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Commit 2f19e06a authored by Fenghua Yu's avatar Fenghua Yu Committed by H. Peter Anvin
Browse files

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



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: default avatarFenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1305671358-14478-10-git-send-email-fenghua.yu@intel.com


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 057e05c1

arch/x86/lib/memset_64.S

+42 −12
Original line number Original line Diff line number Diff line
@@ -2,9 +2,13 @@ 




#include <linux/linkage.h>

#include <linux/linkage.h>

#include <asm/dwarf2.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

 * rdi   destination

 * rsi   value (char) 

 * rsi   value (char)
@@ -31,6 +35,28 @@ 
.Lmemset_e:

.Lmemset_e:

	.previous

	.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)

ENTRY(__memset)

ENTRY(__memset)

	CFI_STARTPROC

	CFI_STARTPROC
@@ -112,16 +138,20 @@ ENTRY(__memset) 
ENDPROC(memset)

ENDPROC(memset)

ENDPROC(__memset)

ENDPROC(__memset)





	/* Some CPUs run faster using the string instructions.

	/* Some CPUs support enhanced REP MOVSB/STOSB feature.

	   It is also a lot simpler. Use this when possible */

	 * It is recommended to use this when possible.



	 *

#include <asm/cpufeature.h>

	 * 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"

	.section .altinstructions,"a"

	.align 8

	altinstruction_entry memset,.Lmemset_c,X86_FEATURE_REP_GOOD,\

	.quad memset

			     .Lfinal-memset,.Lmemset_e-.Lmemset_c

	.quad .Lmemset_c

	altinstruction_entry memset,.Lmemset_c_e,X86_FEATURE_ERMS, \

	.word X86_FEATURE_REP_GOOD

			     .Lfinal-memset,.Lmemset_e_e-.Lmemset_c_e

	.byte .Lfinal - memset

	.byte .Lmemset_e - .Lmemset_c

	.previous
 
	.previous