Flow Control and Dynamic Load Balancing in Time Warp

We present, in this paper, an algorithm which integrates flow control and dynamic load balancing in Time Warp. The algorithm is intended for use in a distributed memory envi-ronment such as a cluster of workstations connected by a high speed switch. Our flow control algorithm makes use of stochastic learning automata and is similar to the leaky-bucket flow control algorithm used in computer networks. It regulates the flow of messages between processors continu-ously throughout the course of the simulation, while the dy-namic load balancing algorithm is invoked only when a load imbalance is detected. We compare the performance of the flow control algo-rithm, the dynamic load balancing algorithm and the in-tegrated algorithm with that of a simulation without these controls. We simulated large shuffle ring networks with and without hot spots and a PCS network on an SGI Origin 2000 system. Our results indicate that the flow control scheme alone succeeds in greatly reducing the number and length of rollbacks as well as the number of anti-messages, thereby in-creasing the number of non-rolled back messages processed per second. It results in a large reduction in the amount of memory used and outperforms the dynamic load balancing algorithm for these measures. The integrated scheme pro-duces even better results for all of these measures and results in reduced execution times