[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Clock jumped 50 minutes in dom0 caused incorrect 2008 R2 domU time
On Wed, Oct 06, 2010 at 08:41:51AM -0700, Jeremy Fitzhardinge wrote: > On 10/06/2010 04:16 AM, Mark Adams wrote: > > Hi Xen-Devel's > > > > Please see my note below regarding a serious issue where my clock jumped > > in dom0. I'm sending this through to the devel list as I haven't managed > > to glean any clear help from xen-users and the debian bug team are > > unsure what could have caused this. > > > > Can you confirm if the kernel or xen controls the clock in dom0? I also > > understand that this could be an underlying hardware issue but I have > > another system on exactly the same hardware which hasn't had this occur. > > The kernel manages its own time, but it uses the Xen system clock as its > timebase. If the Xen system clock is unstable for some reason, then it > will affect the kernel's timekeeping. > > Nothing should be using the tsc clocksource, so I'm not sure why its > reporting any kinds of messages. No PV Xen domain can expect the raw > tsc to be stable. The message was reported in dom0, not domU. > > But the tsc is the basis for the Xen clocksource, and if the tsc is > unstable in unexpected ways then it can affect Xen timekeeping. This > can be caused by certain power management modes. > > > Any advice on how to investigate further or ensure better clock > > stability across dom0 and domU would be appreciated. > > What type of system is it? How many CPUs? What CPU vendor? It is a Tyan S7010AGM2NRF with 2 intel quad core Xeon E5620 CPU's. Thanks, Mark > > > Also is it correct behaviour for Xen to reboot an 2008 R2 HVM domU if > > the time moves this much? My guess is that the domU crashed when the > > time changed, and was thus rebooted automatically. Strangely the Windows > > 2003 server didn't get rebooted. > > I don't think there would be any direct connection between the dom0 time > jump and Windows dying, but if the CPU's tsc and/or Xen's timekeeping is > unstable, then Windows might also see a similar time jump and react badly. > > J > > > If you need any more info to help please let me know. > > > > Thanks, > > Mark > > > > On Mon, Oct 04, 2010 at 01:00:51PM +0100, Mark Adams wrote: > >> On Mon, Oct 04, 2010 at 11:01:10AM +0100, Mark Adams wrote: > >>> Hi All, > >>> > >>> Im running Xen 4.0.1-rc6 Debian squeeze with pvops 2.6.32-21 kernel. > >>> Today I noticed (when kerberos to the domain controllers stopped > >>> working..) that the clock was 50 minutes out in dom0 -- This caused the > >>> HVM windows domain controllers to have the wrong time. > >>> > >>> I'm not sure if this is a kernel issue or a xen issue, but the only > >>> thing related is I can see the following in the kernel log: > >>> > >>> Oct 2 18:50:33 havhost1 kernel: [623480.977748] Clocksource tsc unstable > >>> (delta = -2999660303788 ns) > >>> > >>> But I also see in the dmesg log that xen is using it's own clock. > >>> > >>> [ 7.676563] Switching to clocksource xen > >>> > >>> I can't identify anything else in the logs to indicate when the time > >>> might have changed. I have a few other dom0 at the same level that > >>> haven't decided to change the time. > >>> > >>> Can anyone confirm whether xen controls the time or the kernel? Also > >>> when I corrected the time in dom0 it was still wrong in HVM domU -- How > >>> long does it take for this to propogate? (I rebooted the VM's to correct > >>> it immediately). > >>> > >>> Any other pointers on how to ensure stability of clocks from dom0 to > >>> domU HVM hosts (and pv for that matter..) would be appreciated. > >> Some further info on this, It appears the HVM domU (windows server 2008) > >> unexpectedly shut down at 18:51, after the unstable clocksource error. > >> qemu-dm logs show a reset "reset requested in cpu_handle_ioreq." and > >> xend.log shows a reboot > >> > >> [2010-10-02 18:51:03 1759] INFO (XendDomainInfo:2088) Domain has shutdown: > >> name=ha-dc1 id=2 reason=reboot. > >> > >> This is like someone issuing "xm reboot domain" is it not? Is it > >> possible that xen could have issued this reboot itself due to a crash? I > >> can't see any crash logs. > >> > >> Cheers, > >> Mark > > _______________________________________________ > > Xen-devel mailing list > > Xen-devel@xxxxxxxxxxxxxxxxxxx > > http://lists.xensource.com/xen-devel > > > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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