Quoting OGAWA Hirofumi <[email protected]>:
> Con Kolivas <[email protected]> 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 <[email protected]>
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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