Efficient adaptive routing in networks of workstations with irregular topology

Abstract

Networks of workstations are rapidly emerging as a cost-effective alternative to parallel computers. Switch-based interconnects with irregular topologies allow the wiring flexibility, scalability and incremental expansion capability required in this environment. The irregularity also makes routing and deadlock avoidance on such systems quite complicated. Current proposals avoid deadlock by removing cyclic dependencies between channels. As a consequence, many messages are routed following non-minimal paths, increasing latency and wasting resources. In this paper, we propose a general methodology for the design of adaptive routing algorithms for networks with irregular topology. These routing algorithms allow messages to follow minimal paths in most cases, reducing message latency and increasing network throughput. The methodology is based on the application of the theory of deadlock avoidance proposed in [14], which increases routing flexibility by allowing cyclic dependencies between channels. As an example of application, we propose an adaptive routing algorithm for Autonet. It can be implemented either by duplicating physical channels or by splitting each physical channel into two virtual channels. In the former case, the implementation does not require a new switch design. It only requires changing the routing tables and adding links in parallel with existing ones, taking advantage of spare switch ports. In the latter case, a new switch design is required but the network topology is not changed. Preliminary evaluation results show that the new routing algorithm is able to increase throughput for random traffic by a factor of up to 2.8 with respect to the original algorithm, also reducing latency.

This work was supported by the Spanish CICYT under Grant TIC94-0510-C02-01