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[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 <olof@austin.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Olof Johansson 2005-04-16 15:24:38 -07:00 committed by Linus Torvalds
parent 89e09f5ebb
commit e63f8f439d
1 changed files with 6 additions and 0 deletions
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6
include/asm-ppc64/processor.h
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@ -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));
}