Messages in this thread | | | Date | Mon, 19 Apr 2010 08:35:45 -1000 | From | Zachary Amsden <> | Subject | Re: [PATCH 1/5] Add a global synchronization point for pvclock |
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On 04/19/2010 12:54 AM, Avi Kivity wrote: > On 04/19/2010 01:51 PM, Peter Zijlstra wrote: >> >>>> 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. > > Worrying. By the time we detect this the guest may already have > gotten confused by clocks going backwards.
Upstream, we are marking the TSC unstable preemptively when hardware which will eventually sync test is detected, so this should be fine.
Zach
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