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Cc: "PHPdev" <internals@lists.php.net>,
  <andi@php.net>,
  <dmitry@php.net>
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Date: Sun, 18 Jun 2006 22:02:34 -0400
To: Nuno Lopes <nlopess@php.net>
Sender: Ilia Alshanetsky <iliaal@gmail.com>
Subject: Re: [PHP-DEV] messing with branch prediction
From: ilia@prohost.org (Ilia Alshanetsky)

Looks like an interesting patch, if it does not cost us any  
performance and only offers either no gain or a small gain I'd say it  
would be worth inclusion. Perhaps branch prediction will work better  
with newer versions of gcc like 4.0 or 4.1


On 18-Jun-06, at 9:49 AM, Nuno Lopes wrote:

> Hello,
>
> Yesterday I was playing with branch prediction in the Zend VM  
> executor. Although I didn't have any noticeable performance  
> improvement within the bench.php script, I've put the patch on- 
> line, because someone else might want to mess with it too :) (but  
> with care..)
>
> patch: http://mega.ist.utl.pt/~ncpl/zend_branch_prediction.txt
> gcc docs: http://gcc.gnu.org/onlinedocs/gcc/Other- 
> Builtins.html#index-g_t_005f_005fbuiltin_005fexpect-2440
>
> the zend.h part of the patch is based on the similar macros (with  
> the same name, too) found in the Linux kernel.
>
> I made & tested the patch in a Centrino laptop with gcc 3.4, so it  
> might be the cause of getting no relevant performance increase. On  
> CPUs with longer pipelines (like Pentium 4/NetBurst architecture),  
> the performance increase might be noticeable.
>
>
> Happy hacking :)
> Nuno
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>

Ilia Alshanetsky