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    SubjectRe: [PATCH 0/8] Intel I/O Acceleration Technology (I/OAT)
    On Sat, Mar 04, 2006 at 01:41:44PM -0800, David S. Miller (davem@davemloft.net) wrote:
    > From: Jan Engelhardt <jengelh@linux01.gwdg.de>
    > Date: Sat, 4 Mar 2006 19:46:22 +0100 (MET)
    >
    > > Does this buy the normal standard desktop user anything?
    >
    > Absolutely, it optimizes end-node performance.

    It really depends on how it is used.
    According to investigation made for kevent based FS AIO reading,
    get_user_pages() performange graph looks like sqrt() function
    with plato starting on about 64-80 pages on Xeon 2.4Ghz with 1Gb of ram,
    while memcopy() is linear, so it can be noticebly slower than
    copy_to_user() if get_user_pages() is used aggressively, so userspace
    application must reuse the same, already grabbed buffer for maximum
    performance, but Intel folks did not provide theirs usage case and any
    benchmarks as far as I know.

    --
    Evgeniy Polyakov
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