On Wednesday 31 March 2010 21:32:18 you wrote: > On 03/30/10 07:04, Beinicke, Thomas wrote: > > On Tuesday 30 March 2010 10:08:28 Sebastian Hetze wrote: > >> 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 > > > > I am having the same problem occasional. > > It only occurs if the VM is under heavy IO or CPU Load but I can't > > reproduce it 100%. It just never occurs on VMs that only serve a few web > > pages though. I also noticed that on a machine which has this problem > > even an ssh shell is *very* laggy so it's not just a cosmetic problem. > > > > Would removing the hrtimer from the kernel config solve it or is it > > necessary for KVM? > > > > I remember this problem has been posted her before though there wasn't > > any real conclusion or solution for it. > > Are you also running a 32-bit kernel? I have the problem on 32-bit and 64-bit clients. The host machines are all 64-bit. > Thanks, > > Zach -- 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
