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The implications of working set analysis on supercomputing memory hierarchy design

Underwood, Keith; Rodrigues, Arun

Supercomputer architects strive to maximize the performance of scientific applications. Unfortunately, the large, unwieldy nature of most scientific applications has lead to the creation of artificial benchmarks, such as SPEC-FP, for architecture research. Given the impact that these benchmarks have on architecture research, this paper seeks an understanding of how they relate to real-world applications within the Department of Energy. Since the memory system has been found to be a particularly key issue for many applications, the focus of the paper is on the relationship between how the SPEC-FP benchmarks and DOE applications use the memory system. The results indicate that while the SPEC-FP suite is a well balanced suite, supercomputing applications typically demand more from the memory system and must perform more 'other work' (in the form of integer computations) along with the floating point operations. The SPEC-FP suite generally demonstrates slightly more temporal locality leading to somewhat lower bandwidth demands. The most striking result is the cumulative difference between the benchmarks and the applications in terms of the requirements to sustain the floating-point operation rate: the DOE applications require significantly more data from main memory (not cache) per FLOP and dramatically more integer instructions per FLOP.