Re: [PATCH 3/2] Use strspn/strcspn/strpbrk ifunc in internal calls.

[Mike Frysinger <vapier at gentoo dot org>]

On 18 Mar 2014 11:01, OndÅej BÃlka wrote:
> To make a strtok faster and improve performance in general we need to do one
> additional change.
> 
> A comment:
> 
> /* It doesn't make sense to send libc-internal strcspn calls through a PLT.
>    The speedup we get from using SSE4.2 instruction is likely eaten away
>    by the indirect call in the PLT.  */
> 
> Does not make sense at all because nobody bothered to check it. Gap
> between these implementations is quite big, when haystack is empty a
> sse2 is around 40 cycles slower because it needs to populate a lookup
> table and difference only increases with size. That is much bigger than
> plt slowdown which is few cycles.
> 
> Even benchtest show a gap which also may be reverse by branch
> misprediction but my internal benchmark shown.
> 
>  simple_strspn stupid_strspn __strspn_sse42  __strspn_sse2
> Length    0, alignment  0, acc len  6:  18.6562 35.2344 17.0469 61.6719
> Length    6, alignment  0, acc len  6:  59.5469 72.5781 16.4219 73.625
> 
> This patch also handles strpbrk which is implemented by including a
> x86_64/multiarch/strcspn.S file.
> 
> 	* sysdeps/x86_64/multiarch/strspn.S: Remove plt indirection.
> 	* sysdeps/x86_64/multiarch/strcspn.S: Likewise.

since H.J. wrote the code, he probably should be the one approving this change
-mike

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