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    SubjectRe: [PATCH 0/6] Per-processor private data areas for i386
    Pavel Machek wrote:
    > So we have 4% slowdown...
    >

    Yes, that would be the worst-case slowdown in the hot-cache case.
    Rearranging the layout of the GDT would remove any theoretical
    cold-cache slowdown (I haven't measured if there's any impact in practice).

    > ...and 0.2% smaller kernel. I guess you should demonstrate speedup at
    > complex syscalls before wedecide it is worth it...

    That would be nice, but this patch series isn't really intended to be a
    performance improvement. That would be nice, but the main motivation is
    to make inline assembler patching for the paravirt work cleaner.

    Rusty and I have also been investigating how to use the %gs-based memory
    to implement all percpu data, rather than the few special cases this
    patch series currently covers, which will help further amortize the
    entry/exit cost.

    Rusty has also done more comprehensive benchmarks with his variant of
    this patch series, and found no statistically interesting performance
    difference. Which is pretty much what I would expect, since it doesn't
    increase cache-misses at all.

    J
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