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

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Time diferrence between dom0 and domU
From: Jordi Espasa Clofent <jespasac@xxxxxxxxxxxx>
Date: Mon, 09 Nov 2009 13:32:11 +0100
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Jordi,

Sorry for writing the above line in a hurry.

No problem.

I observe, that my domU clock differs from dom0 clock from the very beginning. Thus I think it's something wrong with xen tools that setup a new domain or the prblem is caused by hypervisor or kernel that miss some number of clock ticks during kernel boot.

IMHO this is important. Is there any related bug at "official level"?

In my combination of Xen(3.4.1)/kernel(2.6.31.5/jeremy) I have no such entry in the /proc tree or I don't know how to make independent_wallclock entry apear somewhere there. But the workaround works without writing to this entry.

Ok.

Well, it seems that hypervisor's mechanisms of sharing common clock between domains don't work. What works, is ntpd based synchronization independent of xen. Ntpd daemon works in userspace and it behaves better when the system is not fully loaded. The load I was talking about is my favorite load test: linux kernel compilation, do it again and again using at least 20 concurent jobs.

So, I understand the problem could be if you rely in ntpd (userspace) to keep up the time sync and the domU is under high load (kernel space). No?

Anyway, the solution is clear: the hypervisor must to do it correctly.

--
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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