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    SubjectRe: lmbench lat_mmap slowdown with CONFIG_PARAVIRT
    On Thu, 2009-01-22 at 14:44 -0800, Jeremy Fitzhardinge wrote:

    > I did have some patches to do that at one point. If you set pgd_val =
    > paravirt_nop, then the patching machinery will completely nop out the
    > call site. The problem is that it depends on the calling convention
    > using the same regs for the first arg and return - true for 32-bit, but
    > not 64. We could fix that with identity functions which the patcher
    > recognizes and can replace with either pure nops or inline appropriate
    > register moves.

    What about removing the identity functions entirely. They are useless,
    really. All that is needed is a patch site filled with nops for Xen to
    overwrite, just stuffing the value into the proper registers. For
    64-bit, it can be a simple mov to satisfy the constraints.

    > Also, I just posted patches to get rid of all pvops calls when fetching
    > or setting flags in a pte, which I hope will help.

    Sounds like it will help.

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      Last update: 2009-01-22 23:57    [W:0.020 / U:1.108 seconds]
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