Re: [Xen-devel] Re: [PATCH][v4] PV extension of HVM(hybrid) support in Xen

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 03/01/2010 07:36 PM, Sheng Yang wrote:
> > static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
> > {
> >         u64 delta = native_read_tsc() - shadow->tsc_timestamp;
> >         return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow-
> > tsc_shift);
> > }
> >      
> tsc_timestamp take the vcpu beginning at 0, so that's the assumption.
Why would it be 0?  Xen sets tsc_timestamp to the current tsc when it 
updates the time parameters, which is whenever the vcpu is scheduled on 
a pcpu (and other times).  There's no expectation that the tsc starts 
from 0, since that won't ever be the case.
    J

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