[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 Thu, 2012-11-08 at 12:54 +0000, Keir Fraser wrote: > On 08/11/2012 11:43, "Ian Campbell" <ijc@xxxxxxxxxxxxxx> wrote: > > >>> I'll leave this to Keir (who wrote the debugging patch) to answer but it > >>> looks to me like it should be useful! > >> > >> I'm scratching my head. plt_wrap is earlier than plt_now, which should be > >> impossible. > > > > impossible due to guarantees made by the h/w or by construction in Xen. > > That's a question, right? Yes, sorry. > By construction in Xen. > > > There appears to be a certain amount of hardware-specificness to the > > issue -- so I'm wondering if maybe there are some platforms whose tsc is > > not as monotonically increasing as it needs to be... > > plt_* timestamps are not derived from TSC at all. I see, rather it is derived from the platform_timesource which could be HPET, pmtimer, pit etc but in this case (according to the provided xm dmesg) appears to be a 14MHz HPET. So I guess s/tsc/HPET/ in my original thought... > >> plt_stamp64 oddly has low 32 bits identical to new_stamp. That > >> seems very very improbable! > > > > Does this code run on all cpus or just one? Is it always the same one? > > Always cpu0. So it's not cross cpu drift then. Ian. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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