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    SubjectRe: [patch] block layer: kmemcheck fixes
    On Fri, Feb 08, 2008 at 02:56:09PM -0800, Arjan van de Ven wrote:
    > Nick Piggin wrote:
    > >>>Maybe cpus these days have so much store bandwith that doing
    > >>>things like the above is OK, but I doubt it :-)
    > >>on modern x86 cpus the memset may even be faster if the memory isn't in
    > >>cache;
    > >>the "explicit" method ends up doing Write Allocate on the cache lines
    > >>(so read them from memory) even though they then end up being written
    > >>entirely.
    > >>With memset the CPU is told that the entire range is set to a new value,
    > >>and
    > >>the WA can be avoided for the whole-cachelines in the range.
    > >
    > >Don't you have write combining store buffers? Or is it still speculatively
    > >issuing the reads even before the whole cacheline is combined?
    > x86 memory order model doesn't allow that quite; and you need a "series" of
    > at least 64 bytes
    > without any other memory accesses in between even if it would....
    > not happening in practice.

    OK, fair enough... then it will be a very nice test to see if it
    helps. I'm sure you could have an arch specific initialisation
    function if it makes a significant difference.

     \ /
      Last update: 2008-02-09 01:01    [W:0.026 / U:14.264 seconds]
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