System Buffer Size Requirements: An Application's Perspective

This paper entails an in-depth study of the system bu er size requirements for parallel scienti c applications that communicate regularly with four or six neighbors. The goal of this study is to address two major issues: (1) for future system designs, which system features signi cantly impact the system bu er size requirements and (2) for systems where users can set the system bu er size (e.g., IBM SP2 and SGI-Cray T3E), what is a good estimate to use for good performance. We propose an analytical model of bu er size requirements for message passing systems. This model is validated experimentally for the IBM SP2 system. We then use the model to perform sensitivity analysis on bu er size requirements with varying network bandwidth, receive latency, memory copy rate, delay between messages, and di erent number of messages. The analytical results indicate that the two major factors that a ect the bu er size are the delay between messages and the increase in network bandwidth. Further, these two factors are related. The network bandwidth has little impact on bu er size requirements when the delay is small, but has signi cant impact when the delay is large. The receive startup latency and receive memory copy rate have very little impact on bu er size requirements.