A New Theory of Deadlock-Free Adaptive Routing in Wormhole Networks

Second generation multicomputers use wormhole routing, allowing a very low channel setup time and drastically reducing the dependency between network latency and internode distance. Deadlock-free routing strategies have been developed, allowing the implementation of fast hardware routers that reduce the communicat ion bottleneck. Also, adaptive routing algorithms with deadlock-avoidance or deadlock-recovery techniques have been proposed for some topologies, being very effective and outperforming static strategies. This paper develops the theoretical background for the design of deadlock-free adaptive routing algorithms for wormhole networks. Some basic definitions and two theorems are proposed, developing conditions to verify that an adaptive algorithm is deadlock-free, even when there are cycles in the channel dependency graph. Also, two design methodologies are proposed. The first one supplies algorithms with a high degree of freedom, without increasing the number of physical channels. The second methodology is intended for the design of fault-tolerant algorithms. Some examples are given, showing the application of the methodologies. Finally, some simulations show the performance improvement that can be achieved by designing the routing algorithms with the new theory.