Time Warp Parallel Discrete Event Research Articles

Dynamic Cancellation: Selecting Time Warp Cancellation Strategies at Runtime

The performance of Time Warp parallel discrete event simulators can be affected by the cancellation strategy used to send anti-messages. Under aggressive cancellation, antimessage generation occurs immediately after a straggler message is detected. In contrast, lazy cancellation delays the sending of anti-messages until forward processing from a straggler message confirms that the premature computation did indeed generate an incorrect message. Previous studies have shown that neither approach is clearly superior to the other in all cases (even within the same application domain). Furthermore, no strategy exists to make a priori determination of the more favorable cancellation strategy. Most existing Time Warp systems merely provide a switch for the user to select the cancellation strategy employed. This paper explores the use of simulation time decision procedures to select cancellation strategies. The approach is termed Dynamic Cancellation and it assigns the capability for selecting cancellation strategies to the Logical Processes (LPs) in a Time Warp simulation. Thus, within a single parallel simulation both strategies may be employed by distinct LPs and even across the simulation lifetime of an LP. Empirical analysis using several control strategies show that dynamic cancellation always performs with the best static strategy and, in some cases, dynamic cancellation provides some nominal (5–10%) performance gain over the best static strategy.

Transparent incremental state saving in time warp parallel discrete event simulation

Many systems rely on the ability to rollback (or restore) parts of the system state to undo or recover from undesired or erroneous computations. Examples of such systems include fault tolerant systems with checkpointing, editors with undo capabilities, transaction and data base systems and optimistically synchronized parallel and distributed simulations. An essential part of such systems is the state saving mechanism. It should not only allow efficient state saving, but also support efficient state restoration in case of roll back. Furthermore, it is often a requirement that this mechanism is transparent to the user. In this paper we present a method to implement a transparent incremental state saving mechanism in an optimistically synchronized parallel discrete event simulation system based on the Time Warp mechanism. The usefulness of this approach is demonstrated by simulations of large, detailed, realistic FCA and a DCA-like cellular phone systems.