linux-kernel - Re: [PATCH 1/2] sched: make fair sched class can handle the cgroup change by other class

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Message-ID: <20151013090654.GR3604@twins.programming.kicks-ass.net>
Date:	Tue, 13 Oct 2015 11:06:54 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	byungchul.park@....com
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	yuyang.du@...el.com, pjt@...gle.com, efault@....de,
	tglx@...utronix.de
Subject: Re: [PATCH 1/2] sched: make fair sched class can handle the cgroup
 change by other class

On Mon, Oct 05, 2015 at 06:16:23PM +0900, byungchul.park@....com wrote:
> From: Byungchul Park <byungchul.park@....com>
> 
> Original fair sched class can handle the cgroup change occured within its
> class with task_move_group_fair(), but there is no way to know it if the
> change happened outside. This patch makes the fair sched class can handle
> the change of cgroup which happened even at other sched class.
> 
> Additionally, it makes sched_move_task() more flexable so that any other
> sched class can add task_move_group_xx() callback easily in future when
> it is needed.

I don't get the problem... when !fair, set_task_rq() will do what needs
doing.

The only reason we need task_move_group_fair() is the extra accounting
required when we actually _are_ of the fair class, it needs to
unaccount, move and reaccount.

If we're not fair, the whole switched_from/to stuff should do that for
us, no?

So please explain the problem.
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