On Tue, Mar 30, 2010 at 10:08:28AM +0200, Sebastian Hetze wrote: > On Mon, Mar 29, 2010 at 11:31:13AM +0100, Athanasius wrote: > > I didn't see any such messages but I've had a recent experience with > > the time on one KVM host leaping *forwards* approx. 5 and 2.5 hours in > > two separate incidents. Eerily the exact jumps, as best I can tell from > > logs are of 17592 and 8796 seconds, give or take a second or two. If > > you look at these as nanoseconds then that's 'exactly' 2^44 and 2^43 > > nanoseconds. > > What I've done that seems to have avoided this happening again is drop > > KVM_CLOCK kernel option from the kvm guests' kernel. > > To my understanding, kvm-clock is the best and most reliable clocksource > available, so I do not think it is a good idea to disable it. > > There is a lot of bit shift operation happening with the clocksources, > so there may be a real bug hidden somewhere in the code. > Somehow ntp adjustment is involved, can this cause such huge steps? > Im my case, I actually have NTP running in the guest. However, the > statistics show a pretty stable timing here. This is one thing thing to note, I *was* running ntpd in the affected guest (and rather obviously, I still am). If there's some bad interaction between KVM_CLOCK and ntpd it needs documenting in the first instance and preferably also fixing. -- - Athanasius = Athanasius(at)miggy.org / http://www.miggy.org/ Finger athan(at)fysh.org for PGP key "And it's me who is my enemy. Me who beats me up. Me who makes the monsters. Me who strips my confidence." Paula Cole - ME -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
