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Re: [Xen-devel] [PATCH 0 of 5] PV on HVM Xen

On Mon, 15 Mar 2010, Jeremy Fitzhardinge wrote:
> On 03/15/2010 05:28 AM, Stefano Stabellini wrote:
> > I like your pv clocksource implementation.
> > The only reason why I would defer the patch is that I don't particularly
> > like the "enable_pv" hypercall, so I would try to get away without it,
> > resetting the tsc offset automatically when enabling the VIRQ_TIMER on
> > an HVM domain.
> >    
> Ah, so the issue is that if we're using the pvclock, the host and guest 
> need to share the same tsc, so we can't deal with any kind of tsc offset?
> In that case, I'd prefer to have an explicit "set/remove tsc offset" 
> vcpu op rather than making it the implicit side-effect of anything 
> else.  In particular, since clock sources and event sources are 
> completely distinct, making tsc offset (a clock source thing) affected 
> VIRQ_TIMER (and event source thing) seems like a particularly poor idea.
> That, or make the pvclock structure the HVM vcpu sees have timing 
> parameters which already incorporate the tsc offset.  We've already 
> demonstrated that there's no need to have the time info in the real 
> shared memory between Xen and the domain (it can be updated via copy 
> when needed).
OK, you are right: having an explicit "set/remove tsc offset" is
the best solution.
Sheng, are you OK with this?

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