1. A computer-implemented method of managing assignment of a partition service to a virtual input/output (VIO) adapter in a data processing system comprising multiple logical partitions, the method comprising: responsive to creation of a new partition service associated with a logical partition of the data processing system, determining a partition priority number for the new partition service; summing, for each VIO adapter of at least one VIO adapter of the data processing system, partition priority numbers of partition services currently assigned to that VIO adapter; automatically determining, for a VIO adapter with a lowest sum of partition priority numbers, whether assigning the new partition service to that VIO adapter will move its sum of partition priority numbers above a predefined threshold; and automatically assigning the new partition service to a VIO adapter of the data processing system based at least in part on whether assigning the new partition service to the VIO adapter with the lowest sum of partition priority numbers will move that VIO adapter's summed partition priority number above the predefined threshold.