On Mon, Mar 29, 2010 at 11:31:13AM +0100, Athanasius wrote: > On Sun, Mar 28, 2010 at 01:46:35PM +0200, Sebastian Hetze wrote: > > this message appeared in the KVM guest kern.log last night: > > > > Mar 27 22:35:30 guest kernel: [260041.559462] Clocksource tsc unstable (delta = -4398046474878 ns) > > > > The guest is running a 2.6.31-20-generic-pae ubuntu kernel with > > hrtimer-tune-hrtimer_interrupt-hang-logic.patch applied. > > > > If I understand things correct, in kernel/time/clocksource.c > > clocksource_watchdog() checks all the > > /sys/devices/system/clocksource/clocksource0/available_clocksource > > every 0.5sec for an delta of more than 0.0625s. So the tsc must have > > changed more than one hour within two subsequent calls of > > clocksource_watchdog. No event in the host nor anything in the > > guest gives reasonable cause for this step. > > > > However, the number 4398046474878 is only 36226 ns away from > > 4*1024*1024*1024*1024 > > 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. -- 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
