linux-kernel - Re: [PATCH 02/10] sched: Factor out code to should_we

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Date:	Fri, 23 Aug 2013 13:51:54 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Paul Turner <pjt@...gle.com>, Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>, Alex Shi <alex.shi@...el.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Namhyung Kim <namhyung@...nel.org>,
	Lei Wen <leiwen@...vell.com>, Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH 02/10] sched: Factor out code to should_we_balance()

On Thu, Aug 22, 2013 at 12:42:57PM +0200, Peter Zijlstra wrote:
> > >
> > > +redo:
> > 
> > One behavioral change worth noting here is that in the redo case if a
> > CPU has become idle we'll continue trying to load-balance in the
> > !new-idle case.
> > 
> > This could be unpleasant in the case where a package has a pinned busy
> > core allowing this and a newly idle cpu to start dueling for load.
> > 
> > While more deterministically bad in this case now, it could racily do
> > this before anyway so perhaps not worth worrying about immediately.
> 
> Ah, because the old code would effectively redo the check and find the
> idle cpu and thereby our cpu would no longer be the balance_cpu.
> 
> Indeed. And I don't think this was an intentional change. I'll go put
> the redo back before should_we_balance().

Ah, yes.
It isn't my intention. Please fix it.

Thanks.
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