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

[Peter Booth <peter_booth@xxxxxxx>]

Martin,

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.
Peter


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

> Hello,
>
> 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
> problem...
>
> Martin
>
> Am Freitag, 24. April 2009 schrieb Nick Anderson:
> > On Thu, Apr 23, 2009 at 10:01:02PM -0400, Peter Booth wrote:
> > > Nick,
> > > 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?
> > No
> >
> > > Is dom0 making use of LVM?
> > No it is not.
> >
> > > Does the host have a wireless card?
> > No
> >
> > > 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:
> > > http://www.mail-archive.com/debian-kernel@xxxxxxxxxxxxxxxx/msg40893.html
> > 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
>
>
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