linux-kernel - Re: [PATCH] sched: wakeup buddy

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Date:	Fri, 08 Mar 2013 10:37:23 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Mike Galbraith <efault@....de>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Alex Shi <alex.shi@...el.com>, 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: wakeup buddy

On 03/07/2013 05:43 PM, Mike Galbraith wrote:
> On Thu, 2013-03-07 at 09:36 +0100, Peter Zijlstra wrote: 
>> On Wed, 2013-03-06 at 15:06 +0800, Michael Wang wrote:
>>
>>> wake_affine() stuff is trying to bind related tasks closely, but it doesn't
>>> work well according to the test on 'perf bench sched pipe' (thanks to Peter).
>>
>> so sched-pipe is a poor benchmark for this.. 
>>
>> Ideally we'd write a new benchmark that has some actual data footprint
>> and we'd measure the cost of tasks being apart on the various cache
>> metrics and see what affine wakeup does for it.
>>
>> Before doing something like what you're proposing, I'd have a hard look
>> at WF_SYNC, it is possible we should disable/fix select_idle_sibling
>> for sync wakeups.
> 
> If nobody beats me to it, I'm going to try tracking shortest round trip
> to idle, and use a multiple of that to shut select_idle_sibling() down.
> If avg_idle approaches round trip time, there's no win to be had, we're
> just wasting cycles.

That's great if we have it, I'm a little doubt whether it is possible to
find a better way to replace the select_idle_sibling() (look at the way
it locates idle cpu...) in some cases, but I'm looking forward it ;-)

Regards,
Michael Wang

> 
> -Mike
> 
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