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From:   jun qian <qianjun.kernel@gmail.com>
Date:   Wed, 14 Apr 2021 10:10:19 +0800
Message-ID: <CAKc596J1eEqYjYy9dnK6VriGU6GE-7be-6Tq4VA5UUhCp3+ZMQ@mail.gmail.com>
Subject: Re: [PATCH 1/1] sched/fair:Reduce unnecessary check preempt in the
 sched tick
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Benjamin Segall <bsegall@google.com>,
        Mel Gorman <mgorman@suse.de>, linux-kernel@vger.kernel.org
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Peter Zijlstra <peterz@infradead.org> =E4=BA=8E2021=E5=B9=B44=E6=9C=8813=E6=
=97=A5=E5=91=A8=E4=BA=8C =E4=B8=8B=E5=8D=8810:24=E5=86=99=E9=81=93=EF=BC=9A
>
> On Tue, Apr 13, 2021 at 09:18:42PM +0800, qianjun.kernel@gmail.com wrote:
> > From: jun qian <qianjun.kernel@gmail.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@gmail.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 =3D rq_of(cfs_rq);
> >       s64 delta;
> >
> > +     /* If the TIF_NEED_RESCHED has been set, it is no need to check a=
gain */
> > +     if (test_tsk_need_resched(rq->curr))
> > +             return;
> > +
> >       ideal_runtime =3D sched_slice(cfs_rq, curr);
> >       delta_exec =3D curr->sum_exec_runtime - curr->prev_sum_exec_runti=
me;
> >       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