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    SubjectRe: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable
    Andi Kleen wrote:
    > One thing I was pondering was to replace the expensive popfs with
    >
    > bt $IF,(%rsp)
    > jnc 1f
    > sti
    > 1:
    >
    > But would be mostly a P4 optimization again and I'm not 100% sure it is
    > worth it.
    >

    Worth it on 32-bit. On AMD64, probably not. On Intel 64-bit, maybe,
    but less important than in P4 days.

    This could change character completely if used at the tail of a function
    where you now have

    sti; 1: ret

    Which generates an interrupt holdoff on the ret, an unusual thing to do.

    Zach
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