linux-kernel - Re: [PATCH 3/3] sched/fair: reduce cases for active balance

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Message-ID: <X/XhFzKo/Gv+bFsx@hirez.programming.kicks-ass.net>
Date:   Wed, 6 Jan 2021 17:11:03 +0100
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>
Subject: Re: [PATCH 3/3] sched/fair: reduce cases for active balance

On Wed, Jan 06, 2021 at 04:41:04PM +0100, Vincent Guittot wrote:

> Let me try again:
> 
> Active balance is triggered for a number of voluntary cases like
> misfit or pinned tasks cases but also after that a number of load
> balance attempts failed to migrate a task. There is no need to use
> active load balance when the group is overloaded because an overloaded
> state means that there is at least one waiting task. Nevertheless, the
> waiting task is not selected and detached until the threshold becomes
> higher than its load. This threshold increases with the number of
> failed lb (see the condition if ((load >> env->sd->nr_balance_failed)
> > env->imbalance) in detach_tasks()) and the waiting task will end up
> to be selected after a number of attempts.

Ah, makes sense now. Thanks!