[PATCH] x86_64: Undo the earlier changes to remove unrolled copy/memset functions

They cause quite bad performance regressions on Netburst
This is temporary until we can get new optimized functions
for these CPUs.

This undoes changes that were done in 2.6.15 and in 2.6.16-rc1,
essentially bringing the code back to 2.6.14 level. Only change
is I renamed the X86_FEATURE_K8_C flag to X86_FEATURE_REP_GOOD
and fixed the check for the flag and also fixed some comments.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/arch/x86_64/lib/clear_page.S b/arch/x86_64/lib/clear_page.S
index 43d9fa136180..1f81b79b796c 100644
--- a/arch/x86_64/lib/clear_page.S
+++ b/arch/x86_64/lib/clear_page.S
@@ -5,8 +5,46 @@
         .globl clear_page
         .p2align 4
 clear_page:
+        xorl   %eax,%eax
+        movl   $4096/64,%ecx
+        .p2align 4
+.Lloop:
+        decl    %ecx
+#define PUT(x) movq %rax,x*8(%rdi)
+        movq %rax,(%rdi)
+        PUT(1)
+        PUT(2)
+        PUT(3)
+        PUT(4)
+        PUT(5)
+        PUT(6)
+        PUT(7)
+        leaq    64(%rdi),%rdi
+        jnz     .Lloop
+        nop
+        ret
+clear_page_end:
+
+        /* Some CPUs run faster using the string instructions.
+           It is also a lot simpler. Use this when possible */
+
+#include <asm/cpufeature.h>
+
+        .section .altinstructions,"a"
+        .align 8
+        .quad  clear_page
+        .quad  clear_page_c
+        .byte  X86_FEATURE_REP_GOOD
+        .byte  clear_page_end-clear_page
+        .byte  clear_page_c_end-clear_page_c
+        .previous
+
+        .section .altinstr_replacement,"ax"
+clear_page_c:
         movl $4096/8,%ecx
         xorl %eax,%eax
         rep 
         stosq
         ret
+clear_page_c_end:
+        .previous