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

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Date:	Wed, 12 Aug 2015 09:05:48 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	byungchul.park@....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 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:

/* 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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