linux-kernel - Re: [PATCH v3] sched: sync with the prev cfs when changing cgroup within a cpu

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Date:	Thu, 13 Aug 2015 08:57:41 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...nel.org, peterz@...radead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] sched: sync with the prev cfs when changing cgroup
 within a cpu

On Wed, Aug 12, 2015 at 09:05:48AM +0800, Yuyang Du wrote:
> On Wed, Aug 12, 2015 at 04:05:15PM +0900, byungchul.park@....com wrote:
> > 
> > current code seems to be wrong with cfs_rq's avg loads when changing
> > a task's cgroup(=cfs_rq) to another. i tested with "echo pid > cgroup" and
> > found that e.g. cfs_rq->avg.load_avg became larger and larger whenever i
> > changed a cgroup to another again and again.
> > 
> > we have to sync se's average load with both *prev* cfs_rq and next cfs_rq
> > when changing its group.
> > 
> 
> I think you are right in general, it has nothing to do with
> migrate_task_rq_fair() and the load should be carried to new cfs_rq.
> 
> But whether it is queued or not should be doing the same thing, so what about:

hello yuyang,

i worked with code based on torvalds git, but now.. in tip git where sched
code is renewed much, i think you are right. i will fix it.

thank you much. :)
Byungchul

> 
> /* if queued, the previous dequeue_task() should have already done it */
> if (!queued)
> 	__upload_load_avg()
> 
> remove_from_old_cfs_rq();
> 
> /* virtually catch up because of the skew between cfs_rqs */
> task's last_update_time = cfs_rq's last_update_time;
> add_to_new_cfs_rq();
> 
> Thanks,
> Yuyang
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