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

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Oct 05, 2015 at 06:16:23PM +0900, byungchul.park@lge.com wrote:
> From: Byungchul Park <byungchul.park@lge.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.