linux-kernel - Re: [PATCH v2] proc: speedup /proc/stat handling

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Message-Id: <20120125170416.385ee9fa.akpm@linux-foundation.org>
Date:	Wed, 25 Jan 2012 17:04:16 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Glauber Costa <glommer@...allels.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Paul Tuner <pjt@...gle.com>
Subject: Re: [PATCH v2] proc:  speedup /proc/stat handling

On Wed, 25 Jan 2012 06:29:32 +0100
Eric Dumazet <eric.dumazet@...il.com> wrote:

> Le mardi 24 janvier 2012 __ 17:27 -0800, Andrew Morton a __crit :
> 
> > I had a fiddle on an 8-way x86_64 machine.  I'm unable to demonstrate
> > any improvement for either of
> > 
> > time (for i in $(seq 1000); do; cat /proc/self/stat > /dev/null; done)
> > time (for i in $(seq 1000); do; cat /proc/1/stat > /dev/null; done)
> > 
> > oh well.
> 
> What size is /proc/stat ?

About 40mm, but it depends on the font size.

> wc -c /proc/stat
> 
> If under 4096, there is no problem with existing code.

akpm2:/home/akpm> wc -c /proc/stat 
2800 /proc/stat

> I had the problem on a 16-way machine.

OK..
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