Intel® 64 and IA-32 Architectures Optimization Reference Manual

USING PERFORMANCE MONITORING EVENTSFigure B-2. Performance Events Drill-Down and Software Tuning Feedback LoopTypically, the logic in performance monitoring hardware measures microarchitecturalconditions that varies across different counting domains, ranging from cycles, microops,address references, instances, etc. The drill-down methodology attempts toprovide an intuitive, cycle-based view across different phases by making suitableapproximations that are described below:• Total cycle measurement — This is the start to finish view of total number ofcycle to complete the workload of interest. In typical performance tuningsituations, the metric Total_cycles can be measured by the eventCPU_CLK_UNHALTED.CORE. See Appendix A, “Performance Monitoring Events,”of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3B).• Cycle composition at issue port — The reservation station (RS) dispatchesmicro-ops for execution so that the program can make forward progress. Hencethe metric Total_cycles can be decomposed as consisting of two exclusivecomponents: Cycles_not_issuing_uops representing cycles that the RS is notB-46