Why is KVM Host server CPU utilization very high, when the windows guest is idle

We've had several KVM hosts up and running on Ubuntu 9.04 and 9.10 for the last 6+ months with some minor issues while initially setting up guests, but none since. Our hosts average 3 guests each and the guests do lots of different things, from multi-homed VPN servers to NAS systems with direct access to hard disks. The performance and ease of setup (once the learning curve was out of the way) has been transformative for our network.

Migration has been very easy through VNC connections over ssh via a virt-manager client; cloning has not been as smooth, as new instances have had a tendency towards flaky network errors.

The only other ongoing complaint I have is that it would be nice to have support for QEMU VLANs as an option in virt-install so we could avoid having to use the more tedious KVM commands directly. Other than that, we've been extremely happy, and most of the manangement tools are shared with Xen so I'd say use whichever one works best for you.

It's quite simple really. For homogeneous clusters and single host setups use the host option. For mixed clusters, use the lowest available CPU version, so if one host is Penryn and the other Nehalem, use Penryn on both.

If you are using RHEV or oVirt, this is already built in. VMWare have this called "EVC" and position it as a huge feature.

Getting back to performance, you definitely need virtio everywhere you can put it. And if you still hit performance bottlenecks, those can usually be addressed on a case per case basis, depending on where they occur.

[offtop]On your choice of distribution I have already commented in another thread[/offtop]