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x86, mem: memmove_64.S: Optimize memmove by enhanced REP MOVSB/STOSB

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Support memmove() by enhanced rep movsb. On processors supporting enhanced
REP MOVSB/STOSB, the alternative memmove() function using enhanced rep movsb
overrides the original function.

The patch doesn't change the backward memmove case to use enhanced rep
movsb.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1305671358-14478-9-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 15:29:17 -07:00 committed by H. Peter Anvin
parent 101068c1f4
commit 057e05c1d6
1 changed files with 28 additions and 1 deletions
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29
arch/x86/lib/memmove_64.S
View file

@ -8,6 +8,7 @@
#define _STRING_C #define _STRING_C
#include <linux/linkage.h> #include <linux/linkage.h>
#include <asm/dwarf2.h> #include <asm/dwarf2.h>
#include <asm/cpufeature.h>
#undef memmove #undef memmove
@ -24,6 +25,7 @@
*/ */
ENTRY(memmove) ENTRY(memmove)
CFI_STARTPROC CFI_STARTPROC
/* Handle more 32bytes in loop */ /* Handle more 32bytes in loop */
mov %rdi, %rax mov %rdi, %rax
cmp $0x20, %rdx cmp $0x20, %rdx
@ -31,8 +33,13 @@ ENTRY(memmove)
/* Decide forward/backward copy mode */ /* Decide forward/backward copy mode */
cmp %rdi, %rsi cmp %rdi, %rsi
jb 2f jge .Lmemmove_begin_forward
mov %rsi, %r8
add %rdx, %r8
cmp %rdi, %r8
jg 2f
.Lmemmove_begin_forward:
/* /*
* movsq instruction have many startup latency * movsq instruction have many startup latency
* so we handle small size by general register. * so we handle small size by general register.
@ -78,6 +85,8 @@ ENTRY(memmove)
rep movsq rep movsq
movq %r11, (%r10) movq %r11, (%r10)
jmp 13f jmp 13f
.Lmemmove_end_forward:
/* /*
* Handle data backward by movsq. * Handle data backward by movsq.
*/ */
@ -194,4 +203,22 @@ ENTRY(memmove)
13: 13:
retq retq
CFI_ENDPROC CFI_ENDPROC
.section .altinstr_replacement,"ax"
.Lmemmove_begin_forward_efs:
/* Forward moving data. */
movq %rdx, %rcx
rep movsb
retq
.Lmemmove_end_forward_efs:
.previous
.section .altinstructions,"a"
.align 8
.quad .Lmemmove_begin_forward
.quad .Lmemmove_begin_forward_efs
.word X86_FEATURE_ERMS
.byte .Lmemmove_end_forward-.Lmemmove_begin_forward
.byte .Lmemmove_end_forward_efs-.Lmemmove_begin_forward_efs
.previous
ENDPROC(memmove) ENDPROC(memmove)