Performance evaluation of a cluster-based multiprocessor built from ATM switches and bus-based multiprocessor servers

We consider a network of workstations (NOW) organization consisting of a number of bus-based multiprocessor servers interconnected by an ATM switch. A shared-memory model is supported by distributed virtual shared memory (DVSM) and this paper focuses on the access penalties incurred by (1) ATM and (2) the DVSM software. First, through detailed architectural simulations we find that while the bandwidth and the latency of the ATM switch fabrics are found to be acceptable, the latency incurred by commercially available ATM interfaces has a first order effect on the performance. We also study the effects of various scheduling policies for the coherence handlers. Our data suggest that since the probability of finding an idle processor within a cluster is high, a good policy is to schedule it there instead of letting an extra compute processor execute coherence handlers. Overall, by adjusting the adaptation layer of ATM to a DVSM system we find that ATM is a promising technology for these kinds of systems.