RE: [Xen-devel] RE: rdtsc: correctness vs performance on Xen (and KVM?)

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> There's still a race there

Good point.  Essentially we need to ensure that
{{rdtsc and the pvclock struct values for PCPU-X}}
are obtained atomically and there's no way to guarantee
that (at least without incurring overhead that's likely
to exceed just emulating rdtsc to begin with).
 
> > I'm clueless about GDTs and the LSL instrution so would
> > need some help prototyping this.
> >   
> 
> It's what vsyscall already uses.  Your scheme is precisely 
> analogous to
> what's already there.

(...except if it can be done entirely in the app with no
OS dependencies)

Won't pvclock+vsyscall have the same race?

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