Messages in this thread | | | Subject | Re: [patch 2/14] mm: pte prefetch | From | Arjan van de Ven <> | Date | Sun, 06 Nov 2005 09:35:01 +0100 |
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On Sun, 2005-11-06 at 19:20 +1100, Nick Piggin wrote: > 2/14 > > plain text document attachment (mm-pte-prefetch.patch) > Prefetch ptes a line ahead. Worth 25% on ia64 when doing big forks. > > Index: linux-2.6/include/asm-generic/pgtable.h > =================================================================== > --- linux-2.6.orig/include/asm-generic/pgtable.h > +++ linux-2.6/include/asm-generic/pgtable.h > @@ -196,6 +196,33 @@ static inline void ptep_set_wrprotect(st > }) > #endif > > +#ifndef __HAVE_ARCH_PTE_PREFETCH > +#define PTES_PER_LINE (L1_CACHE_BYTES / sizeof(pte_t)) > +#define PTE_LINE_MASK (~(PTES_PER_LINE - 1)) > +#define ADDR_PER_LINE (PTES_PER_LINE << PAGE_SHIFT) > +#define ADDR_LINE_MASK (~(ADDR_PER_LINE - 1)) > + > +#define pte_prefetch(pte, addr, end) \ > +({ \ > + unsigned long __nextline = ((addr) + ADDR_PER_LINE) & ADDR_LINE_MASK; \ > + if (__nextline < (end)) \ > + prefetch(pte + PTES_PER_LINE); \ > +}) > +
are you sure this is right? at least on pc's having a branch predictor miss is very expensive and might well be more expensive than the gain you get from a prefetch
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