1. A method for managing mainframe computer system usage comprising: implementing a management system controller on one of a plurality of logical partitions executed by a mainframe computer system; implementing a management system agent on each of the plurality of logical partitions; receiving a first performance optimization goal for performance of workload tasks in a first service class, the first service class having a first defined performance goal; assessing achievement of the first performance optimization goal based on usage information of the logical partitions by the workload tasks, the usage information received from the agents; determining a first preferred value for the first defined performance goal based on the assessing; and performing at least one of a) or b): a) requesting to change the first defined performance goal to match the first preferred value when the first preferred value is different therefrom, receiving an affirmative response to the request to change the first defined performance goal, and changing the first defined performance goal to match the first preferred value; b) automatically changing the first defined performance goal to match the first preferred value when the first preferred value is different therefrom; wherein the workload tasks are subsequently managed in the first service class according to the changed first defined performance goal; wherein the first performance optimization goal is based on at least one separate performance parameter that is not a performance parameter of the first defined performance goal; wherein the first performance optimization goal and the first defined performance goal are also based on at least one shared performance parameter; wherein assessing achievement of the first performance optimization goal includes monitoring a performance index indicative of the at least one shared performance parameter and other performance data indicative of the at least one separate performance parameter; and wherein, when the performance index indicates underachievement or overachievement outside an acceptable range, the first preferred value will represent a greater change to the first defined performance goal if the other performance data is positive rather than negative.