Assigning work, such as data packets, from a plurality of sources, such as data queues in a network processing device, to a plurality of sinks, such as processor threads in the network processing device is provided. In a given processing period, a source is selected in a manner that maintains fairness in the selection process. A corresponding sink is selected for the selected source based on processing efficiency. If, due to assignment constraints, no sink is available for the selected source, the selected source is retained for selection in the next scheduling period, to maintain fairness. In this case, to optimize efficiency, a most efficient currently available sink is identified and a source for providing work to that sink is selected.