Subject: Re: Time travel..
samuel@ibrium.se
Date: Thu Sep 20 2001 - 18:27:09 MDT
On Thu, Sep 20, 2001 at 11:59:47PM +0100, Iain Sandoe wrote:
>
> On Thu, Sep 20, 2001, Samuel wrote:
>
> > A bogus "timebase-frequency" property is serious.
> > If it is completely missing, mol will calibrate using
> > gettimeofday (this is a relatively new feature).
>
> As I understand it (from work I was doing on IRQ blocking measurement)
> *wrong* "timebase-frequency" properties were common in earlier Mac OF.
>
> AFAIK Linux does not rely on this properties (from what Ben H has told me).
>
> I can post some very simplistic user-space code to measure the TB frequency
> (close enough) on the linux side if anyone wants it (basically doing the
> same trick of calibrating it from gettimeofday).
MOL contains such a user-space measurement, but it is only
used if the timebase-frequency property is completely missing.
Perhaps one should do the gettimeofday measurement and then
compare with the OF property? I believe the OF value is
better in most cases except when it is completely wrong.
But... I would like to get a confirmation that it is
the timebase-frequency which is the culprit.
Btw, MacOS seems not to rely on the timebase-frequency either.
It performs a calibration using the VIA timer (the linux kernel
does this too).
Cheers,
/Samuel
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