Re: [PATCH 1/5] Add a global synchronization point for pvclock

Peter Zijlstra
2010-04-19T10:46:20Z

On Sat, 2010-04-17 at 21:48 +0300, Avi Kivity wrote:
> > After this patch is applied, I don't see a single warp in time during 5 days
> > of execution, in any of the machines I saw them before.
> >
> >
>
> Please define a cpuid bit that makes this optional. When we eventually
> enable it in the future, it will allow a wider range of guests to enjoy it.

Right, so on x86 we have:

X86_FEATURE_CONSTANT_TSC, which only states that TSC is frequency
independent, not that it doesn't stop in C states and similar fun stuff.

X86_FEATURE_TSC_RELIABLE, which IIRC should indicate the TSC is constant
and synced between cores.