A method, apparatus, system, and signal-bearing medium that, in an embodiment, calculate a preemption credit for a partition if a virtual processor is preempted and the partition is unable to receive an entitled capacity of physical processor cycles during a dispatch window. The preemption credit is the portion of the entitled capacity that the partition is unable to receive. As long as the partition has a remaining preemption credit, in subsequent dispatch windows, a portion of the preemption credit is allocated to the virtual processor, and the preemption credit is reduced. In this way, in an embodiment, shared processor partitions may be ensured of receiving their entitled allocation of processor cycles.