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

Peter Zijlstra
2010-04-19T10:51:19Z

On Mon, 2010-04-19 at 13:49 +0300, Avi Kivity wrote:
> On 04/19/2010 01:46 PM, Peter Zijlstra wrote:
> > 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.
> >
> >
>
> Sockets and boards too? (IOW, how reliable is TSC_RELIABLE)?

Not sure, IIRC we clear that when the TSC sync test fails, eg when we
mark the tsc clocksource unusable.