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RE: [Xen-users] Windows 2000 server VM on Xen open source CPU hog?

I ran into the same problem with Citrix's commercial product.

We saw the same thing as you, CPU usage was reported very high when the
processors were pretty much idle in windows.  When there was load in
windows, the usage in xentop dropped, as if it was the inverse of the
real usage.  This is only true with the multiproc hal.

After lots and lots of searching, I found the following KB that resolved
the issue:

Unfortunately, it was a while ago that I dealt with this issue so I
don't remember all the details, but I think it has something to do with
the way windows 2000 multiproc hal idles the cpus.  With the above
registry setting, it idle's at 0% ,as reported in xentop.

Let me know if this setting solves your problem too.

Doug Magee

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Jan Bakuwel
Sent: Wednesday, August 26, 2009 11:21 PM
To: James Harper
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Windows 2000 server VM on Xen open source CPU

Hi James,

> What does Windows 2000 report it's CPU usage at?

Below 10% when xentop consistently reports 190-199.5%.

> Does the problem appear with only a single CPU (and preferably a UP
> HAL)?

I haven't tried that yet. The server used to run on physical hardware so
anything that was on it was migrated to the VM. I noticed there are two
(?) HALs registered: ACPI Multiprocessor PC and MPS Multiprocessor PC...

> GPLPV (which doesn't work on W2K) has an option to patch windows
> < W2K3SP2 to improve performance. Backporting just that part might not
> be a huge deal, although the problem that fixes wouldn't cause 2 cpu's
> to be pegged at 100%...

I had a look at GPLPV but quickly realised Windows 2000 wasn't


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