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x86, mem: memset_64.S: Optimize memset by enhanced REP MOVSB/STOSB

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Support memset() with enhanced rep stosb. On processors supporting enhanced
REP MOVSB/STOSB, the alternative memset_c_e function using enhanced rep stosb
overrides the fast string alternative memset_c and the original function.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1305671358-14478-10-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Fenghua Yu 2011-05-17 15:29:18 -07:00 committed by H. Peter Anvin
parent 057e05c1d6
commit 2f19e06ac3
1 changed files with 42 additions and 12 deletions
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54
arch/x86/lib/memset_64.S
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@ -2,9 +2,13 @@
#include <linux/linkage.h>
#include <asm/dwarf2.h>
#include <asm/cpufeature.h>
#include <asm/alternative-asm.h>
/*
* ISO C memset - set a memory block to a byte value.
* ISO C memset - set a memory block to a byte value. This function uses fast
* string to get better performance than the original function. The code is
* simpler and shorter than the orignal function as well.
*
* rdi destination
* rsi value (char)
@ -31,6 +35,28 @@
.Lmemset_e:
.previous
/*
* ISO C memset - set a memory block to a byte value. This function uses
* enhanced rep stosb to override the fast string function.
* The code is simpler and shorter than the fast string function as well.
*
* rdi destination
* rsi value (char)
* rdx count (bytes)
*
* rax original destination
*/
.section .altinstr_replacement, "ax", @progbits
.Lmemset_c_e:
movq %rdi,%r9
movb %sil,%al
movl %edx,%ecx
rep stosb
movq %r9,%rax
ret
.Lmemset_e_e:
.previous
ENTRY(memset)
ENTRY(__memset)
CFI_STARTPROC
@ -112,16 +138,20 @@ ENTRY(__memset)
ENDPROC(memset)
ENDPROC(__memset)
/* Some CPUs run faster using the string instructions.
It is also a lot simpler. Use this when possible */
#include <asm/cpufeature.h>
/* Some CPUs support enhanced REP MOVSB/STOSB feature.
* It is recommended to use this when possible.
*
* If enhanced REP MOVSB/STOSB feature is not available, use fast string
* instructions.
*
* Otherwise, use original memset function.
*
* In .altinstructions section, ERMS feature is placed after REG_GOOD
* feature to implement the right patch order.
*/
.section .altinstructions,"a"
.align 8
.quad memset
.quad .Lmemset_c
.word X86_FEATURE_REP_GOOD
.byte .Lfinal - memset
.byte .Lmemset_e - .Lmemset_c
altinstruction_entry memset,.Lmemset_c,X86_FEATURE_REP_GOOD,\
.Lfinal-memset,.Lmemset_e-.Lmemset_c
altinstruction_entry memset,.Lmemset_c_e,X86_FEATURE_ERMS, \
.Lfinal-memset,.Lmemset_e_e-.Lmemset_c_e
.previous