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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