Virtualization can increase CPU utilization by allowing a large number of virtual CPUs to share a smaller number of physical CPUs. The amount of CPU time that is actually available does not change, though, so heavy activity on too many virtual CPUs can lead to contention and significant performance loss. The steal governor patch series from Shrikanth Hegde is an attempt to address that problem with a mechanism that allows virtual machines to voluntarily reduce the number of virtual CPUs they use when contention is high.