mirror/glibc
2
0
Fork 0
mirror of git://sourceware.org/git/glibc.git synced 2025-03-31 14:01:18 +08:00
Code Issues Packages Projects Releases Wiki Activity

Use strspn/strcspn/strpbrk ifunc in internal calls.

Browse Source 
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.
This commit is contained in:
Ondřej Bílka 2014-03-18 11:01:38 +01:00
parent 7327b333e5
commit 0f4840be25
3 changed files with 5 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
ChangeLog
View File

@ -1,3 +1,8 @@
2015-05-12 Ondřej Bílka <neleai@seznam.cz>
* sysdeps/x86_64/multiarch/strcspn.S: Remove plt indirection.
* sysdeps/x86_64/multiarch/strspn.S: Likewise.
2015-05-12 Roland McGrath <roland@hack.frob.com>
* posix/uname-values.h: New file.

7
sysdeps/x86_64/multiarch/strcspn.S
View File

@ -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

6
sysdeps/x86_64/multiarch/strspn.S
View File

@ -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 */