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In-Reply-To: <4ba77def-c7e9-326e-7b5c-cd491b063888@arm.com>
From:   Odin Ugedal <odin@ugedal.com>
Date:   Sat, 1 May 2021 16:41:03 +0200
Message-ID: <CAFpoUr3vMQq8QYajXZsQ6zWQOncO5Q8-2gFWOJLFm-APUznuZA@mail.gmail.com>
Subject: Re: [PATCH 1/1] sched/fair: Fix unfairness caused by missing load decay
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     Vincent Guittot <vincent.guittot@linaro.org>,
        Odin Ugedal <odin@uged.al>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.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>,
        open list <linux-kernel@vger.kernel.org>
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Hi,

> I think what I see on my Juno running the unfairness_missing_load_decay.sh script is
> in sync which what you discussed here:

Thanks for taking a look!

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 794c2cb945f8..7214e6e89820 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10854,6 +10854,8 @@ static void propagate_entity_cfs_rq(struct sched_entity *se)
>                         break;
>
>                 update_load_avg(cfs_rq, se, UPDATE_TG);
> +               if (!cfs_rq_is_decayed(cfs_rq))
> +                       list_add_leaf_cfs_rq(cfs_rq);
>         }
> }

This might however lead to "loss" at /slice/cg-2/sub and
slice/cg-1/sub in this particular case tho, since
propagate_entity_cfs_rq skips one cfs_rq
by taking the parent of the provided se. The loss in that case would
however not be equally big, but will still often contribute to some
unfairness.


Thanks
Odin