linux-kernel - Re: [PATCH 1/1] sched/fair: Fix unfairness caused by missing load decay

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Date:   Sat, 1 May 2021 16:41:03 +0200
From:   Odin Ugedal <odin@...dal.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Odin Ugedal <odin@...d.al>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] sched/fair: Fix unfairness caused by missing load decay

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