Re: [Xen-devel] [PATCH v2 3/3] x86/viridian: Add partition time reference counter MSR support

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 04 August 2014 16:16
> To: Paul Durrant
> Cc: Ian Campbell; Ian Jackson; Stefano Stabellini; xen-devel@xxxxxxxxxxxxx;
> Keir (Xen.org)
> Subject: RE: [Xen-devel] [PATCH v2 3/3] x86/viridian: Add partition time
> reference counter MSR support
> 
> >>> On 04.08.14 at 17:11, <Paul.Durrant@xxxxxxxxxx> wrote:
> >> From: Paul Durrant
> >> I think that hvm_get_guest_time() should have the right semantics after
> all,
> >> in that it appears to be ns since a vcpu was onlined and is preserved 
> >> across
> >> save/restore.
> >
> > Actually, I'm no longer convinced about that second part. It looks like only
> > TSC is preserved across save/restore.
> 
> Indeed the saving/restoring would need to be written, similar to what
> is done for the other virtual time sources. And just like for those other
> system wide time sources, you'd have to pick a reference vCPU.
> 

Since tsc *is* saved and restored then I should be able to use 
hvm_get_guest_tsc() and convert back to ns, I think.

  Paul

> Jan


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