[PATCH] x86_64: prefetchw() can fall back to prefetch() if !3DNOW

This is a multi-part message in MIME format.  If the cpu lacks 3DNOW
feature, we can use a normal prefetcht0 instruction instead of NOP5.
"prefetchw (%rxx)" and "prefetcht0 (%rxx)" have the same length, ranging
from 3 to 5 bytes depending on the register.  So this patch even helps
AMD64, shortening the length of the code.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/include/asm-x86_64/processor.h b/include/asm-x86_64/processor.h
index 194160f..a832199 100644 (file)
--- a/include/asm-x86_64/processor.h
+++ b/include/asm-x86_64/processor.h
@@ -398,7 +398,7 @@ static inline void prefetch(void *x)
 #define ARCH_HAS_PREFETCHW 1
 static inline void prefetchw(void *x) 
 { 
-       alternative_input(ASM_NOP5,
+       alternative_input("prefetcht0 (%1)",
                          "prefetchw (%1)",
                          X86_FEATURE_3DNOW,
                          "r" (x));