[lkml]   [2010]   [Sep]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [PATCH] Remove implicit list prefetches for most cases
    On Wed, 2010-09-08 at 10:59 +0200, Andi Kleen wrote:
    > From: Andi Kleen <>
    > 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

     \ /
      Last update: 2010-09-08 14:35    [W:0.026 / U:4.764 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site