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From:   Valentin Schneider <valentin.schneider@arm.com>
To:     Vincent Guittot <vincent.guittot@linaro.org>
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>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sched/fair: improve spreading of utilization
In-reply-to: <CAKfTPtCopLDoUsC+Mt6k99Hdn52pcKkrNYQsYNRW5LdgyMg4Nw@mail.gmail.com>
Date:   Fri, 13 Mar 2020 17:34:09 +0000
Message-ID: <jhjzhcknoq6.mognet@arm.com>
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On Fri, Mar 13 2020, Vincent Guittot wrote:
>> My point is that if we prevent this for migrate_util, it would make
>> sense to prevent it for migrate_task, but it's not straightforward since
>
> hmm but we don't want to prevent this active balance for migrate_task
> because of cases like the one you mentioned above.
>
> we might consider to finally select a CPU with only 1 running task
> with migrate_util if there is no other CPU with more than 1 task. But
> this would complexify the code and I don't think it's possible because
> migrate_util is used to pull some utilizations from an overloaded
> group which must have a CPU with a waiting task to be overloaded.
>

OK, so what we may want in the future is a tighter link between
find_busiest_queue() and voluntary_active_balance(). I don't see a neat
way of doing this right now, I'll ponder over it.

Thanks for keeping up with my rambling.