Re: [Xen-devel] Clock jumped 50 minutes in dom0 caused incorrect 2008 R2 domU time

[Mark Adams <mark@xxxxxxxxxxxxxxxxxx>]

This has just occurred again on another machine. Is anyone else seeing
this?

On Wed, Oct 27, 2010 at 01:29:55PM -0700, Dan Magenheimer wrote:
> > > Unfortunately these kinds of time problems can be notoriously hard to
> > > pin down and diagnose.
> > 
> > This seems to occur when one -- or possibly all -- vcpus
> > are "spinning" for an unexpectedly long period of time.  If so
> > it may be possible to synthesize some kind of long-but-non-infinite
> > deadlock in a domU kernel which might reproduce the problem.
> 
> Saw this on LKML:
> http://lkml.org/lkml/2010/10/27/366 
> 
> The solution refers to a recent git commit so is unlikely to
> be the specific cause for the problem we've seen.  But the
> analysis sounds very familiar and also corresponds to my
> observation above:  In short, SOMEthing (in the guest kernel
> or in Xen) is causing the guest to "go out to lunch" for some
> extended period of time, which confuses the watchdog timer,
> which disables TSC as a clocksource.
> 
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