Parallel Environment for DEVS and Cell-DEVS Models

Abstract

Discrete Event System Specification (DEVS) is a sound formalism to describe generic dynamic systems in a hierarchical and modular way. Cell-DEVS is a DEVS-based formalism intended to model compleX physical systems as cell spaces. This work presents new techniques for eXecuting DEVS and Cell-DEVS models in parallel and distributed environments based on the WARPED kernel, an implementation of the Time Warp protocol. The optimistic simulator PCD++, built as a new simulation engine for CD++, is a toolkit that implements the DEVS and Cell-DEVS formalisms. We redesign algorithms in CD++ to carry out optimistic simulations using a non-hierarchical approach that reduces the communication overhead. The message-passing organization is analyzed using a high-level abstraction referred to as wall clock time slice. We propose a two-level user-controlled state-saving mechanism to achieve efficient and fleXible state saving at runtime. Various optimization strategies are applied to PCD++ and their effects are analyzed quantitatively, including a risk-free message type-based state-saving strategy to reduce the number of states saved during the simulation significantly, and a one log file per node strategy to break the bottleneck caused by file I/O operations. It is shown that PCD++ markedly outperforms other alternatives and considerable speedups can be achieved in parallel and distributed simulations.