An apparatus and method are described for generating performance metrics of a processor. For example, one embodiment of a processor comprises: one or more simultaneous multithreading cores to simultaneously execute multiple instruction threads; a plurality of performance monitor counters, each to maintain a count of events occurring as a result of the execution of the multiple instruction threads; and a performance monitor unit to generate a plurality of performance metric values using the event counts stored in the performance monitor counters and in response to receipt of a request from software for the performance metric values.