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SubjectRe: [RFC patch] Use IPI_shortcut for lapic timer broadcast
On Mon, 29 Jun 2009 16:43:16 +0800
Luming Yu <luming.yu@gmail.com> wrote:

> > Even a Pentium-5 100 MHz dual box was able to do cross-CPU IPIs
> > within 10-20 microseconds more than a decade ago - so 50-100 usecs
> > latency on a modern platform is totally out of this planet and will
> > hurt Linux performance big time. And the worst thing about it is
> > that none of the usual performance metrics will really show _why_
> > performance is tanking ...
> >
>
>
> Please note this is deep-C-state related.
> C state does add extra latency.. but I don't know how much...

C states normally only add on the "wait for" side, not on the "send"
side.

(RHEL5 is rather old, so it may have done things a bit different)

Maybe it is time for mainline to not allow a !NO_HZ config....

--
Arjan van de Ven Intel Open Source Technology Centre
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visit http://www.lesswatts.org


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