[TriLUG] Xen HVM guest has severe clock drift

[Warren Myers]

Sounds like the host is severely overloaded. I personally haven't seen this
kind of clock drift since the early days of VMware Server trying to run too
many guests at once on a laptop, or a light physical machine trying to run
ESX with some heavy-lift VMs

-WMM

On Thu, Mar 10, 2011 at 07:06, Igor Partola <igor at igorpartola.com> wrote:

> Good morning.
>
> I recently rented a VPS from a provider that runs on a Xen HVM
> platform. I am running Ubuntu 10.10 i686 (2.6.35-22-generic-pae) on
> it. I continuously run ntpd, but the clock drifts by as much as 30
> seconds in 5 minutes and NTP cannot keep up. Has anyone experienced
> this? What could be the root cause of this problem?
>
> Here are some details:
>
> $ dmesg | grep clock
> [    0.160000] Measured 347 cycles TSC warp between CPUs, turning off TSC
> clock.
> [    0.396000] * this clock source is slow. Consider trying other clock
> sources
> [    0.550448] Switching to clocksource acpi_pm
> [    0.653135] rtc_cmos 00:05: setting system clock to 2011-03-09
> 02:45:40 UTC (1299638740)
>
> $ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
> acpi_pm
>
> $ cat /sys/devices/system/clocksource/clocksource0/current_clocksource
> acpi_pm
>
> So far I've tried the following things:
>
> 1. I tried disabling ACPI.
> 2. I replaced openntpd with ntp and added "tinker panic 0" to the top
> of my /etc/ntp.conf file
> 3. I read up about xen.independent_wallclock flag, which from what I
> can tell applies only to Xen PV.
> 4. Contacted the hosting provider who had little useful advice, aside
> from "you should install an ntp deamon."
>
> What could be the root cause of this problem? Is there any sort of
> remedy aside from just running an ntp daemon and losing lots of clock
> time?
> --
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-- 
Warren Myers
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