linux-kernel - Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets

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Message-ID: <1348502863.11847.92.camel@twins>
Date:	Mon, 24 Sep 2012 18:07:43 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mel Gorman <mgorman@...e.de>, Borislav Petkov <bp@...en8.de>,
	Nikolay Ulyanitsky <lystor@...il.com>,
	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to
 3.6-rc5 on AMD chipsets - bisected

On Mon, 2012-09-24 at 08:52 -0700, Linus Torvalds wrote:
> Your patch looks odd, though. Why do you use some complex initial
> value for 'candidate' (nr_cpu_ids) instead of a simple and readable
> one (-1)? 

nr_cpu_ids is the typical no-value value for cpumask operations -- yes
this is annoying and I keep doing it wrong far too often.
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