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

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Date:	Mon, 28 Mar 2011 21:40:25 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	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>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>
Subject: Re: [PATCH 2/5] Revert "oom: give the dying task a higher priority"

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.

-- 
Kind regards,
Minchan Kim
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