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    SubjectRe: lmbench lat_mmap slowdown with CONFIG_PARAVIRT
    Ingo Molnar wrote:
    > Ouch, that looks unacceptably expensive. All the major distros turn
    > CONFIG_PARAVIRT on. paravirt_ops was introduced in x86 with the express
    > promise to have no measurable runtime overhead.
    > ( And i suspect the real life mmap cost is probably even more expensive,
    > as on a Barcelona all of lmbench fits into the cache hence we dont see
    > any real $cache overhead. )
    > Jeremy, any ideas where this slowdown comes from and how it could be
    > fixed?

    I just posted a couple of patches to pick some low-hanging fruit. It
    turns out that we don't need to do any pvops calls to do pte flag
    manipulations. I'd be interested to see how much of a difference it
    makes (it reduces the static code size by a few k).


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      Last update: 2009-01-22 23:29    [W:0.021 / U:3.724 seconds]
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