linux-kernel - Re: [PATCH 2/3] sched/fair: don't set LBF_ALL

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Date:   Wed, 6 Jan 2021 16:45:39 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.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>
Subject: Re: [PATCH 2/3] sched/fair: don't set LBF_ALL_PINNED unnecessarily

On Wed, 6 Jan 2021 at 16:32, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Jan 06, 2021 at 04:20:55PM +0100, Vincent Guittot wrote:
>
> > This case here is :
> > we have 2 tasks TA and TB on the rq.
> > The waiting one TB can't migrate for a reason other than the pinned case.
> > We decide to start the active migration on the running  TA task but TA
> > is pinned.
> > In this case we are not in the all pinned case.
>
> But then can_migrate_task(TB) should clear ALL_PINNED, no?

Yes but current code sets ALL_PINNED when the active migration failed
because the running task is pinned whatever there is not pinned
waiting tasks that has not been selected