Re: rdtsc to mili secs?

Vojtech Pavlik
2000-11-18T22:44:40Z

On Sat, Nov 18, 2000 at 09:12:31PM +0100, Pavel Machek wrote:

> > Anyway, this should be solvable by checking for clock change in the
> > timer interrupt. This way we should be able to detect when the clock
> > went weird with a 10 ms accuracy. And compensate for that. It should be
> > possible to keep a 'reasonable' clock running even through the clock
> > changes, where reasonable means constantly growing and as close to real
> > time as 10 ms difference max.
> >
> > Yes, this is not perfect, but still keep every program quite happy and
> > running.
>
> No. Udelay has just gone wrong and your old ISA xxx card just crashed
> whole system. Oops.

Yes. But can you do any better than that? Anyway, I wouldn't expect to
be able to put my old ISA cards into a recent notebook which fiddles
with the CPU speed (or STPCLK ratio).

> BTW I mailed patch to do exactly that kind of autodetection to the
> list some time ago. (I just can't find it now :-( -- search archives
> for 'TSC is slower than it should be'.

If I recall correctly, that patch didn't create a 'reasonable clock' -
it wasn't growing all the time and could skip back sometimes.

--
Vojtech Pavlik
SuSE Labs