Modeling instruction-level parallelism for WCET evaluation

The estimation of the Worst-Case Execution Time of hard real-time applications becomes very hard as more and more complex processors are used in realtime systems. In modern architectures, estimating the execution time of a single basic block is not trivial due to possible timing anomalies linked to out-of-order execution. The influence of preceding basic blocks on the pipeline state also has to be accounted for. Recently, graphs have been used to model the execution of a block on a dynamically-scheduled pipelined processor [11]. In this paper we extend this model to express instruction-level parallelism so that superscalar processors with multiple functional units can be analyzed. Simulation results show how this extended model estimates WCETs tightly even when a realistic processor is considered. They also give an insight into the complexity of the model in terms of analysis time.