linux-kernel - Re: [PATCH v4 0/5] sync a se with its cfs

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Date:	Sat, 22 Aug 2015 16:45:34 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	mingo@...nel.org, peterz@...radead.org
Cc:	linux-kernel@...r.kernel.org, yuyang.du@...el.com
Subject: Re: [PATCH v4 0/5] sync a se with its cfs_rq when att(det)aching it

On Thu, Aug 20, 2015 at 08:21:55PM +0900, byungchul.park@....com wrote:
> From: Byungchul Park <byungchul.park@....com>

i am not sure if i did it here, in v4, as peter suggested fully. i did
not fully undertand what he commented on v3. i am waiting for any
feedback e.g. answering to my question, just reviewing now and so on.

> 
> there are 3 problems when att(det)aching a se to(from) its cfs_rq.
> 
> problem 1. se's average load is not accounted with new cfs_rq in queued case,
> when a task changes its cgroup.
> 
> problem 2. cfs_rq->avg.load_avg becomes larger and larger whenever changing
> cgroup to another. we have to sync se's average load with prev cfs_rq.
> 
> problem 3. current code does not sync it with its cfs_rq when switching
> sched class to fair class. if we can always assume that a se has been
> detached from fair class for a long time enough for its average load to
> become useless, at the time attaching it to its fair class cfs_rq, then
> current code is acceptable. but the assumption is not always true.
> 
> patch 1/5, does code refactoring for further patches.
> patch 2/5, solves the problem 1.
> patch 3/5, solves the problem 2.
> patch 4/5, solves the problem 3.
> patch 5/5, does code refactoring for better readability.
> 
> change from v3 to v4
> * clean up code as Peter suggests
> * use upper case letter in comment properly
> 
> change from v2 to v3 (logic is same as v2)
> * fix up my poor english in commit message and comment
> * break down big patches into more patches for being reviewed easily
> * supplement cover letter messages
> 
> change from v1 to v2
> * introduce two functions for adjusting vruntime and load when attaching
>   and detaching.
> * call the introduced functions instead of switched_from(to)_fair() directly
>   in task_move_group_fair().
> * add decaying logic for a se which has detached from a cfs_rq.
> 
> thanks,
> byungchul
> 
> Byungchul Park (5):
>   sched: add two functions adjusting cfs_rq's load when att(det)aching
>     a se
>   sched: make task_move_group_fair adjust cfs_rq's load in case of
>     queued
>   sched: sync a se with prev cfs_rq when changing cgroup
>   sched: sync a se with its cfs_rq when switching sched class to fair
>     class
>   sched: add two functions for att(det)aching a task to(from) a cfs_rq
> 
>  kernel/sched/fair.c |  222 ++++++++++++++++++++++++++-------------------------
>  1 file changed, 113 insertions(+), 109 deletions(-)
> 
> -- 
> 1.7.9.5
> 
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