linux-kernel - Re: [patch] sched: minimalist select_idle

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Message-ID: <20130128112145.GA23495@gmail.com>
Date:	Mon, 28 Jan 2013 12:21:45 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mike Galbraith <bitbucket@...ine.de>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [patch] sched: minimalist select_idle_sibling() bouncing cow
 syndrome fix


* Mike Galbraith <bitbucket@...ine.de> wrote:

> On Mon, 2013-01-28 at 11:53 +0100, Ingo Molnar wrote: 
> > * Mike Galbraith <bitbucket@...ine.de> wrote:
> > 
> > > If the previous CPU is cache affine and idle, select it.
> > 
> > No objections in principle - but would be nice to have a 
> > changelog with numbers, % of improvement included and so?
> 
> Well, that like was my changelog, guess it needs improvement.
> 
> Take 2.
> 
> sched: minimalist select_idle_sibling() bouncing cow syndrome fix
> 
> If the previous CPU is cache affine and idle, select it.
> 
> The current implementation simply traverses the sd_llc domain,
> taking the first idle CPU encountered, which walks buddy pairs
> hand in hand over the package, inflicting excruciating pain.
> 
> 1 tbench pair (worst case) in a 10 core + SMT package:
> 
> pre   15.22 MB/sec 1 procs
> post 252.01 MB/sec 1 procs

Drool ... :-)

What would be a 'contrarian' test - i.e. a test where this could 
hurt most?

Thanks,

	Ingo
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