Dave:
In the Red Hat 5 Virtualization documentation it seems to strongly recommends having at least one physical cpu per VM. Since I have a quad core and I want to run the host plus 2-3 VMs, I decided give each VM one virtual cpu. Maybe I was too cautious.
In section 28.4 of the RHEL 5.4 Virtualization Guide, they state:
Virtualized CPUs are overcommitted best when each virtualized guest only has a single VCPU. The Linux scheduler is very efficient with this type of load. KVM should safely support guests with loads under 100% at a ratio of 5 VCPUs Overcommitting single VCPU virtualized guests is not an issue.
So, if you are going to overcommit CPUs, make sure each one of the guests has a single VCPU. If you want to allocate multiple VCPUs to the guests, do not overcommit the CPUs.
I hope this helps, Neil
-- Neil Aggarwal, (281)846-8957, http://UnmeteredVPS.net CentOS 5.4 VPS with unmetered bandwidth only $25/month! 7 day no risk trial, Google Checkout accepted