In addition the system administrator defines goals and importance levels for the service classes representing the application work.
Goals can be expressed as response times, a relative speed (termed velocity) or as discretionary if no specific requirement exists.
The response time describes the duration for the work requests after they entered the system and until the application signals to WLM that the execution is completed.
If this is not possible a relative speed measure – named execution velocity - is used to describe the end user expectation to the system.
The active service definition is saved on a couple data set which allows all z/OS systems of a Parallel Sysplex cluster to access and execute towards the same performance goals.
WLM is a closed control mechanism which continuously collects data about the work and system resources; compares the collected and aggregated measurements with the user definitions from the service definition and adjusts the access of the work to the system resources if the user expectations have not been achieved.
The performance index for a service class is a single number which tells whether the goal definition could be met, has been overachieved or was missed.
The access to the system processors for example is controlled by a dispatch priority which defines a relative ranking between the units of work which want to execute.
In addition WLM offers interfaces which allow load balancing components to place work requests on the best suited system in a parallel sysplex cluster.
Over time z/OS Workload Manager became the central control component for all performance related aspects in a z/OS operating system.