Re: [PATCH] x86_64/lib: improve the performance of memmove

[Miao Xie <miaox@cn.fujitsu.com>]

On Thu, 16 Sep 2010 12:11:41 +0200, Andi Kleen wrote:
> On Thu, 16 Sep 2010 17:29:32 +0800
> Miao Xie<miaox@cn.fujitsu.com>  wrote:
>
>
> Ok was a very broken patch. Sorry should have really done some more
> work on it. Anyways hopefully the corrected version is good for
> testing.
>
> -Andi
>

title: x86_64/lib: improve the performance of memmove

Implement the 64bit memmmove backwards case using string instructions

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
---
  arch/x86/lib/memcpy_64.S  |   29 +++++++++++++++++++++++++++++
  arch/x86/lib/memmove_64.c |    8 ++++----
  2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
index bcbcd1e..9de5e9a 100644
--- a/arch/x86/lib/memcpy_64.S
+++ b/arch/x86/lib/memcpy_64.S
@@ -141,3 +141,32 @@ ENDPROC(__memcpy)
  	.byte .Lmemcpy_e - .Lmemcpy_c
  	.byte .Lmemcpy_e - .Lmemcpy_c
  	.previous
+
+/*
+ * Copy memory backwards (for memmove)
+ * rdi target
+ * rsi source
+ * rdx count
+ */
+
+ENTRY(memcpy_backwards)
+	CFI_STARTPROC
+	std
+	movq %rdi, %rax
+	movl %edx, %ecx
+	addq %rdx, %rdi
+	addq %rdx, %rsi
+	leaq -8(%rdi), %rdi
+	leaq -8(%rsi), %rsi
+	shrl $3, %ecx
+	andl $7, %edx
+	rep movsq
+	addq $7, %rdi
+	addq $7, %rsi
+	movl %edx, %ecx
+	rep movsb
+	cld
+	ret
+	CFI_ENDPROC
+ENDPROC(memcpy_backwards)
+	
diff --git a/arch/x86/lib/memmove_64.c b/arch/x86/lib/memmove_64.c
index 0a33909..6774fd8 100644
--- a/arch/x86/lib/memmove_64.c
+++ b/arch/x86/lib/memmove_64.c
@@ -5,16 +5,16 @@
  #include <linux/string.h>
  #include <linux/module.h>
  
+extern void * asmlinkage memcpy_backwards(void *dst, const void *src,
+				        size_t count);
+
  #undef memmove
  void *memmove(void *dest, const void *src, size_t count)
  {
  	if (dest < src) {
  		return memcpy(dest, src, count);
  	} else {
-		char *p = dest + count;
-		const char *s = src + count;
-		while (count--)
-			*--p = *--s;
+		return memcpy_backwards(dest, src, count);
  	}
  	return dest;
  }
-- 
1.7.0.1