Re: [Xen-users] Clock drift

[Eric Ross <eross@xxxxxxx>]

Did you look into setting your clocksource to jiffies, that seemed to
help with my live migration issues.

I struggled with time drift for months, I was running the same
configuration you were (except I didn't have any HVMs).  Then I tried
the following:

Dom0:
 independent wallclock = 1
 ntpd
 clocksource = jiffies

DomU:
 independent wallclock = 0
 clocksource = jiffies

I've been monitoring my Dom0s and DomUs with Hyperic for a few months
(specifically looking at ntp drift) and these settings produce the
closest numbers to a "bare metal" machine in my environment.

Cheers,
---------------------------------------------------------------------
Eric Ross
Linux Systems Administrator
Argonne National Laboratory
Computing and Information Systems
Phone: 630.252.2600
---------------------------------------------------------------------


Jefferson Ogata wrote:
> [Re-sending with correct source address.]
> 
> On 2008-08-16 01:59, Ray Fadaie wrote:
>> I am using Xen on a Quad Core Phenom with 8G of RAM. Everything is
>> fine except the clock! [oh god :((]
>> In Dom0 everything works just fine but in DomUs the clock (both system
>> time and the realtime clock (IRQ8) drift. I can live with the system
>> time drift (I just enforce NTP every 5 minutes) but all my
>> applications in DomUs that depend on the realtime clock (IRQ8) are
>> messed up.
>> Do you guys have any idea what could be wrong here?
>>
>> p.s. All DomUs and Dom0 are running CentOS 5 on on a M3A mother board
>> from Assus (64 bit CPU - X4).
> 
> I don't understand *why* this happens, but I've seen the same thing, as
> have many others (check Google).
> 
> I think I've got it under control now. The following works for me:
> 
> On dom0:
> - Set xen.independent_wallclock = 1 in /etc/sysctl.conf (corresponding
> to /proc/sys/xen/independent_wallclock)
> - Run ntpd.
> 
> On PVM domUs:
> - Set xen.independent_wallclock = 1 in /etc/sysctl.conf
> - Run ntpd.
> 
> On HVM domUs:
> - Disable acpi in xen config (acpi = 0).
> - Run ntpd.
> 
> The clock sometimes still jumps a bit during a live migration, but ntpd
> slews it back afterward.
> 

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