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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Mon, 31 May 2021 14:14:02 +0200
Message-ID: <CAKfTPtAwErfdVwdHFULGwbZj5D1axiB-A_AeY49R=aD9p6cezw@mail.gmail.com>
Subject: Re: [PATCH 2/3] sched/fair: Correctly insert cfs_rq's to list on unthrottle
To:     Odin Ugedal <odin@uged.al>
Cc:     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>
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On Sat, 29 May 2021 at 11:34, Odin Ugedal <odin@uged.al> wrote:
>
> Hi,
>
> > normally tg_load_avg_contrib should be null when cfs_rq_is_decayed()
>
> Yeah, I think that is an ok assumption of how it _should_ work (given
> the other patches in flight are merged).
>
> > The reason of this list is to ensure that the load of all cfs_rq are
> > periodically updated  as it is then used to share the runtime between
> > groups so we should keep to use the rule whenever possible.
>
> Yeah, right.
>
> > we probably need to keep (cfs_rq->nr_running >= 1) as we can have case
> > where tg_load_avg_contrib is null but a task is enqueued
>
> Yeah, there is probably a chance of enqueuing a task without any load,
> and then a parent gets throttled.
> So (cfs_rq->tg_load_avg_contrib || cfs_rq->nr_running) is probably the
> way to go if we want to avoid
> a new field. Will resend a patch with that instead.

Thanks

>
> In case the new field is the main issue with the original solution, we
> could also change the on_list int to have three modes like; NO, YES,
> THROTTLED/PAUSED, but that would require a bigger rewrite of the other
> logic, so probably outside the scope of this patch.
>
> Thanks
> Odin