linux-kernel - Re: [PATCH 1/2] sched/fair: keep load_avg and load

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Date:   Thu, 27 May 2021 15:37:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Odin Ugedal <odin@...d.al>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched/fair: keep load_avg and load_sum synced

On Thu, May 27, 2021 at 03:18:35PM +0200, Vincent Guittot wrote:
> > -       delta_sum = load_sum - (s64)se_weight(se) * se->avg.load_sum;
> > -       delta_avg = load_avg - se->avg.load_avg;
> > -
> >         se->avg.load_sum = runnable_sum;
> >         se->avg.load_avg = load_avg;
> > -       add_positive(&cfs_rq->avg.load_avg, delta_avg);
> > -       add_positive(&cfs_rq->avg.load_sum, delta_sum);
> > +
> > +       add_positive(&cfs_rq->avg.load_avg, (long)(load_avg - se->avg.load_avg));
> 
> you have to keep:
> delta_avg = load_avg - se->avg.load_avg
> or move se->avg.load_avg = load_avg after
> add_positive(&cfs_rq->avg.load_avg, ..);
> because otherwise (load_avg - se->avg.load_avg) == 0

Duh. /me goes fix.