linux-kernel - Re: Linux doesn't follow x86/x86-64 ABI wrt direction flag

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Date:	Fri, 7 Mar 2008 15:09:40 +0100 (CET)
From:	Michael Matz <matz@...e.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Richard Guenther <richard.guenther@...il.com>,
	Joe Buck <Joe.Buck@...opsys.com>,
	Andrew Haley <aph@...hat.com>,
	Aurelien Jarno <aurelien@...el32.net>,
	linux-kernel@...r.kernel.org, gcc@....gnu.org
Subject: Re: Linux doesn't follow x86/x86-64 ABI wrt direction flag

Hi,

On Thu, 6 Mar 2008, Andi Kleen wrote:

> To be realistic it is very unlikely anybody will measure a difference 
> from a few more or a few less clds in a program.

Only an assumption, and in fact wrong.  See upthread for a benchmark.  
IIRC Uros also made measurements to justify the removal of cld (on P4 I 
think), where it helps tremendously on small memcpy loops.


Ciao,
Michael.
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