Re: [Xen-users] Time diferrence between dom0 and domU

[Jordi Espasa Clofent <jespasac@xxxxxxxxxxxx>]

First of all, thanks for your response Bartosz. ;)

> I'm facing similar problems. My ocnfiguration: XEN 3.4.1 + kernel from 
> http://git.kernel.org/?p=linux/kernel/git/jeremy/xen.git;a=shortlog;h=xen/master
I've suffered this trouble since 3.0.x version. What a pity!

> 1. Just afer DomU starts it's time differs from dom0 clocks: software (date) 
> and hardware (hwclock --show --utc). In my case it's ~10s. It's not caused by 
> wrong /etc/localtime. If it were, then round hours would be the difference. 
Mmmm... I think I don't understand completely what you say. Could you 
elaborate more this argument please?
> 2. DomU's clock drifts.
>
> I've made 2 things as a workaround:
>
> 1. I've installed ntpd in domU, too. I read somewhere that it sould be done as 
> a workaround, until the source of te poblem is found and fixed. With ntpd 
> running DomU's clock still drifted, but when the difference was approaching 1s 
> ntpd reseted the clock. 
Yes. I've also tried to set up a ntpd in domU (activating the 
independent_wallclock entry in /proc)
but it seems not works at all.

> 2. I've changed timer interrupt frequencies to 1000Hz in dom0 and to 100Hz in 
> domU. That was done by kernel recompilation, of course. Now, domU's clocks 
> differ from dom0 in range ~10ms when under small load or ~100ms under havy 
> load. Furthemore, the differences are steady - I do not observe leaps as It 
> was when domU and dom0 timer interrupt frequencies were equal.
So... ÂCan I suppose that the time difference ocurrs because the domUs 
are under high load?
> It's also handy to do:
>
> 3. On dom0 put into /etc/cron.hourly a script doing:
> /sbin/hwclock --systohc --utc
ÂWhat it means exactly?

> I'm going to report my problems to xen-devel and ask them to write some wiki 
> article on time keeping.
Yes, I thing is absolutely needed. As I've said before, I've experienced 
time sync problems between dom0 and domUs since 3.0.x version; and now 
you're talking about 3.4.x version. It's totally unacceptable. Keeping 
the time sync is an esencial feature.
--
I must not fear. Fear is the mind-killer. Fear is the little-death that 
brings total obliteration. I will face my fear. I will permit it to pass 
over me and through me. And when it has gone past I will turn the inner 
eye to see its path. Where the fear has gone there will be nothing. Only 
I will remain.
Bene Gesserit Litany Against Fear.

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