Limitations of cache prefetching on a bus-based multiprocessor

• Published in: International Symposium on Computer Architecture: Proceedings of the 20th annual international symposium on Computer architecture; 16-19 May 1993 pp. 278 - 288
• Main Authors: Tullsen, Dean M., Eggers, Susan J.
• Format: Conference Proceeding
• Language: English
• Published: New York, NY, USA ACM 01.05.1993
• Series: ACM Conferences
• Subjects: Computer systems organization > Architectures > Parallel architectures > Multiple instruction, multiple data; Computing methodologies > Modeling and simulation > Model development and analysis > Modeling methodologies; Computing methodologies > Parallel computing methodologies > Parallel programming languages; General and reference > Cross-computing tools and techniques > Performance; Software and its engineering > Software notations and tools > Compilers; Software and its engineering > Software notations and tools > General programming languages > Language types > Parallel programming languages
• ISBN: 0818638109; 9780818638107
• DOI: 10.1145/165123.165163

Compiler-directed cache prefetching has the potential to hide much of the high memory latency seen by current and future high-performance processors. However, prefetching is not without costs, particularly on a multiprocessor. Prefetching can negatively affect bus utilization, overall cache miss rates, memory latencies and data sharing. We simulated the effects of a particular compiler-directed prefetching algorithm, running on a bus-based multiprocesssor. We showed that, despite a high memory latency, this architecture is not very well-suited for prefetching. For several variations on the architecture, speedups for five parallel programs were no greater than 39%, and degradations were as high as 7%, when prefetching was added to the workload. We examined the sources of cache misses, in light of several different prefetching strategies, and pinpointed the causes of the performance changes. Invalidation misses pose a particular problem for current compiler-directed prefetchers. We applied two techniques that reduced their impact: a special prefetching heuristic tailored to write-shared data, and restructuring shared data to reduce false sharing, thus allowing traditional prefetching algorithms to work well.