Re: CPU frequency shifting "problems"

Pavel Machek
2001-10-02T21:34:13Z

Hi!

> > > For example, the Intel "SpeedStep" CPU's are completely broken under
> > > Linux, and real-time will advance at different speeds in DC
> > and AC modes,
> > > because Intel actually changes the frequency of the TSC
> > _and_ they don't
> > > document how to figure out that it changed.
> >
> > The change is APM or ACPI initiated. Intel won't tell anyone anything
> > useful but Microsoft have published some of the required
> > intel confidential
> > information which helps a bit
>
> APM is a lost cause, but the correct solution for ACPI systems is to use the
> PM timer. This totally obviates the need to really care about the CPU's
> effective frequency at all. Even if you knew all the details of SpeedStep
> (and I've seen the same MS doc you have Alan and was surprised at its
> detail) you'd still be hosed if the CPU throttles...you'd be hosed in a
> *good* way because at least any delays would be longer (not shorter) than
> expected but your times would be off nonetheless.

And if it is thermal-throttledduring bogomips calibration...? [Well possible,
acpi is not active that early]

--
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details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.