Load-Aware Dynamic Time Synchronization in Parallel Discrete Event Simulation

Abstract

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. CCS CONCEPTS• Computing methodologies → Massively parallel and highperformance simulations; Discrete-event simulation.

Multiobjective Scheduling of Hybrid Synchronization Messages

“…In [Junior et al 2020] an architecture for hybrid synchronization is presented and partially integrated into the DCB, where processes, differently from switching from conservative to optimistic mode, adapt their lookahead values and optimistic message cancellation techniques to avoid violations of time in the conservatives. More recently Hybrid PDES [Eker et al 2021] presents a hybrid synchronization system that changes the synchronization mode of the entire simulation between conservative and optimistic modes according to a message distribution estimate.This work is complementary to the hybrid synchronization work since our goal is not to propose a new architecture. We propose a scheduling policy for hybrid synchronization.…”

“…The UVT approach [Jefferson and Barnes 2017] makes processes change between conservative and optimistic methods dynamically during the simulation. Differently, Hybrid PDES [Eker et al 2021] changes the entire simulation synchronization mode. Yet, another different approach enables conservative and optimistic processes to run at the same time during the simulation [Junior et al 2020].…”