Resources of a partitionable computer system are partitioned into: (i) a first partition for first jobs, the first jobs being at least one of small and short running; and (ii) a second partition for second jobs, the second jobs being at least one of large and long running. The computer system is run as partitioned in the partitioning step and the partitioning is periodically re-evaluated against at least one threshold for at least one of the partitions. If the periodic re-evaluation suggests that one of the first and second partitions is underutilized, the resources of the partitionable computer system are dynamically re-partitioned to reassign at least some of the resources of the partitionable computer system from the underutilized one of the first and second partitions to another one of the first and second partitions.