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Date:   Wed, 31 Jul 2019 17:30:27 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Rik van Riel <riel@surriel.com>
Cc:     linux-kernel@vger.kernel.org, kernel-team@fb.com, pjt@google.com,
        dietmar.eggemann@arm.com, mingo@redhat.com,
        morten.rasmussen@arm.com, tglx@linutronix.de,
        mgorman@techsingularity.net, vincent.guittot@linaro.org
Subject: Re: [PATCH 09/14] sched,fair: refactor enqueue/dequeue_entity
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On Wed, Jul 31, 2019 at 11:03:01AM -0400, Rik van Riel wrote:

> I think I understand the problem you are pointing out, but if
> update_load_avg() keeps the load average for the runqueue unchanged
> (because that is rate limited to once a jiffy, and has been like that
> for a while), why would calc_group_shares() result in a different
> value than what it returned the last time?
>=20
> What am I overlooking?

I'm thinking you're thinking (3):

           tg->weight * grq->avg.load_avg
  shares =3D ------------------------------
                 tg->load_avg

Where: tg->load_avg ~=3D \Sum grq->avg.load_avg


Which is the straight forward shares calculation, and purely depends on
the load averages (which haven't been changed etc..)

But what we actually do is (6):

                                    tg->weight * grq->avg.load_avg
  shares =3D --------------------------------------------------------------=
-------------
           tg->load_avg - grq->avg.load_avg + max(grq->load.weight, grq->av=
g.load_avg)

And even if tg->load_avg and grq->avg.load_avg haven't changed,
grq->load.weight most certainly has.