Impact of Latency on Applications’ Performance
Rossen Dimitrov · 2001
This paper investigates the impact of point-topoint latency on applications’ performance on clusters of workstations interconnected with high-speed networks. At present, clusters are often evaluated through comparison of point-to-point latency and bandwidth obtained by ping-pong tests. This paper shows that this approach to performance evaluation of clusters has limited validity and that latency has minimal impact on a large group of applications that use mediumto coarse-grain data-parallel algorithms. Message-passing systems with low latency often use polling for message completion, which leads to tight synchronization between the communicating processes and high CPU overhead. Systems with asynchronous message completion have higher point-to-point latency for short messages but offer a number of highperformance mechanisms such as overlapping of computation and communication, independent message progress, efficient collective algorithms, asynchronous processing of communicating nodes, and exploitation of temporal locality. These mechanisms can be effectively implemented on current high-speed networks with intelligent interface controllers capable of bus-master transfers on host peripheral busses. Although message-passing systems that use asynchronous completion notification have higher point-to-point latency than systems with polling, they can offer opportunities for performance gains with far greater overall impact.