Two-level representative workload phase detection

A subset of a workload, which includes a total set of dynamic instructions, is identified to use as a trace. Processor unit hardware executes the entire workload in real-time using a particular dataset. The processor unit hardware includes at least one microprocessor and at least one cache. The real-time execution of the workload is monitored to obtain information about how the processor unit hardware executes the workload when the workload is executed using the particular dataset to form actual performance information. Multiple different subsets of the workload are generated. The execution of each one of the subsets by the processor unit hardware is compared with the actual performance information. A result of the comparison is used to select one of the plurality of different subsets that most closely represents the execution of the entire workload using the particular dataset to use as a trace.