[TriLUG] Xen HVM guest has severe clock drift
Joseph S. Tate
dragonstrider at gmail.com
Thu Mar 10 10:43:00 EST 2011
Ugh, who's it with so we know to stay far away? Xen does not have an
independent time source, it's clock is controlled by the hypervisor.
NTP can't keep up because a xen guest cannot set the clock.
The only decent VPS I've had is with slicehost/rackspace. All the
other ones have sucked in one way or another, even Linode.
On Thu, Mar 10, 2011 at 9:02 AM, Warren Myers <volcimaster at gmail.com> wrote:
> 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
> 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
>> [ 0.396000] * this clock source is slow. Consider trying other clock
>> [ 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
>> $ cat /sys/devices/system/clocksource/clocksource0/current_clocksource
>> 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
>> This message was sent to: Warren <volcimaster at gmail.com>
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> Warren Myers
> This message was sent to: Joseph Tate <dragonstrider at gmail.com>
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