Parallel Distributed Computing on Sci Workstation Clusters: Early Experiences

Workstation and PC clusters interconnected by SCI (Scalable Coherent Interface) are very promising technologies for high performance cluster computing. Using commercial SBus-SCI interface cards and early system software and drivers, a two-SPARCstation cluster has been constructed for initial testing and evaluation. PVM direct task-to-task data transfers have been adapted to operate on this cluster using raw device access to the SCI interconnect (message passing), and preliminary communications performance tests have been carried out. Our early results with PVM direct data transfers over SCI show a two to threefold throughput improvement over the fastest Ethernet implementation. However, message-passing latencies over SCI are in the millisecond range, comparable to TCP-based communication latencies. Initial analysis suggests that performance is primarily limited by sub-optimal functionality and eeciency available with the rst-generation SBus-SCI hardware and software, in particular the SCI device driver. The utilization of shared memory based interprocess communication promises to improve latency gures signiicantly, into the range of 100 microseconds.