Messages in this thread | | | From | Ryan Cumming <> | Subject | Re: [patch] Prefetching file_read_actor() | Date | Mon, 31 Dec 2001 12:40:19 -0800 |
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On December 31, 2001 11:47, Dave Jones wrote: > Completly puzzled right now. Moving the prefetching to copy_to_user > (and doing the tlb preload & prefetching the whole chunk to be copied > (or cachesize if smaller)) results in a performance drop instead of a win. > > My initial guess is that some of the callers of copy_to_user are > doing something that is harmed the prefetching. > (Maybe they are doing additional prefetch() calls)
Maybe syscalls that only have to move a very small chunk of data (gettimeofday(2), for instance), are hurt because of the wasted bytes they are prefetching after the intended data? Also, for sizes greater than 512, copy_to_user will call mmx_copy_user, which might call mmx_memcpy, which does prefetching already on x86 CPUs that support it.
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