Re: [Xen-users] Issues migrating to xen 4.1

[Sylvain CHEVALIER <sylvain.chevalier@xxxxxxxxx>]

Many thanks Pasi and Claudiu for helping and sharing.

I am sorry for not giving much more details about our experiences with
dom0 hanging, but I don't want to touch our server right now as it is
running fine (except for qemu-dm memory leak) and people are using it.
I hope to set up another server this week and experiment with it.
These issues were similar to what Claudu described, but again, after
applying the fixes I described, it has been working fine, and we did
not have to revert it to 4.0.

I think we had terminal issues, with any command run locally or
remotely in dom0 giving an 'input/output' error message), and we could
not establish any other connection to it.

We are using the latest kernel on gentoo: 2.6.34-xen-r4 and had
similar issues with the previous one (2.6.34-xen-r3).

Thanks,

Sylvain

On Mon, Apr 11, 2011 at 3:30 AM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
> On Sun, Apr 10, 2011 at 12:56:05PM +0800, Sylvain CHEVALIER wrote:
>> Hi,
>>
>> We just migrated xen on gentoo on amd64 from 4.0 to 4.1 and
>> encountered a few issues that were not documented. Here is how we
>> solved them and what issues are remaining:
>>
>> 1. Our config files were referring to the LVM devices like
>> /dev/vg/domU-root with disk = [ 'phy:vg/domU-root,sda1,w' ]. This does
>> not work anymore, we have to include '/dev/': disk = [
>> 'phy:/dev/vg/domU-root,sda1,w' ].
>>
>
> Hello,
>
> I replied this 1. in another email.
>
>> 2. We were using bridges to map the 4 ethernet cards to virtual
>> machines so that virtual machines could have their own IP addresses.
>> In xen 4.1, it is recommended to configure bridges by ourselves and
>> not use xend although xend would still work. We could not get the
>> bridges to work and went on using xend. However, the network-bridge
>> script now includes a test: if a bridge already exist, then it would
>> do nothing. The problem with that is that our wrapper script for
>> network-bridge would only create the first bridge. So we had to
>> comment out the test in network-bridge, and it would work. Did anybody
>> successfully create bridges on gentoo?
>> Meanwhile, we found that if a domU is started and tries to access a
>> bridge that does not exist, dom0 would stop working. Shall it be a
>> bug?
>>
>
> What do you mean dom0 would stop working? Network dies?
> Does it work from the console?
>
> And yes, it's recommended to configure networking using the distro
> network scripts, see here for examples: 
> http://wiki.xen.org/xenwiki/HostConfiguration/Networking
>
>
>> 3. I believe we have memory issues when running a windows domU. We use
>> to allocate 512MB to domU and found that qemu would quickly use most
>> of it and after a while, dom0 would stop working. Now we allocate 4GB,
>> made sure there is no ballooning and it appears to work fine. Memory
>> leaks by qemu are widely reported but I wonder why we did not have
>> such issues before xen 4.1 update.
>>
>
> Again what do you mean with dom0 would stop working? dom0 kernel crash? 
> hypervisor crash?
> And did you mean qemu-dm process in dom0 is leaking memory?
>
>> 4. We might also have issues with CPUs. dom0 and all domU were
>> authorized to use all CPUs, and we saw the whole system freezing often
>> and quickly when mounting in charge after the 4.1 update. After we
>> spinned one CPU to dom0 we haven't seen this issue. Would this be a
>> bug?
>>
>
> This definitely sounds like a bug.
>
> Please set up a serial console and capture the error/crash messages:
> http://wiki.xensource.com/xenwiki/XenSerialConsole
>
> Also: what dom0 kernel version are you using?
>
>> Any hint or help on finding better solutions would be appreciated
>>
>
> -- Pasi
>
>

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