The source code is already hard to maintain. I think the more macros, uncommon and compiler specific things we have in there, the harder it will get. That's why I think that if it doesn't give much benefit it actually hurts to have it in because maintenance keeps on getting harder. Again, I think it's a cool effort by Nuno and I'll be interested to watch more fine-tuned results but I've been down this patch and it seems the CPUs do their work fairly OK.
>-----Original Message----- >From: Zeev Suraski [mailto:[EMAIL PROTECTED] >Sent: Tuesday, June 20, 2006 7:17 AM >To: Andi Gutmans >Cc: 'Nuno Lopes'; 'PHPdev' >Subject: RE: [PHP-DEV] messing with branch prediction > >I still don't see how it can hurt, and even if it doesn't do >anything performance wise, it adds clarity to the code. > >Zeev > >At 20:34 19/06/2006, Andi Gutmans wrote: >>I think it's a nice idea but I doubt it's very useful at this >point. It >>doesn't seem to significantly affect performance, which is >inline with >>some tests that we have done in the past, where it's really the >>hardware management of branch prediction and cache size which affect >>this. I doubt that make such code changes will affect that in >a significant way. >>We are playing around with some memory management issues, and are >>relying on some hardware branch predicition there (i.e. >hoping that the >>hardware will play nice with if() statements that always evaluate the >>same). It seems that the hardware is playing pretty nice with us. >> >> >> >-----Original Message----- >> >From: Zeev Suraski [mailto:[EMAIL PROTECTED] >> >Sent: Monday, June 19, 2006 12:46 AM >> >To: Nuno Lopes >> >Cc: PHPdev >> >Subject: Re: [PHP-DEV] messing with branch prediction >> > >> >Definitely looks nice. I actually like how it makes the code more >> >readable hinting which branches are rare. >> > >> >Zeev >> > >> >At 16:49 18/06/2006, 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_00 >> >>5fbuiltin_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 >> >>-- >> >>PHP Internals - PHP Runtime Development Mailing List To >unsubscribe, >> >>visit: http://www.php.net/unsub.php >> > >> >-- >> >PHP Internals - PHP Runtime Development Mailing List To >unsubscribe, >> >visit: http://www.php.net/unsub.php >> > > -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
