Re: [Xen-users] 47s clock skew in domUs every so often, Debian squeeze packaged hypervisor 4.0.1-2

[Steve Allison <xen-users@xxxxxxxxxxxxxxxxxx>]

On 20/09/2011 22:02, Andy Smith wrote:
> Hi,
>
> Ever since upgrading a particular machine from Debian lenny with Xen
> 3.3.x to Debian squeeze with xen-hypervisor-4.0-amd64 4.0.1-2 back
> in June, it's been inflicting an intermittent 47s clock skew on
> multiple domUs.
>
> All the domUs run ntpd, but only one of them has an ntpd which seems
> to detect it. Example:
>
> Sep 20 16:11:39 test0 ntpd[1802]: time reset -46.869813 s
> Sep  6 12:58:41 test0 ntpd[1742]: time reset -46.869301 s
> Jul 27 11:19:35 test0 ntpd[1742]: time reset -46.869786 s
> Jun 29 19:05:10 test0 ntpd[1708]: time reset -46.868480 s
>
> Another one runs heartbeat and it similarly gets upset:
>
> Sep 20 15:54:56 foo2 heartbeat: [1407]: WARN: Late heartbeat: Node foo2: 
> interval 47000 ms
> Sep  6 12:43:02 foo2 heartbeat: [1407]: WARN: Late heartbeat: Node foo2: 
> interval 47590 ms
> (logs go back no further; I expect same happened on matching dates)
>
> Its ntpd doesn't seem to complain, though.
>
> There are some customer domUs on this host running various versions
> of Debian and CentOS (both 2.6.18 backported Xen kernels and 2.6.36+
> pvops), on which dovecot sees the time go backwards and kills
> itself, but I don't have direct access to these domUs so can't
> report much other than that.
>
> There are other domUs which don't complain but this could be due to
> them having no software which cares; I have to investigate more to
> see if something is actually happening on them.
>
> Has anyone ever seen this before? I'm thinking this is a bug in Xen
> because it never happened in Xen 3.x, has only happened since
> upgrade, and the way it happens on the same day in multiple domUs
> (of different Linux distributions) suggest dom0 or hypervisor to me.
> I also have other hosts of Xen 4.x where this doesn't happen.
>
> dom0 is a Supermicro X7DCL-i, Xeon 5410 running amd64 Debian squeeze
> and the distribution Xen packages.
>
> Some info on the various hosts involved:
>
>         Distribution    Kernel
> ------------------------------------------
> dom0   Debian squeeze  2.6.32-5-xen-amd64
> foo2   Debian squeeze  2.6.32-5-686-bigmem
> test0  Debian lenny    2.6.26-2-686-bigmem
> bar0   Debian squeeze  2.6.32-5-686-bigmem
>
>         Current      Available
>         clocksource  clocksources
> -----------------------------------
> dom0   xen          xen
> foo2   tsc          xen tsc
> test0  xen          xen tsc jiffies
> bar0   xen          xen tsc
>
> Any ideas?
>
> Cheers,
> Andy
>
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> http://lists.xensource.com/xen-users
Add this to /etc/default/grub

GRUB_CMDLINE_XEN_DEFAULT="clocksource=pit"

and then update-grub

This seems to make the clock more stable.  It still looses some time but 
its not as bad and the domU's dont jerk back to normal.
--
May the ping be with you ..


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