linux-kernel - Re: [PATCH] sched: sync with the prev cfs when changing cgroup within a cpu

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Date:	Tue, 11 Aug 2015 09:01:57 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: sync with the prev cfs when changing cgroup
 within a cpu

On Mon, Aug 10, 2015 at 01:47:06PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 10, 2015 at 03:08:59PM +0900, byungchul.park@....com wrote:
> > From: Byungchul Park <byungchul.park@....com>
> > 
> > in addition, "#ifdef CONFIG_SMP" is removed becasuse we need to sync a
> > se's load with its cfs_rq even in the case of !SMP. remember it is possible
> > to move between groups in *a* cpu.

if it never need to keep the blocked load in the case of !SMP, then i will undo
this part, and add "#ifdef" to my additional code.

commit message below is for explaining the reason why i removed some comments.
not much about code work.

> > 
> > i also removed some comments mentioning migration_task_rq_fair().
> > migration_task_rq_fair() can be called in three cases. and in each case,
> > both decay counter and blocked load are already considered. so we
> > don't need to consider these in task_move_group_fair() at all.
> > 
> > 1. the wake-up migration case
> > enqueue_entity_load_avg() makes se->avg.decay_count zero after applying it.
> > and it will be woken up soon so we don't need to add its load to
> > cfs_rq->blocked_load_avg.
> > 
> > 2. the fork balancing case
> > se->avg.decay_count is initialized in __sched_fork() to zero. and
> > wake_up_new_task() calls activate_task() with flag = 0 so that
> > enqueue_entity_load_avg() can omit adding its load to
> > cfs_rq->blocked_load_avg, and it will be woken up soon.
> > 
> > 3. the rq migration case (not wake up case)
> > the target task is already on rq, so we don't need to consider both its
> > decay counter and blocked load in this case.
> > 
> > Signed-off-by: Byungchul Park <byungchul.park@....com>
> 
> What code is this against? Please look at current code and try again.
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