x86, mem: memmove_64.S: Optimize memmove by enhanced REP MOVSB/STOSB
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>
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 @@
/* 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 @@
rep movsq
movq %r11, (%r10)
jmp 13f
+.Lmemmove_end_forward:
+
/*
* Handle data backward by movsq.
*/
@@ -194,4 +203,22 @@
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)