Thread priority method for ensuring processing fairness in simultaneous multi-threading microprocessors

Abstract

A method, apparatus, and computer program product are disclosed for ensuring processing fairness in simultaneous multi-threading (SMT) microprocessors. A clock cycle priority is assigned to a first thread and to a second thread during a standard selection state that lasts for an expected number of clock cycles by selecting the first thread to be a primary thread and the second thread to be a secondary thread. If a condition exists that requires overriding, an override state is executed by selecting the second thread to be the primary thread and the first thread to be the secondary thread. The override state is forced to be executed for an override period of time which equals the expected number of clock cycles plus a forced number of clock cycles. The forced number of clock cycles is granted to the first thread in response to the first thread again becoming the primary thread.