From e63f8f439de010b6227c0c9c6f56e2c44dbe5dae Mon Sep 17 00:00:00 2001 From: Olof Johansson Date: Sat, 16 Apr 2005 15:24:38 -0700 Subject: [PATCH] [PATCH] ppc64: no prefetch for NULL pointers For prefetches of NULL (as when walking a short linked list), PPC64 will in some cases take a performance hit. The hardware needs to do the TLB walk, and said walk will always miss, which means (up to) two L2 misses as penalty. This seems to hurt overall performance, so for NULL pointers skip the prefetch alltogether. Signed-off-by: Olof Johansson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/asm-ppc64/processor.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/asm-ppc64/processor.h b/include/asm-ppc64/processor.h index eb33d33cfd6d..cae65b30adb8 100644 --- a/include/asm-ppc64/processor.h +++ b/include/asm-ppc64/processor.h @@ -642,11 +642,17 @@ static inline unsigned long __pack_fe01(unsigned int fpmode) static inline void prefetch(const void *x) { + if (unlikely(!x)) + return; + __asm__ __volatile__ ("dcbt 0,%0" : : "r" (x)); } static inline void prefetchw(const void *x) { + if (unlikely(!x)) + return; + __asm__ __volatile__ ("dcbtst 0,%0" : : "r" (x)); }