Thread entries are stored in a memory of the system to indicate executed instruction threads. Uses of processing resources by the respective instruction threads are detected and history entries for the threads are stored in a memory of the system. Such history entries indicate whether respective processing resources have been used by respective ones of the instruction threads. The history entriesof first and second ones of the instruction threads are compared. The second instruction thread is selected for executing if the comparing indicates history of processing resources used by the first thread has a certain difference relative to history of processing resources used by the second thread.