Accurate Statistical Performance Modeling and Validation of Out-of-Order Processors Using Monte Carlo Methods

Although simulation is an indispensable tool in computer architecture research and development, there is a pressing need for new modeling techniques to improve simulation speeds while maintaining accuracy and robustness. It is no longer practical to use only cycle-accurate processor simulation (the dominant simulation method) for design space and performance studies due to its extremely slow speed. To address this and other problems of cycle-accurate simulation, we propose a fast and accurate statistical modeling methodology based on Monte Carlo methods to model the performance of modern out-of-order processors. Using these statistical models, simulation and performance prediction can be achieved in seconds regardless of the modeled application's size. This paper presents the proposed methodology and its first application to model a modern out-of-order execution processor. We present a statistical model for the Opteron (Magny-Cours) processor and validate it against real hardware. Using SPEC CPU2006 and Mantevo benchmarks, the model can predict performance in terms of cycles-per-instruction within 4.79% of actual on average. We also present a novel method for generating CPI stacks which are CPI representations that quantify the contribution of individual performance components to the total CPI. To further validate these CPI stacks, we use a detailed processor simulator, build a statistical model of the simulator architecture, validate the model against the simulator, and then proceed to validate the CPI stacks predicted by our statistical model. The average CPI prediction error is 5.6%, and the average difference between the predicted and measured CPI components is 1.3% with a maximum difference of 5.4%.