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    SubjectRe: [PATCH] Remove implicit list prefetches for most cases
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    On Wed, 2010-09-08 at 10:59 +0200, Andi Kleen wrote:
    > From: Andi Kleen <ak@linux.intel.com>
    >
    > We've had explicit list prefetches in list_for_each and friends
    > for quite some time. According to Arjan they were originally
    > added for K7 where they were a slight win.
    >
    > It's doubtful they help very much today, especially on newer CPUs with
    > aggressive prefetching. Most list_for_eachs bodies are quite short and
    > the prefetch does not help if it doesn't happen sufficiently in advance
    > or when the data is not really cache cold.
    >
    > The feedback from CPU designers is that they don't like us using explicit
    > prefetches unless there is a very good reason (and list_for_each* alone
    > clearly isn't one)
    >
    > Also the prefetches cause the list walks to generate bad code,
    > increase the number of registers needed.

    If prefetch() is generally considered a "Bad Thing", I'm OK with just
    removing them from NetLabel; no need to rename and conditionalize. I
    put them in the netlbl_af[4,6]list_*() routines because those routines
    were modeled after the normal list routines which had prefetches and I
    just assumed someone much smarter had found them to be a win.

    --
    paul moore
    linux @ hp




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