On Tue, 24 Oct 2000, Pavel Machek wrote:
> Hi!
>
> > > oxymoron@waste.org said:
> > > > You can also pretty trivially keep track of an error term so that the
> > > > clock is right on average:
> > >
> > > True, but I don't want 'right on average'. I want 'not screwed with at all'.
> > > Shifting the timer tick onto the RTC will give me that.
> > >
> > > Even if we _do_ get the maths right, fudging with the frequency of the
> > > system timer is still an ugly hack.
> >
> > I personally think the system timer is already an ugly hack. HZ is
> > arbitrary, slow by modern standards, and introduces latency.
> > As the comment you quoted points out, it's also not very accurate.
> > Much better would be an agenda structure with one shot timers between
> > events and jiffies based on cycle counters. This works on modern hardware
> > and scales well for higher processor speeds.
>
> ...and breaks horribly when your CPU frequency changes... like on most
> current notebooks.
The unit of time is arbitrary. Cycle counts just happens to be convenient
on most machines and very high resolution. The important point is that
hanging tasks off a periodic low-resolution timer is not scaling with CPU
clock speeds at all and there are ways to throw it out.
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This archive was generated by hypermail 2b29 : Tue Oct 31 2000 - 21:00:14 EST