Re: cpu speed is 165mhz instead of real 650mhz

[Nico Schottelius <nico-mutt@schottelius.org>]

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Once again I am on a 147Mhz system....

george anzinger [Wed, Jul 24, 2002 at 01:13:18PM -0700]:
> Nico Schottelius wrote:
> > Joshua Uziel [Wed, Jul 24, 2002 at 03:27:09AM -0700]:
> > > * Nico Schottelius <nicos-mutt@pcsystems.de> [020724 02:03]:
> > > > This periodicly appears in my system. The Kernel seems to misdetect the
> > > > right cpu speed and then it's running only at 165mhz.
> > > > I don't really understand why this happens, there's no acpi enabled, which
> > > > caused this failure the last time.
> > >
> > > Is this a notebook computer?  Is it that you're sometimes booting it up
> > > while the system is unplugged (ie. on battery)?
> > 
> > yes,it is, but slowing down to 500 mhz is the only  available speedstep
> > option.
> > 
> > 165 or similar is not supported (afaik) by the bios/processor.
> > 
> The cpu speed is detected by comparing the TSC against the
> PIT.

I don't even now any of these both.

> The PIT is used to drive the clock.  If it is wrong by
> this much you should see time drifting like mad.

Hey, you are right! Instead of 13 o'clock it's 5 o'clock.
What todo now ? I am staying on this downclocked system, if you
need some more informations.

> If the TSC
> is wrong, you should see errors in the sub 1/HZ correction
> applied to get_time_of_day().
> You could detect this by
> looping on a get_time_of_day() call and noticing that time
> slides ahead 3/HZ seconds and then back each tick.  What
> would be happening is that the interpolation code would be
> taking the fast TSC (i.e. 500MHZ when it thought it was 165)
> and be pushing time out beyond the next tick value.  Each
> tick this would reset and be replayed.  If neither of these
> is happening, the reported value is most likely what is
> really going on.

Nice explanation. I think I understood 85 % of it :)

Nico

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