linux-kernel - Re: [PATCH] sched: wake-affine throttle

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Message-ID: <1365670840.19620.132.camel@marge.simpson.net>
Date:	Thu, 11 Apr 2013 11:00:40 +0200
From:	Mike Galbraith <efault@....de>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Alex Shi <alex.shi@...el.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Turner <pjt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Ram Pai <linuxram@...ibm.com>
Subject: Re: [PATCH] sched: wake-affine throttle

On Thu, 2013-04-11 at 10:44 +0200, Mike Galbraith wrote: 
> On Thu, 2013-04-11 at 16:26 +0800, Michael Wang wrote:
> 
> > The 1:N is a good reason to explain why the chance that wakee's hot data
> > cached on curr_cpu is lower, and since it's just 'lower' not 'extinct',
> > after the throttle interval large enough, it will be balanced, this
> > could be proved, since during my test, when the interval become too big,
> > the improvement start to drop.
> 
> Magnitude of improvement drops just because there's less damage done
> methinks.  You'll eventually run out of measurable damage :)
> 
> Yes, it's not really extinct, you _can_ reap a gain, it's just not at
> all likely to work out.  A more symetric load will fare better, but any
> 1:N thing just has to spread far and wide to have any chance to perform.
> > Hmm...that's an interesting point, the workload contain different
> > 'priority' works, and depend on each other, if mother starving, all the
> > kids could do nothing but wait for her, may be that's the reason why the
> > benefit is so significant, since in such case, mother's little quicker
> > respond will make all the kids happy :)
> 
> Exactly.  The entire load is server latency bound.  Keep the server on
> cpu, the load performs as best it can given unavoidable data miss cost.

(ie serial producer, parallel consumer... choke point lies with utterly
unscalable serial work producer)

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