Implementing a Leading Loads Performance Predictor on Commodity Processors

Modern CPUs employ Dynamic Voltage and Frequency Scaling (DVFS) to boost performance, lower power, and improve energy efficiency. Good DVFS decisions require accurate performance predictions across frequencies. A new hardware structure for measuring leading load cycles was recently proposed and demonstrated promising performance prediction abilities in simulation. This paper proposes a method of leveraging existing hardware performance monitors to emulate a leading loads predictor. Our proposal, LL-MAB, uses existing miss status handling register occupancy information to estimate leading load cycles. We implement and validate LL-MAB on a collection of commercial AMD CPUs. Experiments demonstrate that it can accurately predict performance with an average error of 2.7% using an AMD Opteron™4386 processor over a 2.2x change in frequency. LL-MAB requires no hardware- or application-specific training, and it is more accurate and requires fewer counters than similar approaches.