RE: [Xen-devel] Re: time drift on dom0

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> > I've been using Xen exclusively on one of my machines for the past
> > couple of weeks and I've also noticed a time drift.  I've noticed it
> > more as minutes over the course of a week.  I thought it was just my
> > hardware dying...
> >
> > I've seen this on 2.0.2 with 2.6.9 and 2.0.3 with 2.6.10.
> 
> It's probably losing some timer interrupts. The lost tick handling
> in Linux is not very clever and results in drifting time.

The arch/xen patches to Linux effectively do away with the need for a
periodic ticker, so it's not a lost interrupt issue.

If you run NTP in dom0 the problem should go away for all domains.

Free-running from the PIT timer is typically only accurate to about
100ppm, which is about a minute a week. However, there are a couple of
things we could do to reduce some of the systematic error in setting the
PIT frequency, but this is well under 10ppm as I recall.

Ian


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