Accurate modeling of aggressive speculation in modern microprocessor architectures

Computer architects utilize cycle simulators to evaluate microprocessor chip design tradeoffs and estimate performance metrics. Traditionally, cycle simulators are either trace-driven or execution-driven. In this paper, we describe ValueSim, a software layer that is interposed between a cycle simulators and either a functional simulator or a value-enhanced trace. By writing to the ValueSim API, the cycle simulator can run in either trace-driven mode or execution-driven mode, allowing it to exploit the advantages of both approaches. The ValueSim API allows a cycle simulator to accurately model a complete range of aggressive speculative mechanisms developed by computer architects, even in the trace-driven mode. Using ValueSim, we illustrate, for three key commercial applications, the significant underestimation of off-chip bandwidth, queuing delays and cache pollution when modern speculative mechanisms are not accurately modeled, highlighting the importance of accurately modeling these mechanisms in chip multiprocessor designs.