[Xen-users] annoying 2 - 3 second lag every few minutes in Windows XP VM on Debian 6 Squeeze

[Iordan Iordanov <iordan@xxxxxxxxxxxxxxx>]

Hi,

I don't know if this is a known issue, but I couldn't find any 
references to it online, so I figured I'd start a topic here.
I am running Debian 6 (Squeeze), and have the standard Debian 6 Xen 
kernel and all the Xen support tools and packages that come from 
Squeeze. I've created a Xen VM on the local disk:
- dd if=/dev/zero of=somefile bs=1024k count=4000 to create the disk
- Installed Windows XP sp3 from an ISO file (standard installation with 
no extras).
After booting into Windows, without any updates or anything running in 
windows, I am observing a 2 - 3 second lag or freeze or whatever you 
want to call it every few minutes. This happens no matter whether I am 
running a "local console", or connecting via VNC to the virtual machine. 
During the freeze, I've got ssh shells and lots of stuff open on the 
server, and everything is running, so it's not the connection. Also, the 
machine is not on a remote server, so it's not NFS or something like that.
While running top, I observe that during the freeze, all of the 
Xen-related processes drop off the list (i.e. do not take up any 
CPU-time). There are no tell-tale dmesg messages. Here are some details 
of the system:
Supermicro H8DGU-F motherboard, 2x Magny-cours CPU with 12 cores each, 
64GB of RAM. uname -a reports:
Linux vsrv1 2.6.32-5-xen-amd64 #1 SMP Thu May 19 01:16:47 UTC 2011 
x86_64 GNU/Linux
The reason I am certain this is a Xen issue, is that running the exact 
same VM image with qemu-kvm produces no such effect.
Many thanks for any input and/or workarounds!

Iordan Iordanov

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