RE: [Xen-devel] [PATCH] pvcpuid: mask TSC invariant bit for various circumstances

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> From: Jeremy Fitzhardinge [mailto:jeremy@xxxxxxxx]
> Sent: Thursday, October 29, 2009 4:07 PM
> To: Dan Magenheimer
> Cc: Keir Fraser; Xen-Devel (E-mail)
> Subject: Re: [Xen-devel] [PATCH] pvcpuid: mask TSC invariant bit for
> various circumstances
> 
> On 10/28/09 09:27, Dan Magenheimer wrote:
> > 3 = (a) IF processor supports rdtscp instruction:
> >        rdtsc/p is native, Xen provides TSC_AUX and pvclock info
> >     (b) IF processor doesn't support rdtscp instruction:
> >        rdtsc/p is emulated (with degenerate TSC_AUX/pvclock info)
> >   
> 
> How will this interact with operating systems which also want to use
> TSC_AUX when rdtscp is available?

Thanks for the review!

Xen does not currently expose rdtscp through pvcpuid, even when
the cpuid rdtscp bit is present.  If that should change, this
option would have to "disable" it for pvcpuid (to a PV OS)
for that guest.

Dan

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