Aggressiveness / Risk Effects Based Scheduling in Time Warp

The Time Warp synchronization protocol for parallel discrete event simulation is characterized by aggressiveness and risk. The former property refers to greediness in the execution of unsafe events. The latter one refers to greediness in the notification of new events produced by aggressive event execution. Both these properties are potential sources for rollback occurrence/spreading. In this paper we present a scheduling algorithm for the selection of the next LP to be run on a processor which tends to keep low the joint impact of these two properties on the experienced amount of rollback. Reduction of negative effects of aggressiveness and risk is achieved by giving higher priority to the LPs whose next event has low probability to be undone due to rollback and has low fan-out that is, notifies few new events. Our algorithm differs from most previous solutions in that they miss a direct control on the effects due to risk. These solutions could originate poor performance for applications with high variance of the number of new events notified which is an indicator of the risk associated with event execution.