Monitoring VM Loads

I am using CentOS 5, and kvm virtualization.

My VM stack (about 10 v-machines) now often gets painfully slow, probably because of IO limitations. How could I find out where the load comes from?

virt-top on the host only shows the processor load. For this situation, it is not very useful.

It would be more useful to see on the host a list of VM “load averages”, because load average at least contains IO, in addition to CPU load. Is this possible?

- Jussi