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RE: [Xen-devel] rdtscP and xen (and maybe the app-tsc answer I've been looking for)

> > Why do you need to distinguish between the two emulated 
> rdtscp cases? 
> > Special-casing a version of '0' is awkward because it would arise
> > naturally from version wraparound (after 2^31 time 
> parameter updates,
> > but still).
> You're right, I don't need to differentiate between
> the two emulated cases.  I was trying to overload
> an extra piece of information that I really don't
> need to overload.
> However, I do need one special case to indicate
> emulation vs non-emulation, so wraparound is
> still a problem.
> Fortunately, wraparound should only occur impossibly
> rarely (see below), probably less frequently than
> TSC wraparound.

I realized later that since Xen controls the values
placed in TSC_AUX, it can easily skip any special-cased
values.  Then wraparound is not a problem as long as
the app tests for "version number is different" rather
than "version number is greater."

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