Improving the performance of bristled CC-NUMA systems using virtual channels and adaptivity
José F. Martínez, Josep Torrellas, José F. Duato · 1999
Current high-end parallel systems achieve low-latency, high-bandwidth network communication through the use of aggressive design techniques and expensive mechanical and electrical parts. High-speed interconnection networks, which are crucial to achieve acceptable system performance, may account for an important fraction of the total cost of the machine. To reduce the network cost and still maintain scalability, bristled configurations, in which each router connects to several processing nodes, pose an attractive alternative. Their lower bandwidth, however, may adversely affect the efficiency of the parallel codes. In this paper, we show how virtual channels and adaptive routing can make bristled systems more attractive: overall performance improves in congested scenarios while remaining practically unaltered under light traffic conditions. Experimental results are obtained by using execution-driven simulation of a complete state-of-the-art CC-NUMA system, with dynamic superscalar processors and contemporary pipelined routers. The results show that, in bristled hypercubes with 2 processing nodes per router, SPLASH-2 applications with significant communication run 5-15% faster if we make use of virtual channels and adaptive routing. The resulting systems are only 1-10% slower than systems with non-bristled hypercubes and similar routing support, even though the former only need about half of the network hardware components present in the latter. Additionally, virtual channels and adaptivity are shown to be of negligible effect in non-bristled hypercubes. This work was supported in part by the National Science Foundation under grants NSF Young Investigator Award MIP-9457436, ASC9612099 and MIP-9619351, DARPA Contract DABT63-95-C-0097, NASA Contract NAG-1-613, NCSA Gran...