Workstation and PC clusters interconnected by SCI (scalable coherent interface) are very promising technologies for high-performance cluster computing. Using commercial SBus to SCI interface cards and system software and drivers, a two-workstation cluster has been constructed for initial testing and evaluation. The PVM system has been adapted to operate on this cluster using both raw channel and shared-memory access to the SCI interconnect, and preliminary communications performance tests have been carried out. To achieve mutual exclusion in accessing shared-memory segments, two protocols were used.
Our preliminary results indicate that communications throughput in the range of 17.7 Mbytes/s, and round-trip latencies of 80 ยตs using the first and 140 ยตs using the second protocol, can be obtained on SCI clusters. These figures are significantly better (by a factor of 2 to 4) for small and large messages than those attainable on Fast Ethernet LANs. Since these performance results are very encouraging, we expect that, in the very near future, SCI networks will be capable of delivering several tens of Mbytes/s bandwidth and a few tens of microseconds latencies, and will significantly enhance the viability of cluster computing.