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    SubjectRe: Interesting pentium-memcpy results
    Chris Evans (chris@ferret.lmh.ox.ac.uk) writes:

    > I just compared 2.1.46 vs. 2.1.46+pentium memcpy patch,
    > and interestingly enough found that the UNIX byte benchmarks
    > tended to _drop_ a fair bit, with the exception of process
    > creation and execl throughput. (Note that I only ran the
    > basic 'system' tests - TCP bandwidth etc. to be determined
    > when I find the newer benchmarks)
    >
    > This is most interesting since I used to swear by the patch.
    >
    > It does however show us that there still is performance to
    > be gained. I presume the process creation test will be using
    > fork() which does a lot of memcpy'ing of various process
    > credentials in kernel space.

    I think it shows that the memcpy size test is significant.
    Perhaps the FPU is best used only when explicitly requested
    for large operations. That would mean page clearing I guess.

    big_aligned_memcpy() and big_aligned_clear() perhaps?
    For 512 bytes and up, optimized for each arch.

    There may be a conflict with the user-space version.
    With both the kernel and apps abusing the FPU for memcpy,
    the FPU must be restored too often.

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