Opportunities and challenges of modern communication architectures: case study with QsNet

Summary form only given. We describe our efforts to scale message driven applications to a large number of processors on an Alpha cluster interconnected by QsNet. The clustering technology QsNet has a network interface with a communication coprocessor. The presence of the coprocessor minimizes main processor participation in message passing. We show the advantages of the communication coprocessor for message driven applications. To scale fine-grained message driven applications to a large number of processors we had to overcome several hardware, software and operating system hindrances. 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.