SUMMARY Adaptive routing algorithms, which dynamically select the route of a packet, have been widely studied for interconnection networks in massively parallel computers. An output selection function (OSF), which decides the output channel when some legal channels are free, is essential for an adaptive routing. In this paper, we propose a simple and efficient OSF called minimal multiplexed and least-recently-used (MMLRU). The MMLRU selection function has the following simple strategies for distributing the traffic: 1) each router locally grasps the congestion information by the utilization ratio of its own physical channels; 2) it is divided into the two selection steps, the choice from available physical channels and the choice from available virtual channels. The MMLRU selection function can be used on any type of network topology and adaptive routing algorithm. Simulation results show that the MMLRU selection function improves throughput and latency especially when the number of dimension becomes larger or the number of nodes per dimension become larger. key words: output selection function, adaptive routing, virtual channel, interconnection networks, massively parallel computers 1.

Injection on Simulated Hardware) is a simulator to explore the design space of high-performance networks. The simulator features a high modularity and is configurable by plug-ins. The simulated network is scalable to a large number of nodes and its modules are parameterizable to model timing, delays and buffer sizes. A simple and universal method to generate communication patterns is based on the single program multiple data (SPMD) programming model. Various topologies from distributed to centralized switches with a extendable variety of routing and arbitration functions can be generated easily. Extensive possibilities to collect both performance and statistical data gives the network designer a large set of data to prove the design decisions. Accuracy is proven by comparing the simulation results to real performance measurements of an existing network.