Efficient Barriers for Distributed Shared Memory Computers

Barrier algorithms are central to the performance of numerous algorithms on scalable, high-performance architectures. Numerous barrier algorithms have been suggested and studied for Non-Uniform Memory Access (NUMA) architectures, but less work has been done for Cache Only Memory Access (COMA) or attraction memory 2] architectures such as the KSR-1. In this paper, we present two new barrier algorithms that ooer the best performance we have recorded on the KSR-1 distributed cache multiprocessor. We discuss the trade-oos and the performance of seven algorithms on two architectures. The new barrier algorithms adapt well to a hierarchical caching memory model and take advantage of parallel communication ooered by most multiprocessor interconnection networks. Performance results are shown for a 256-processor KSR-1 and a 20-processor Sequent Symmetry .