On the impact of message packetization in networks of workstations with irregular topology

Networks of workstations (NOWs) are becoming an increasingly popular alternative to parallel computers for those applications with high needs of resources such as memory capacity and input/output storage space, and also for small scale parallel computing. Usually, the software messaging layers in these systems become a bottleneck due to the overhead they introduce. Some proposals like FM and BIP considerably reduce this overhead by splitting long messages into several packets. These proposals have been shown to improve communication performance. However, the effect of message packetization on the network interconnects has not been analyzed yet. In this paper we examine the effect of message packetization from the point of view of the interconnection network in the context of bimodal traffic. Two different routing algorithms have been considered: up*/down* and minimal adaptive routing. Our study shows that when the up */down* routing algorithm is used, message packetization dramatically increases latency and reduces throughput for both long and short messages. On the other hand, if minimal adaptive routing is used, short messages could benefit from message packetization, but at the cost of increasing latency for long messages. In any case, network throughput is considerably reduced.