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Subject[PATCH 8/9] x86/lib/memmove_64.S: Optimize memmove by enhanced REP MOVSB/STOSB
Date
From: Fenghua Yu <fenghua.yu@intel.com>

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 backward memmove case with enhanced rep movsb.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
arch/x86/lib/memmove_64.S | 29 ++++++++++++++++++++++++++++-
1 files changed, 28 insertions(+), 1 deletions(-)
diff --git a/arch/x86/lib/memmove_64.S b/arch/x86/lib/memmove_64.S
index 0ecb843..d0ec9c2 100644
--- a/arch/x86/lib/memmove_64.S
+++ b/arch/x86/lib/memmove_64.S
@@ -8,6 +8,7 @@
#define _STRING_C
#include <linux/linkage.h>
#include <asm/dwarf2.h>
+#include <asm/cpufeature.h>

#undef memmove

@@ -24,6 +25,7 @@
*/
ENTRY(memmove)
CFI_STARTPROC
+
/* Handle more 32bytes in loop */
mov %rdi, %rax
cmp $0x20, %rdx
@@ -31,8 +33,13 @@ ENTRY(memmove)

/* Decide forward/backward copy mode */
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
* so we handle small size by general register.
@@ -78,6 +85,8 @@ ENTRY(memmove)
rep movsq
movq %r11, (%r10)
jmp 13f
+.Lmemmove_end_forward:
+
/*
* Handle data backward by movsq.
*/
@@ -194,4 +203,22 @@ ENTRY(memmove)
13:
retq
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)
--
1.7.2


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