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    SubjectRe: [PATCH] Move some variables into the "most_readonly" section??
    christoph <christoph@scalex86.org> wrote:
    >
    > On Wed, 8 Jun 2005, Andi Kleen wrote:
    >
    > > However this means __cacheline_aligned_mostly_readonly doesnt make much
    > > sense since there is no need for alignment in read only. How about
    > > replacing it with a __mostly_readonly that doesnt align and remove
    > > __cacheline_aligned_mostly_readonly?
    >
    > Hmm. No.

    Think so. If an object is in its own cacheline then it won't be pingponged
    around by writes to unrelated nearby objects.

    > The bigger cpu maps may benefit from cacheline alignment for
    > even for read access.

    A tiny bit, because the bitmaps might straddle one more cacheline than they
    strictly need to.

    > Here is a patch that introduces __mostly_readonly in
    > addition to __cacheline_aligned_mostly_readonly:

    I think readmostliness and alignment are mostly-unrelated concepts and
    should have separate tag thingies. IOW,
    __cacheline_aligned_mostly_readonly goes away and to handle things like the
    cpu maps we do:

    char foo[8] __cacheline_aligned _mostly_readonly = { whatever };


    (I shall now go away and quietly tear my hair out. Those mostly-readonly
    patches caused a mountain of grief:

    optimise-storage-of-read-mostly-variables.patch
    optimise-storage-of-read-mostly-variables-fix.patch
    optimise-storage-of-read-mostly-variables-x86_64-fix.patch
    optimise-storage-of-read-mostly-variables-x86_64-fix-fix.patch
    optimise-storage-of-read-mostly-variables-x86_64-fix-fix-fix.patch
    move-some-more-structures-into-mostly_readonly-and-readonly.patch
    kexec-x86_64-optimise-storage-of-read-mostly-variables-x86_64-fix.patch

    Once this is sorted I'll drop the lot and we start from a clean slate).
    -
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