Load-Aware Dynamic Time Synchronization in Parallel Discrete Event Simulation

Traditional Parallel Discrete Event Simulation (PDES) systems employ a monolithic approach for choosing their thread synchronization protocol. They either implement a Time Window-based conservative synchronization or an optimistic event processing capability based on the Time Warp synchronization. In this paper, we show that this binary choice is suboptimal and unnecessary, particularly in the realistic situation where the load distribution across the simulation domain changes over time. We thus propose a new PDES synchronization scheme, called Hybrid PDES, that dynamically switches between conservative and optimistic synchronization protocols based on the simulation run time characteristics. The primary objective of Hybrid PDES is to exploit the optimistic event processing as long as it is beneficial for the system performance and scalability. We implement Hybrid PDES in Python- and Lua-based Simian PDES engines and demonstrate up to 3X performance improvements on Intel Knights Landing and AMD EPYC processors based on the Phold, La-pdes and PPT-GPU simulation applications.