linux-kernel - Re: [PATCH 2/5] Revert "oom: give the dying task a higher priority"

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Date:	Mon, 28 Mar 2011 10:10:29 -0300
From:	"Luis Claudio R. Goncalves" <lclaudio@...g.org>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-mm <linux-mm@...ck.org>,
	Andrey Vagin <avagin@...nvz.org>,
	Hugh Dickins <hughd@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 2/5] Revert "oom: give the dying task a higher priority"

On Mon, Mar 28, 2011 at 09:40:25PM +0900, Minchan Kim wrote:
| On Mon, Mar 28, 2011 at 02:28:27PM +0200, Peter Zijlstra wrote:
| > On Mon, 2011-03-28 at 21:21 +0900, Minchan Kim wrote:
| > > Hi Peter,
| > > 
| > > On Mon, Mar 28, 2011 at 11:51:36AM +0200, Peter Zijlstra wrote:
| > > > On Fri, 2011-03-25 at 00:27 +0900, Minchan Kim wrote:
| > > > > 
| > > > > At that time, I thought that routine is meaningless in non-RT scheduler.
| > > > > So I Cced Peter but don't get the answer.
| > > > > I just want to confirm it. 
| > > > 
| > > > Probably lost somewhere in the mess that is my inbox :/, what is the
| > > > full question?
| > > 
| > > The question is we had a routine which change rt.time_slice with HZ to 
| > > accelarate task exit. But when we applied 93b43fa5508, we found it isn't effective
| > > any more about normal task. So we removed it. Is it right?
| > 
| > rt.time_slice is only relevant to SCHED_RR, since you seem to use
| > SCHED_FIFO (which runs for as long as the task is runnable), its
| > completely irrelevant.
| > 
| > > And Kosaki is about to revert 93b43fa5508 to find out the problem of this thread
| > > and Luis said he has a another solution to replace 93b43fa5508. 
| > > If rt.time_slice handleing is effective, we should restore it until Luis's patch
| > > will be merged.
| > 
| > Right, so only SCHED_RR is affected by time_slice, it will be
| > decremented on tick (so anything that avoids ticks will also avoid the
| > decrement) and once it reaches 0 the task will be queued at the tail of
| > its static priority and reset the slice. If there is no other task on
| > that same priority we'll again schedule that task.
| > 
| > In short, don't use SCHED_RR and don't worry about time_slice.
| 
| There was meaningless code in there. I guess it was in there from CFS.
| Thanks for the explanation, Peter.

Yes, it was CFS related:

	p = find_lock_task_mm(p);
	...
	p->rt.time_slice = HZ; <<---- THIS

Peter, would that be effective to boost the priority of the dying task?
I mean, in the context of SCHED_OTHER tasks would it really help the dying
task to be scheduled sooner to release its resources? If so, as we remove
the code in commit 93b43fa5508 we should re-add that old code.

Luis
-- 
[ Luis Claudio R. Goncalves             Red Hat  -  Realtime Team ]
[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]

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