Xen users - Jun 2012 - [SOLVED] Systeminterrupts and DComLaunch eat a lot of CPU in Windows 7 HVMs

Hi,

I had a problem which I could solve and want to share my solution:


Problem:

After upgrading my xen to xen-testing 23301:a9c0a89c08f2 i saw the CPU
of my Win7 HVM beeing occupied constantly bye 50-60%. This came half
from a Systeminterrupts-Process and half from the DComLaunch
svchost.exe Process and it''s Plug & Play part which I
didn''t quite
understand. Because the usual solutions (like disabling audio
enhancements) didn''t work, I figured it was something xen related.

Solution:

In short: If you have the same problem, deactivate your Xen-CD-Drive
in the Device Manager. Because Device-Manager might hang, just
right-click on the device, click deactivate, wait about 15 seconds
(the device manager is now proberbly crashed) and reboot.

Longer:
There seems to be an issue if you have either an empty loop device or
an empty physical CD-Drive (/dev/sr0) configured as your cd-drive in a
windows hvm. The empty emulated CD-Drive (btw: this includes DVD and
Bluray, too) will send massive amounts of interrupts out of nowhere to
the domU which actually produces massive workloads in systeminterrupts
and the processes responsible for plug and play. I haven''t looked into
this problem more and can''t say what is actually causing this in the
xen Code, but I''m fairly sure this is not a domU-OS problem because i
could recreate it with 5 different Win7 x64 DomUs with and without
PVOPS-Driver.