I am transitioning from Xen to KVM, and will be using Fedora 14. I plan to use cgroups to assign priorities to VMs.
My question is as follows: If I place VMs in various cgroups, should I also put all other Domain-0 (physical host) processes in a single cgroup, which I would then assign lower priority? The analogy for Xen would be that all Dom0 processes are batch scheduled when the Dom0 "VM" is scheduled, so by placing them all in the same cgroup, I would be emulating this behavior. However, since KVM doesn't suffer from the same Dom0 IO dependencies as Xen, I could assign the Dom0 cgroup a low priority.
In other words, is there any potential performance degradation from all the background Dom0 processes, like ntpd, yum etc, competing with VMs whose resource allocations are being explicitly controlled via cgroups? What is the best practice here?