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    SubjectRe: [PATCH] x86: cache pollution aware __copy_from_user_ll()

    On Sat, 24 Jun 2006, Arjan van de Ven wrote:
    > while this patch will reduce the number of cycles spent in the kernel,
    > it's just pushing the cache miss to userspace (by virtue of doing a
    > cache flush effectively)... is this really the right thing? The total
    > memory bandwidth will actually increase with this patch if you're
    > unlucky (eg if userspace decides to write to this memory eventually)....

    No. It's for copying _from_ user space, ie a "write()" system call. So
    what it does is to effectively try to use non-temporal stores to the page
    cache - since the page cache is usually not read directly afterwards (at
    least not soon enough for L1 caches to help).

    I don't generally like cache tricks either (caches tend to be better than
    humans, or at least get there fairly soon), but this one does seem very

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      Last update: 2009-11-18 23:46    [W:0.029 / U:4.396 seconds]
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