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    SubjectRe: [RFC] [PATCH] cache pollution aware __copy_from_user_ll()
    On Tue, 2005-08-16 at 12:30 +0900, Hiro Yoshioka wrote:

    > The following example shows the L3 cache miss is reduced from 37410 to 107.

    most impressive; it seems the approach to do this selectively is paying
    off very well!

    The only comment/question I have is about the use of prefetchnta; that
    might have cache-evicting properties as well (eg evict the cache of the
    original of the copy, eg the userspace memory). Is that really the right
    In addition, my measurements show that removing the prefetch from the
    main copy loop is a gain because the modern cpus have an autoprefetcher
    already in the hardware.

    "1: prefetchnta (%0)\n" /* This set is 28 bytes */
    + " prefetchnta 64(%0)\n"
    + " prefetchnta 128(%0)\n"
    + " prefetchnta 192(%0)\n"
    + " prefetchnta 256(%0)\n"
    + "2: \n"
    + ".section .fixup, \"ax\"\n"
    + "3: movw $0x1AEB, 1b\n" /* jmp on 26 bytes */
    + " jmp 2b\n"
    + ".previous\n"

    oh and prefetch(nta) is a non-faulting instruction so no need for the
    fixup handling...

    But overall this is starting to look really interesting!

    Arjan van de Ven

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      Last update: 2005-08-16 07:52    [W:0.020 / U:2.148 seconds]
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