Opportunities and Challenges of Modern Communication Architectures: Case Study with QsNet

We describe our efforts to scale message driven applica-tions to a large number of processors on an Alpha cluster interconnected by QsNet. The clustering technology QsNet has a network interface with a communication co-processor. The presence of the co-processor minimizes main processor participation in message passing. We show the advantages of the communication co-processor for message driven ap-plications. To scale fine-grained message driven appli-cations to a large number of processors we had to over-come several hardware, software and operating system hin-drances. We describe them in detail and present solutions for them. We use NAMD, a molecular dynamics program, as a case study for many of our performance optimizations.