linux-kernel - Re: [PATCH] memchr (trivial) optimization

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Message-ID: <20070824021953.GG21720@waste.org>
Date:	Thu, 23 Aug 2007 21:19:53 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ingo Oeser <ioe-lkml@...eria.de>,
	lode leroy <lode_leroy@...mail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memchr (trivial) optimization

On Thu, Aug 23, 2007 at 06:03:29PM -0700, Jeremy Fitzhardinge wrote:
> Matt Mackall wrote:
> >   6e:   38 08                   cmp    %cl,(%eax)
> >   70:   74 07                   je     79 <memchr3+0x1b>
> >   72:   40                      inc    %eax
> >   
> It's a bit gross that the compiler is using inc here rather than lea or
> add, but still...
> 
> Er, something's spending 30% of its time in memchr?  This is not the
> code to fix.

Indeed. I'm just pointing out the general optimization of walking
one counter instead of two.

Hmm, perhaps the culprit is validate_nla?

-- 
Mathematics is the supreme nostalgia of our time.
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