Commit e365c9df authored by Fenghua Yu's avatar Fenghua Yu Committed by H. Peter Anvin
Browse files

x86, mem: clear_page_64.S: Support clear_page() with enhanced REP MOVSB/STOSB 



Intel processors are adding enhancements to REP MOVSB/STOSB and the use of
REP MOVSB/STOSB for optimal memcpy/memset or similar functions is recommended.
Enhancement availability is indicated by CPUID.7.0.EBX[9] (Enhanced REP MOVSB/
STOSB).

Support clear_page() with rep stosb for processor supporting enhanced REP MOVSB
/STOSB. On processors supporting enhanced REP MOVSB/STOSB, the alternative
clear_page_c_e function using enhanced REP STOSB overrides the original function
and the fast string function.

Signed-off-by: default avatarFenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1305671358-14478-6-git-send-email-fenghua.yu@intel.com


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 9072d11d

arch/x86/lib/clear_page_64.S

+24 −9
Original line number Original line Diff line number Diff line 
#include <linux/linkage.h>

#include <linux/linkage.h>

#include <asm/dwarf2.h>

#include <asm/dwarf2.h>

#include <asm/alternative-asm.h>





/*

/*

 * Zero a page. 	

 * Zero a page.
@@ -14,6 +15,15 @@ ENTRY(clear_page_c) 
	CFI_ENDPROC

	CFI_ENDPROC

ENDPROC(clear_page_c)

ENDPROC(clear_page_c)





ENTRY(clear_page_c_e)

	CFI_STARTPROC

	movl $4096,%ecx

	xorl %eax,%eax

	rep stosb

	ret

	CFI_ENDPROC

ENDPROC(clear_page_c_e)



ENTRY(clear_page)

ENTRY(clear_page)

	CFI_STARTPROC

	CFI_STARTPROC

	xorl   %eax,%eax

	xorl   %eax,%eax
@@ -38,21 +48,26 @@ ENTRY(clear_page) 
.Lclear_page_end:

.Lclear_page_end:

ENDPROC(clear_page)

ENDPROC(clear_page)





	/* Some CPUs run faster using the string instructions.

	/*

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

	 * Some CPUs support enhanced REP MOVSB/STOSB instructions.

	 * It is recommended to use this when possible.

	 * If enhanced REP MOVSB/STOSB is not available, try to use fast string.

	 * Otherwise, use original function.

	 *

	 */





#include <asm/cpufeature.h>

#include <asm/cpufeature.h>





	.section .altinstr_replacement,"ax"

	.section .altinstr_replacement,"ax"

1:	.byte 0xeb					/* jmp <disp8> */

1:	.byte 0xeb					/* jmp <disp8> */

	.byte (clear_page_c - clear_page) - (2f - 1b)	/* offset */

	.byte (clear_page_c - clear_page) - (2f - 1b)	/* offset */

2:

2:	.byte 0xeb					/* jmp <disp8> */

	.byte (clear_page_c_e - clear_page) - (3f - 2b)	/* offset */

3:

	.previous

	.previous

	.section .altinstructions,"a"

	.section .altinstructions,"a"

	.align 8

	altinstruction_entry clear_page,1b,X86_FEATURE_REP_GOOD,\

	.quad clear_page

			     .Lclear_page_end-clear_page, 2b-1b

	.quad 1b

	altinstruction_entry clear_page,2b,X86_FEATURE_ERMS,   \

	.word X86_FEATURE_REP_GOOD

			     .Lclear_page_end-clear_page,3b-2b

	.byte .Lclear_page_end - clear_page

	.byte 2b - 1b

	.previous
 
	.previous

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