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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Thu, 27 May 2021 12:49:22 +0200
Message-ID: <CAKfTPtArj_XkgPXRJKZxN0MM2+v=3+RjAVVkmbpB1gBLCuzJvA@mail.gmail.com>
Subject: Re: [PATCH 1/3] sched/fair: Add tg_load_contrib cfs_rq decay checking
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 Thu, 27 May 2021 at 11:46, Odin Ugedal <odin@uged.al> wrote:
>
> Hi,
>
> > I finally got it this morning with your script and I confirm that the
> > problem of load_sum == 0 but load_avg != 0 comes from
> > update_tg_cfs_load(). Then, it seems that we don't call
> > update_tg_load_avg for this cfs_rq in __update_blocked_fair() because
> > of a recent update while propagating child's load changes. At the end
> > we remove the cfs_rq from the list without updating its contribution.
> >
> > I'm going to prepare a patch to fix this
>
> Yeah, that is another way to look at it. Have not verified, but
> wouldn't update_tg_load_avg() in this case
> just remove the diff (load_avg - tg_load_avg_contrib)? Wouldn't we
> still see some tg_load_avg_contrib
> after the cfs_rq is removed from the list then? Eg. in my example
> above, the cfs_rq will be removed from
> the list while tg_load_avg_contrib=2, or am I missing something? That
> was my thought when I looked
> at it last week at least..

1st : ensure that cfs_rq->load_sum is not null if cfs_rq-> load_isn't too
2nd : call update_tg_load_avg() during child update so we will be sure
to update tg_load_avg_contrib before removing the cfs from the list

>
> Thanks
> Odin