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    SubjectRe: [PATCH] slub: reduce overhead of slub_debug
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    From: Christoph Lameter <cl@linux.com>
    Date: Thu, 7 Jul 2011 14:12:37 -0500 (CDT)

    > On Thu, 7 Jul 2011, Pekka Enberg wrote:
    >
    >> On Thu, 7 Jul 2011, Pekka Enberg wrote:
    >> > > Looks good to me. Christoph, David, ?
    >>
    >> On Thu, 2011-07-07 at 13:17 -0500, Christoph Lameter wrote:
    >> > The reason debug code is there is because it is useless overhead typically
    >> > not needed. There is no point in optimizing the code that is not run in
    >> > production environments unless there are gross performance issues that
    >> > make debugging difficult. A performance patch for debugging would have to
    >> > cause significant performance improvements. This patch does not do that
    >> > nor was there such an issue to be addressed in the first place.
    >>
    >> Is there something technically wrong with the patch? Quoting the patch
    >> email:
    >>
    >> (Compiling some project with different options)
    >> make -j12 make clean
    >> slub_debug disabled: 1m 27s 1.2 s
    >> slub_debug enabled: 1m 46s 7.6 s
    >> slub_debug enabled + this patch: 1m 33s 3.2 s
    >>
    >> check_bytes still shows up high, but not always at the top.
    >>
    >> That's significant enough speedup for me!
    >
    > Ok. I had a different set of numbers in mind from earlier posts.
    >
    > The benefit here comes from accessing memory in larger (word) chunks
    > instead of byte wise. This is a form of memscan() with inverse matching.
    >
    > Isnt there an asm optimized version that can do this much better (there is
    > one for memscan())? Optimizing this in core code by codeing something as
    > generic as that is not that good since the arch code can deliver better
    > performance and it seems that this is functionality that could be useful
    > elsewhere.

    You're being so unreasonable, just let the optimization in, refine it
    with follow-on patches.


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