[Xen-ia64-devel] RE: Xen-ia64-devel Digest, Vol 11, Issue 22

["Luck, Tony" <tony.luck@xxxxxxxxx>]

> > > during boot, linux kernel tries to synchronize itc of all processors. 
> > > However currently itc is not virtualized:
> > > (XEN) vcpu_set_itc: Setting ar.itc is currently disabled
> > >
> > > What should we do ?
> > > a) virtualize ITC
> > > b) para-virtualize ITC (ie, modifying linux kernel)
> > > c) pre-synchronize ITC
> > >
> > > I really prefer c).
> >
> >    I'm not sure I understand c).  Aren't the ITCs already
> > pre-synchronized by xen in smp_callin()?   Thanks,
> Correct, but Linux is not aware of this.
> After more thoughs, I really think this is the best solution.

What if you are running on h/w where ITC cannot be synchronized
because different cpus are driven from different clock sources?
See IA64_SAL_PLATFORM_FEATURE_ITC_DRIFT.

Solution d) might be to tell the guest that itc isn't syncronized
(even on systems where it could be).

-Tony

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