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

[OndÅej BÃlka <neleai at seznam dot cz>]

ping
On Tue, Mar 18, 2014 at 11:01:38AM +0100, 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.
> 
> diff --git a/sysdeps/x86_64/multiarch/strcspn.S b/sysdeps/x86_64/multiarch/strcspn.S
> index 24f55e9..1b3e1aa 100644
> --- a/sysdeps/x86_64/multiarch/strcspn.S
> +++ b/sysdeps/x86_64/multiarch/strcspn.S
> @@ -65,14 +65,7 @@ END(STRCSPN)
>  # undef END
>  # define END(name) \
>  	cfi_endproc; .size STRCSPN_SSE2, .-STRCSPN_SSE2
> -# undef libc_hidden_builtin_def
> -/* 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.  */
> -# define libc_hidden_builtin_def(name) \
> -	.globl __GI_STRCSPN; __GI_STRCSPN = STRCSPN_SSE2
>  #endif
> -
>  #endif /* HAVE_SSE4_SUPPORT */
>  
>  #ifdef USE_AS_STRPBRK
> diff --git a/sysdeps/x86_64/multiarch/strspn.S b/sysdeps/x86_64/multiarch/strspn.S
> index bf7308e..fde1e1e 100644
> --- a/sysdeps/x86_64/multiarch/strspn.S
> +++ b/sysdeps/x86_64/multiarch/strspn.S
> @@ -50,12 +50,6 @@ END(strspn)
>  # undef END
>  # define END(name) \
>  	cfi_endproc; .size __strspn_sse2, .-__strspn_sse2
> -# undef libc_hidden_builtin_def
> -/* It doesn't make sense to send libc-internal strspn calls through a PLT.
> -   The speedup we get from using SSE4.2 instruction is likely eaten away
> -   by the indirect call in the PLT.  */
> -# define libc_hidden_builtin_def(name) \
> -	.globl __GI_strspn; __GI_strspn = __strspn_sse2
>  #endif
>  
>  #endif /* HAVE_SSE4_SUPPORT */

-- 

Too many little pins on CPU confusing it, bend back and forth until 10-20% are neatly removed. Do _not_ leave metal bits visible!