Load Balancing Strategies for Time Warp on Multi-User Workstations

Abstract

This paper describes load balancing techniques for the Time Warp distributed synchronization technique for object-oriented simulation. The Time Warp system distributes objects across nodes and provides optimistic concurrency control. Our implementation is Lisp-based and executes on a network of UNIX-based workstations, where system load varies depending on the number of users and processes. This technique achieves a balanced load by first determining if the load is unbalanced. Then if it is unbalanced, the system must determine which machine is the most underloaded and migrate an object to that machine. Several object-migration techniques were attempted before arriving at a method efficient enough to make dynamic load balancing viable. We discuss a static balancing technique to start the system with a balanced load, but variance in object behavior and individual workstation load require a dynamic load monitor. Time Warp simulations executed under dynamic balancing versus static load balancing are five to 10 times faster.