[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] Time skew on HP DL785 (and possibly other boxes)
> > The goal for Xen timekeeping is to ensure that if a guest > > could somehow magically read any of its virtual clocks > > (tsc, pit, hpet, pmtimer, ??) on all its virtual processors > > simultaneously, the values read must always obey this > > "virtual clock law": > > We can do this for all except TSC for HVM guests because I understand that this is true IFF Xen system time itself obeys the virtual clock law. I am concerned that maybe it cannot on machines such as this. If not, NO HVM guest clock will obey the law, correct? > Everything else builds on Xen system time, and Xen system > time should just > require each CPU's TSC to be individually stable. > ...I think the benefit of your patch was in > sync'ing system > time across all CPUs at the same time, which significantly > reduced maximum divergence. The problem was, in our testing on this DL785, the maximum divergence was not reduced enough! This was tested with xen-unstable (not sure what c/s). > One concern I have however, is Intel's > X86_FEATURE_CONSTANT_TSC logic. It's possible that this (or some other problem) has resulted in the divergenece on the DL785. So more testing is in order. Dan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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