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



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