The accuracy of trace-driven simulations of multiprocessors

Abstract

In trace-driven simulation, traces generated for one set of system characteristics are used to simulate a system with different characteristics. However, the execution path of a multiprocessor workload may depend on the order of events orcurring on different processing elements. The event order, in turn, depends on system characteristics such as memory-system latencies and buffer-sizes. Trace-driven simulations of multiprocessor workloads are inaccurate unless the dependencies are eliminated from the traces. We have measured the effects of these inaccuracies by comparing trace-driven simulations to direct simulations of the same workloads. The simulators predicted identical performance only for workloads whose traces were timing-independent. Workloads that used first-come first-served scheduling and/or non-detenninistic algorithms produced timing-dependent traces, and simulation of these traces produced inaccurate performance predictions. Two types of performance metrics were particularly affected: those related to synchronization latency and those derived from relatively small numbers of events. To accurately predict such performance metrics, timing-independent traces or direct simulation should be used.