On-line Configuration of a Time Warp Parallel Discrete Event Simulator

In Time Warp simulations, the overheads associated with rollbacks, state-saving and the communication induced by rollbacks are the chief contributors to the cost of the simulation; thus, these aspects of the simulation have been primary targets for optimizations. Unfortunately, the behavior of the Time Warp simulation is highly dynamic and greatly influenced by the application being simulated. Thus, the suggested optimizations are only effective for certain intervals of the simulation. This paper argues that the performance of Time Warp simulators benefits from a dynamic on-line decision process that selects and configures the sub-algorithms implementing the different aspects of the simulator to best match the current behavior of the simulation. In particular, we study control strategies to dynamically: (i) adjust the checkpointing (or state-saving) interval (ii) select the cancellation strategy (lazy or aggressive), and (iii) determine the policy for aggregating the application messages (an optimization that significantly improves the performance in message passing environments). The strategies have been implemented in the WARPED Time Warp simulation kernel and the performance obtained via the dynamically controlled optimizations is shown to surpass that of their best performing static counterparts.