linux-kernel - Re: [PATCH v6 1/4] sched/fair: Fix attaching task sched avgs twice when switching to fair or changing task group

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Date:	Wed, 15 Jun 2016 08:18:18 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Benjamin Segall <bsegall@...gle.com>,
	Paul Turner <pjt@...gle.com>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH v6 1/4] sched/fair: Fix attaching task sched avgs twice
 when switching to fair or changing task group

On Wed, Jun 15, 2016 at 09:46:53AM +0200, Vincent Guittot wrote:
> I still have concerned with this change of the behavior that  attaches
> the task only when it is enqueued. The load avg of the task will not
> be decayed between the time we move it into its new group until its
> enqueue. With this change, a task's load can stay high whereas it has
> slept for the last couple of seconds.

The task will be updated when it is moved in the detach, so if it stays
high, it is highly expected to be enqueued soon. But if the task is never
enqueued, we don't bother the new gruop cfs_rq.

So this is not perfect, and nothing is perfect, but a simple solution.