linux-kernel - Re: [PATCH 2/2] sched/fair: Delete useless condition in tg_unthrottle

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Date:   Fri, 8 Apr 2022 09:16:58 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Benjamin Segall <bsegall@...gle.com>
Cc:     Chengming Zhou <zhouchengming@...edance.com>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, mgorman@...e.de,
        bristot@...hat.com, linux-kernel@...r.kernel.org,
        duanxiongchun@...edance.com, songmuchun@...edance.com
Subject: Re: [PATCH 2/2] sched/fair: Delete useless condition in tg_unthrottle_up()

On Thu, 7 Apr 2022 at 23:00, Benjamin Segall <bsegall@...gle.com> wrote:
>
> Chengming Zhou <zhouchengming@...edance.com> writes:
>
> > Fully decayed cfs_rq is impossible to have queued entities,
> > the first condition "!cfs_rq_is_decayed(cfs_rq)" is enough
> > to cover.
>
> In particular, cfs_rq->load.weight is part of cfs_rq_is_decayed.

Testing cfs_rq->load.weight is the key point because nothing prevent
to add a task with null load

Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>

>
> Reviewed-by: Ben Segall <bsegall@...gle.com>
>
> >
> > Signed-off-by: Chengming Zhou <zhouchengming@...edance.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 e6fa5d1141b4..17c13c38b1c2 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -4850,7 +4850,7 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
> >                                            cfs_rq->throttled_clock_task;
> >
> >               /* Add cfs_rq with load or one or more already running entities to the list */
> > -             if (!cfs_rq_is_decayed(cfs_rq) || cfs_rq->nr_running)
> > +             if (!cfs_rq_is_decayed(cfs_rq))
> >                       list_add_leaf_cfs_rq(cfs_rq);
> >       }