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    SubjectRe: [RFC PATCH 0/3] generic hypercall support
    Anthony Liguori wrote:
    >
    > And we're now getting close to the point where the difference is
    > virtually meaningless.
    >
    > At .14us, in order to see 1% CPU overhead added from PIO vs HC, you
    > need 71429 exits.
    >

    If I read things correctly, you want the difference between PIO and
    PIOoHC, which is 210ns. But your point stands, 50,000 exits/sec will
    add 1% cpu overhead.

    >
    > The non-x86 architecture argument isn't valid because other
    > architectures either 1) don't use PCI at all (s390) and are already
    > using hypercalls 2) use PCI, but do not have a dedicated hypercall
    > instruction (PPC emb) or 3) have PIO (ia64).

    ia64 uses mmio to emulate pio, so the cost may be different. I agree on
    x86 it's almost negligible.

    --
    I have a truly marvellous patch that fixes the bug which this
    signature is too narrow to contain.



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