Re: [Xen-ia64-devel] SMP-guest status

[Alex Williamson <alex.williamson@xxxxxx>]

On Thu, 2006-04-20 at 15:22 +0200, Tristan Gingold wrote:
> Le Jeudi 20 Avril 2006 05:47, Alex Williamson a écrit :
> >    Is the jitter protection in the time interpolator sufficient for
> > ignoring this?  Drift is really meant to indicate the ITCs are driven
> > from different time sources so may run at slightly different clock
> > frequencies.  Seems we should only need to provide that flag to the
> > guest if the platform firmware set it.  As long as the ITCs are nearly
> > synchronized, the jitter protection in the ITC interpolator will prevent
> > time from going backwards.  This would then get rid of the change in
> > time.c.  Thanks,
> The change in time.c is just to work around a kernel bug.  Linux kernel 
> requires at least an interpolator. [Hence I think there is no platform 
> without ITC drift].

   I'm not sure I'd call it a bug.  The kernel requires some kind of
timesource for an interpolator.  AFAIK, SGI systems are the only ones
that report ITC drift and they have a platform timesource to compensate.
HPET support is another, more generic, way to do this.  If this is a
temporary workaround, I think it would be more clear to use
running_on_xen as a flag to indicate ITCs are pre-synchronized and not
report platform ITC drift via the features table.  Thanks,

        Alex

-- 
Alex Williamson                             HP Linux & Open Source Lab


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