[libvirt] Globally Reserve Resources for Host

Hi, I am interested in the capability to globally reserve resources(cpu and memory) for a KVM host. I know you can configure memory limits for each guest (http://libvirt.org/formatdomain.html#elementsMemoryTuning), but would like the ability to reserve host cpu and memory without having to actively do it by modifying each guests xml. For clarity, what I mean by "reserve resources" is that there are certain cpus and a certain amount of memory that guests will never have access to. This can be achieved using cgroups. Does anyone think this functionality would be useful? This is primarily to prevent the host from being starved when the allocation of guests have the host overcommitted/oversubscribed. Note: I think vmware has a similar functionality, but I am not sure as I don't really use vmware http://blogs.technet.com/b/virtualpfe/archive/2011/08/29/hyper-v-dynamic-... Thanks for any thoughts, Dusty