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

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Date:	Thu, 07 Mar 2013 10:43:39 +0100
From:	Mike Galbraith <efault@....de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Michael Wang <wangyun@...ux.vnet.ibm.com>,
	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 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.

-Mike

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