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



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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