In mainframe computer system, workload tasks are accomplished using a logically partitioned data processing system, where the partitioned data processing system is divided into multiple logical partitions. In a system and method managing such a computer system, each running workload tasks that can be classified based on time criticality, and groups of logical partitions can be freely defined. Processing capacity limits for the logical partitions in a group of logical partitions based upon defined processing capacity thresholds and upon an iterative determination of how much capacity is needed for time critical workload tasks. Workload can be balanced between logical partitions within a group, to prevent surplus processing capacity being used to run not time critical workload on one logical partition when another logical partition running only time critical workload tasks faces processing deficit.