[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 10/06/2010 09:15 AM, Mark Adams wrote: > 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. Dom0 is a normal PV domain. It just has a few more privileges than a regular 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. I forget all the magic options that can affect timekeeping (cc:d Dan, since this stuff is close to his heart). J > 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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