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

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Date:	Thu, 11 Apr 2013 17:02:38 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Mike Galbraith <efault@....de>
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 04/11/2013 04:44 PM, 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.

Agree.

>> 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.

Nice point :)

Regards,
Michael Wang

> 
> -Mike
> 

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