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

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH][v4] PV extension of HVM(hybrid) support in Xen
From: Sheng Yang <sheng@xxxxxxxxxxxxxxx>
Date: Tue, 2 Mar 2010 13:04:17 +0800
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
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On Tuesday 02 March 2010 12:39:34 Jeremy Fitzhardinge wrote:
> 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.
Sorry, I misunderstood. HVM assume it start from 0... PV is following the 
native. We set the offset to 0, so that PV tsc is the same as native.

Yang, Sheng

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