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Re: [Xen-users] Xen system hang or freeze


You and Nick both see this problem on a system with eight cores.
You have 4 domUs, Nick has 3 domUs.

I think a reasonable hypothesis is that this is some kind of resource starvation/livelock/deadlock scenario. Some questions that might help see how similar your scenario and Nick's are:

1. How many vcpus does each of your domUs have?
2. Do you define pinning, cap or weight for your domUs?
3. Does sar on the guests show a high %steal before the problem occurred ? 4. Do you limit the number of vcpus that Dom0 has? If not, I would suggest that you try this an dsee if the problem occurs when you know that there should be free vcpus for each of your domUs.


Do you limit your Dom0
On May 5, 2009, at 2:42 AM, Martin Fernau wrote:


did you find out anything helpful about this problem?
I just had this freeze this morning again. Server freezed and no guests working any more. After 5 weeks of normal running. It seems that this is my
intervall of this problem.

I really appreciated anything helpful about this! I'm totally stuck with this


Am Freitag, 24. April 2009 schrieb Nick Anderson:
On Thu, Apr 23, 2009 at 10:01:02PM -0400, Peter Booth wrote:
When you got the "soft lockup" errors were they always with CPU0?

Yes I believe so. But since I updated to the latest debian patched
kernel I havent seen that soft lockup error.

Do you have any nesting in your LVM definitions?


Is dom0 making use of LVM?

No it is not.

Does the host have a wireless card?


What graphics card does it have?

Just the onboard graphics 01:05.0 VGA compatible controller: ATI
Technologies Inc ES1000 (rev 02)

There is a Xen 2.6.18 kernel bug that might be related to what you see,
as well as a patch:

Yes I think that patch is in the latest kernel update which made the
soft lockup messages go away. Odly everyone else that noted the soft
lockup errors only noted them as an annoyance. I don't recall ever
seeing anyone link the messages with any actual undesirable behavior
outside of the msgs themselves.

I appreciate that this freezing occurs when the system is quiet, but it seems as if the hypervisor CPU scheduler might play some part in this, such that the guest vcpus don't get scheduled on a pcpu. If it were me I
would try limiting dom0 to four vcpus - not as a long-term
configuration, but to see whether the problem recurred when we know that
each domU should have an available CPU.

I was considering that. I also thought it interesting that each of the
domUs are running on vcpu0. I figured they would automatically
distribute to a free vcpu.

Mit freundlichem Gruß,
Martin Fernau

CPS Entwicklungsgesellschaft für EDV-Lösungen mbH
Gartenstraße 42 - 37269 Eschwege

Telefon (0 56 51) 95 99-0
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eMail m.fernau@xxxxxxxxxx
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