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    SubjectRe: gettimeofday order of magnitude slower with pmtimer, which is default
    Quoting OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>:

    > Con Kolivas <kernel@kolivas.org> writes:
    > > The pm timer is very fast when the timer is latched and that strange loop
    > uses
    > > hardly any cpu time. The same can't be said about the unlatched timer case
    >
    > > where absurd amounts of cpu seem the norm. You have a catch 22 situation if
    >
    > > you depend on the accuracy of the pm timer only to end up wasting time
    > trying
    > > to actually use that timer.
    >
    > Actually, pmtmr not seems very fast, rather it's slow like usual I/O port.

    What I mean is that I've seen profiles of the worst (from Andi) showing up to 5%
    cpu time on some workloads! That's a heck of a lot slower than when it's
    latched.

    > is about 1us.
    >
    > And the following is test of gettimeofday(). Probably, we need a patch.
    > Umm....
    >
    > 2.6.16 (pmtmr)
    > Simple gettimeofday: 3.6532 microseconds


    > 2.6.16+patch (pmtmr)
    > Simple gettimeofday: 1.4582 microseconds

    Looks well worth it

    > 2.6.16 (tsc)
    > Simple gettimeofday: 0.4037 microseconds


    > Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

    Thanks!

    > + if (unlikely(pmtmr_need_workaround)) {

    I would not put this in an unlikely because on the machines where
    pmtmr_need_workaround is true this will always be true.

    Cheers,
    Con

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