Can PDES scale in environments with heterogeneous delays?

The performance and scalability of Parallel Discrete Event Simulation (PDES) is often limited by communication latencies and overheads. The emergence of multi-core processors and their expected evolution into many-cores offers the promise of low latency communication and tight memory integration between cores; these properties should significantly improve the performance of PDES in such environments. However, on clusters of multi-cores (CMs), the latency and processing overheads incurred when communicating between different machines (nodes) far outweigh those between cores on the same chip, especially when commodity networking fabrics and communication software are used. It is unclear if there is any benefit to the low latency among cores on the same node given that communication links across nodes are significantly worse. In this study, we examine the performance of a multi-threaded implementation of PDES on CMs. We demonstrate that the inter-node communication costs impose a substantial bottleneck on PDES and demonstrate that without optimizations addressing these long latencies, multi-threaded PDES does not significantly outperform the multiprocess version despite direct communication through shared memory on the individual nodes. We then propose three optimizations: message consolidation and routing, infrequent polling and latency-sensitive model partitioning. We show that with these optimizations in place, threaded implementation of PDES significantly outperforms process-based implementation even on CMs.