Messages in this thread Patch in this message | | | Date | Fri, 29 Jul 2005 09:07:02 +0200 | From | Ingo Molnar <> | Subject | Re: Add prefetch switch stack hook in scheduler function |
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* Ingo Molnar <mingo@elte.hu> wrote:
> > Sorry, this is not enough. Switch stack on ia64 is 528 bytes. We > > need to prefetch 5 lines. It probably should use prefetch_range(). > > ok, how about the additional patch below? Does this do the trick on > ia64? It makes complete sense on every architecture to prefetch from > below the current kernel stack, in the expectation of the next task > touching the stack. The only difference is that for ia64 the 'expected > minimum stack footprint' is larger, due to the switch_stack.
the patch below unrolls the prefetch_range() loop manually, for up to 5 cachelines prefetched. This patch, ontop of the 4 previous patches, should generate similar code to the assembly code in your original patch. The full patch-series is:
patches/prefetch-next.patch patches/prefetch-mm.patch patches/prefetch-kstack-size.patch patches/prefetch-unroll.patch
Ingo
--------- unroll prefetch_range() loops manually.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
include/linux/prefetch.h | 31 +++++++++++++++++++++++++++++-- 1 files changed, 29 insertions(+), 2 deletions(-)
Index: linux/include/linux/prefetch.h =================================================================== --- linux.orig/include/linux/prefetch.h +++ linux/include/linux/prefetch.h @@ -58,11 +58,38 @@ static inline void prefetchw(const void static inline void prefetch_range(void *addr, size_t len) { #ifdef ARCH_HAS_PREFETCH - char *cp; + char *cp = addr; char *end = addr + len; - for (cp = addr; cp < end; cp += PREFETCH_STRIDE) + /* + * Unroll agressively: + */ + if (len <= PREFETCH_STRIDE) prefetch(cp); + else if (len <= 2*PREFETCH_STRIDE) { + prefetch(cp); + prefetch(cp + PREFETCH_STRIDE); + } + else if (len <= 3*PREFETCH_STRIDE) { + prefetch(cp); + prefetch(cp + PREFETCH_STRIDE); + prefetch(cp + 2*PREFETCH_STRIDE); + } + else if (len <= 4*PREFETCH_STRIDE) { + prefetch(cp); + prefetch(cp + PREFETCH_STRIDE); + prefetch(cp + 2*PREFETCH_STRIDE); + prefetch(cp + 3*PREFETCH_STRIDE); + } + else if (len <= 5*PREFETCH_STRIDE) { + prefetch(cp); + prefetch(cp + PREFETCH_STRIDE); + prefetch(cp + 2*PREFETCH_STRIDE); + prefetch(cp + 3*PREFETCH_STRIDE); + prefetch(cp + 4*PREFETCH_STRIDE); + } else + for (; cp < end; cp += PREFETCH_STRIDE) + prefetch(cp); #endif } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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