Cloned from launchpad blueprint https://blueprints.launchpad.net/nova/+spec/granular-compute.
Hypervisor manager is the management software which controls hypervisors running on different hosts. Besides physical hosts, hypervisor manager usually has its abstract definition of the compute resource it can manage. The abstract compute resource can be the whole pool of hosts managed by a hypervisor manager, or a pool which consists of several physical hosts, or an individual physical host, or a set of isolated CPU cores and memory within one host. Every type of those compute resource can be individually manipulated for VM provisioning.
Traditionally, Nova compute is the model of a physical host. This blueprint attempts to enable Nova to manipulate the abstract compute resource via hypervisor manager. This way, every type of compute resource can become a 'host' managed by Nova. It provides a very flexible and granular way for Nova to provision and schedule the VM.
Specification URL (additional information):