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References: <20210604102314.697749-1-odin@uged.al> <YL+dTtsCtZjMeZWn@blackbook>
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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Thu, 10 Jun 2021 08:49:39 +0200
Message-ID: <CAKfTPtBEZZo9fHDxe7viLyZmCe=4NTLLtBFyWM_UuJ1nmqxGvA@mail.gmail.com>
Subject: Re: [PATCH v4] sched/fair: Correctly insert cfs_rq's to list on unthrottle
To:     =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>
Cc:     Odin Ugedal <odin@uged.al>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Giovanni Gherdovich <ggherdovich@suse.cz>
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On Tue, 8 Jun 2021 at 18:39, Michal Koutn=C3=BD <mkoutny@suse.com> wrote:
>
> Hello.
>
> On Fri, Jun 04, 2021 at 12:23:14PM +0200, Odin Ugedal <odin@uged.al> wrot=
e:
>
> > @@ -4719,8 +4738,8 @@ static int tg_unthrottle_up(struct task_group *tg=
, void *data)
> >               cfs_rq->throttled_clock_task_time +=3D rq_clock_task(rq) =
-
> >                                            cfs_rq->throttled_clock_task=
;
> >
> > -             /* Add cfs_rq with already running entity in the list */
> > -             if (cfs_rq->nr_running >=3D 1)
> > +             /* Add cfs_rq with load or one or more already running en=
tities to the list */
> > +             if (!cfs_rq_is_decayed(cfs_rq) || cfs_rq->nr_running)
> >                       list_add_leaf_cfs_rq(cfs_rq);
> >       }
>
> Can there be a decayed cfs_rq with positive nr_running?
> I.e. can the condition be simplified to just the decayed check?

Yes, nothing prevent a task with a null load to be enqueued on a
throttle cfs as an example

>
> (I'm looking at account_entity_enqueue() but I don't know if an entity's
> weight can be zero in some singular cases.)
>
> Thanks,
> Michal