Hybrid Speculative Synchronisation for Parallel Discrete Event Simulation

Parallel discrete-event simulation (PDES) is a well-established family of methods to accelerate discrete-event simulations. However, the available algorithms vary substantially in the performance achievable for different models, largely preventing generic solutions applicable by modellers without expert knowledge. For instance, in Time Warp, the processing elements execute events asynchronously and speculatively with high aggressiveness, leading to frequent and costly rollbacks if misspeculations occur often. In contrast, synchronous approaches such as the new Window Racer algorithm exhibit a more cautious form of speculation. In the present paper, we combine these two fundamentally different algorithms within a single runtime environment, allowing for a choice of the best algorithm for different model segments. We describe the architecture and the algorithmic considerations to support the efficient coexistence and interaction of the algorithms without violating the correctness of the simulation. Our experiments using a synthetic benchmark and an epidemics model show that the hybrid algorithm is less sensitive to its configuration and can deliver substantially higher performance in models with varying degrees of coupling among entities compared to each algorithm on its own.