Probabilistic checkpointing in time warp parallel simulation

Abstract

In the Time Warp (TW) protocol, the system state must be checkpointed to facilitate the rollback operation. While increasing the checkpointing frequency increases the state saving cost, an infrequent scheme also escalates the coast forward effort when a large number of executed events are redone. This paper proposes a probabilistic approach to checkpointing. We derive the rollback probability, and compute the expected coast forward effort if a state is not saved. To reduce implementation overheads, the rollback probability and coast forward cost are predetermined and make available at runtime as a lookup table. Based on the derived expectation, a store vector is saved only if the expected coast forward effort is larger than the state saving cost and vice versa. Our experiments show that the cost model reduces the simulation elapsed time by close to 30% as compared to saving the system state after each event execution, and saving the system state at a predefined interval.