[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] #599161: Xen debug patch for the "clock shifts by 50 minutes" bug.
On 08/11/2012 16:45, "Tim Deegan" <tim@xxxxxxx> wrote: >>> I wonder whether the overflow handling should just be removed, or made >>> conditional on a command-line parameter, or on the 32-bit platform counter >>> being at least somewhat likely to overflow before a softirq occurs -- it >>> seems lots of systems are using 14MHz HPET, and that gives us a couple of >>> minutes for the plt_overflow softirq to do its work before overflow occurs. >>> I think we would notice that outage in other ways. :) >> >> Iirc we added this for a good reason - to cover the, however >> unlikely, event of Xen running for very long without preemption. >> Presumably most of the cases got fixed meanwhile, and indeed >> a wraparound time on the order of minutes should make this >> superfluous, but as the case here shows that code did spot a >> severe anomaly (whatever that may turn out to be). > > ISTR when this code went in we were dealing with a timer that had a > period of about 4 seconds (ACPI PMTIMER?). It might well be OTT for the > HPET, but if there's something weird going on I'd like to track it down > while we have some sort of a handle on it. It must have been the PMTIMER. It's the only counter narrower than 32 bits (legacy PIT we simulate as a 32-bit counter behind the scenes). -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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