Messages in this thread Patch in this message | | | Date | Mon, 12 Dec 2011 10:37:23 -0800 | From | tip-bot for Alexey Dobriyan <> | Subject | [tip:x86/asm] x86/i386: Use less assembly in strlen(), speed things up a bit |
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Commit-ID: 890890cb8e415e1e7a61bfe3c8e246f710196824 Gitweb: http://git.kernel.org/tip/890890cb8e415e1e7a61bfe3c8e246f710196824 Author: Alexey Dobriyan <adobriyan@gmail.com> AuthorDate: Sun, 11 Dec 2011 21:13:19 +0300 Committer: Ingo Molnar <mingo@elte.hu> CommitDate: Mon, 12 Dec 2011 18:33:42 +0100
x86/i386: Use less assembly in strlen(), speed things up a bit
Current i386 strlen() hardcodes NOT/DEC sequence. DEC is mentioned to be suboptimal on Core2. So, put only REPNE SCASB sequence in assembly, compiler can do the rest.
The difference in generated code is like below (MCORE2=y):
<strlen>: push %edi mov $0xffffffff,%ecx mov %eax,%edi xor %eax,%eax repnz scas %es:(%edi),%al not %ecx
- dec %ecx - mov %ecx,%eax + lea -0x1(%ecx),%eax
pop %edi ret
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Jan Beulich <JBeulich@suse.com> Link: http://lkml.kernel.org/r/20111211181319.GA17097@p183.telecom.by Signed-off-by: Ingo Molnar <mingo@elte.hu> --- arch/x86/lib/string_32.c | 8 +++----- 1 files changed, 3 insertions(+), 5 deletions(-)
diff --git a/arch/x86/lib/string_32.c b/arch/x86/lib/string_32.c index 82004d2..bd59090 100644 --- a/arch/x86/lib/string_32.c +++ b/arch/x86/lib/string_32.c @@ -164,15 +164,13 @@ EXPORT_SYMBOL(strchr); size_t strlen(const char *s) { int d0; - int res; + size_t res; asm volatile("repne\n\t" - "scasb\n\t" - "notl %0\n\t" - "decl %0" + "scasb" : "=c" (res), "=&D" (d0) : "1" (s), "a" (0), "0" (0xffffffffu) : "memory"); - return res; + return ~res - 1; } EXPORT_SYMBOL(strlen); #endif
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