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

[Jeremy Fitzhardinge <jeremy@goop.org>]

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).

     J