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Next: Introduction

Sustainable Memory Bandwidth in Current High Performance Computers

John D. McCalpin
Advanced Systems Division
Silicon Graphics, Inc.
mccalpin@sgi.com

Revised to October 12, 1995

Abstract:

As the ratio of cpu speed to memory speed continues to increase in high performance computers, sustained memory bandwidth obtainable by user codes is an obvious candidate for a figure of merit in the performance evaluation of computer systems for high-performance computing. Sustainable memory bandwidth has a straightforward and intuitive interpretation, and is likely to be well correlated with application performance for vector-style codes with low computational density and limited cache re-use.

Despite this apparent simplicity, the architectural factors which determine sustainable memory bandwidth are many and complex, with a number of interesting subtleties. Vendors very seldom make enough hardware details available to make accurate estimates of sustainable memory bandwidth possible. Therefore, I present the results of a broad survey of memory bandwidth for a large variety current computers, including uniprocessors, vector processors, shared-memory systems, and distributed-memory systems.

The results are analyzed in terms of the sustainable data transfer rates for uncached unit-stride vector operations for each machine, and for each class. Some trends in the ratio of floating-point performance to memory bandwidth are also presented and discussed.





John McCalpin
Tue Aug 20 20:43:16 PDT 1996