Latency Metric: An Experimental Method for Measuring and Evaluating Parallel Program and Architecture Scalability

Latency measures the delay caused by communication between processors and memory modules over the network in a parallel system. Using intensive measurements and simulation, we show that network latency forms a major obstacle to improve parallel computing performance and scalability. We present an experimental metric, using network latency to measure and evaluate the scalability of parallel programs and architectures. This latency metric is an extension to the isoeeciency function 3] and isospeed metric 9]. We give a measurement method for using this latency metric, and report the experimental results of evaluating the scalabilities of several scientiic computing algorithms on the KSR-1 shared-memory architecture. Our analysis and experiments show that the latency metric is a practical method to eeectively predict and evaluate scalability based on measured latencies inherent in the program and the architecture.