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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Thu, 27 May 2021 16:19:08 +0200
Message-ID: <CAKfTPtAK2fkzhzKA8iFT8cEcCG6Q=8WfLskPYADvTrQ=nF7kDA@mail.gmail.com>
Subject: Re: [PATCH 0/2] schd/fair: fix stalled cfs_rq->tg_load_avg_contrib
To:     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>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Odin Ugedal <odin@uged.al>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@vger.kernel.org>
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Hi Odin,

On Thu, 27 May 2021 at 14:29, Vincent Guittot
<vincent.guittot@linaro.org> wrote:
>
> Odin reported some fairness problem between cgroup because of stalled
> value in cfs_rq->tg_load_avg_contrib:
>
> https://lkml.org/lkml/2021/5/18/566
>
>
> 2 problems generated this situation:
> -1st: After propagating load in the hierarchy, load_sum can be null
>  whereas load_avg isn't so the cfs_rq is removed whereas it still
>  contribute to th tg's load
> -2nd: cfs_rq->tg_load_avg_contrib was not always updated after
>  significant changes like becoming null because cfs_rq had already
>  been updated when propagating a child load.
>

This series fixes the problem triggered by your 1st script on my test
machine. But could you confirm that this patchset also fixes the
problem on yours

Regards,
Vincent

>
> Vincent Guittot (2):
>   sched/fair: keep load_avg and load_sum synced
>   sched/fair: make sure to update tg contrib for blocked load
>
>  kernel/sched/fair.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> --
> 2.17.1
>