[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 13:53, "Jan Beulich" <JBeulich@xxxxxxxx> wrote: >>> Is it? My understanding was that plt_stamp64 is just a software >>> extension to the more narrow HW counter, and hence the low >>> plt_mask bits would always be expected to be identical. >> >> No, plt_stamp is simply the HW counter time at which plt_stamp64 was last >> brought up to date. Hence plt_stamp64 is updated as: >> plt_stamp64 += (new_stamp - old_stamp) & plt_mask; > > I concur Well, no, you don't really. You're about to point out the flaw in my reasoning... > : Given that what old_stamp is here was new_stamp for > the last update, we should simply have > > stamp64 = s0 + (s1 - s0) + (s2 - s1) + ... > > (of course with the mask applied on each addend), which (for the > low bits) is the same as just new_stamp. Very good point. Silly me. Then the observed value of plt_stamp64 makes perfect sense. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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