernel@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Benjamin Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] sched/fair:Reduce unnecessary check preempt in the
 sched tick

Peter Zijlstra <peterz@...radead.org> 于2021年4月13日周二 下午10:24写道：
>
> On Tue, Apr 13, 2021 at 09:18:42PM +0800, qianjun.kernel@...il.com wrote:
> > From: jun qian <qianjun.kernel@...il.com>
> >
> > If it has been determined that the current cpu need resched in the
> > early stage of for_each_sched_entity, then there is no need to check
> > preempt in the subsequent se->parent entity_tick.
>
> Right, but does it actually do anything, except increase linecount?
>
> > Signed-off-by: jun qian <qianjun.kernel@...il.com>
> > ---
> >  kernel/sched/fair.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1a68a0536add..c0d135100d54 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -4352,8 +4352,13 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> >  {
> >       unsigned long ideal_runtime, delta_exec;
> >       struct sched_entity *se;
> > +     struct rq *rq = rq_of(cfs_rq);
> >       s64 delta;
> >
> > +     /* If the TIF_NEED_RESCHED has been set, it is no need to check again */
> > +     if (test_tsk_need_resched(rq->curr))
> > +             return;
> > +
> >       ideal_runtime = sched_slice(cfs_rq, curr);
> >       delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
> >       if (delta_exec > ideal_runtime) {
>
> Also, I think that's placed wrong; this way we can mis clear_buddies().

thanks, i will modify it in the next version