linux-kernel - Re: [RFC PATCH 1/3] sched/fair: Call newidle_balance() from finish_task

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Message-ID: <20200511105800.GB2940@hirez.programming.kicks-ass.net>
Date:   Mon, 11 May 2020 12:58:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Scott Wood <swood@...hat.com>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Rik van Riel <riel@...riel.com>,
        Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
        linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [RFC PATCH 1/3] sched/fair: Call newidle_balance() from
 finish_task_switch()

On Wed, Apr 29, 2020 at 08:31:39PM -0500, Scott Wood wrote:
> > If you were to do a queue_balance_callback() from somewhere in the
> > pick_next_task() machinery, then the balance_callback() at the end of
> > __schedule() would run it, and it'd be gone. How would
> > rt_mutex_setprio() / __sched_setscheduler() be affected?
> 
> The rq lock is dropped between queue_balance_callback() and the
> balance_callback() at the end of __schedule().  What stops
> setprio/setscheduler on another cpu from doing the callback at that
> point?

Hurmm.. fair point, and that might explain some issues I had a while
back. Let me poke a little at that.