Simultaneous multithreading maximizing on-chip parallelism

• Published in: International Symposium on Computer Architecture: Proceedings of the 22nd annual international symposium on Computer architecture; 22-24 June 1995 pp. 392 - 403
• Main Authors: Tullsen, Dean M., Eggers, Susan J., Levy, Henry M.
• Format: Conference Proceeding
• Language: English
• Published: New York, NY, USA ACM 01.05.1995; IEEE
• Series: ACM Conferences
• Subjects: Computer science; Computer systems organization > Architectures > Parallel architectures; Computing methodologies > Modeling and simulation > Model development and analysis > Modeling methodologies; Delay; General and reference > Cross-computing tools and techniques > Performance; Modems; Multithreading; Parallel processing; Permission; Samarium; Switches; Throughput; Yarn
• ISBN: 9780897916981; 0897916980
• ISSN: 1063-6897; 2575-713X
• DOI: 10.1145/223982.224449

This paper examines simultaneous multithreading, a technique permitting several independent threads to issue instructions to a superscalar's multiple functional units in a single cycle. We present several models of simultaneous multithreading and compare them with alternative organizations: a wide superscalar, a fine-grain multithreaded processor, and single-chip, multiple-issue multiprocessing architectures. Our results show that both (single-threaded) superscalar and fine-grain multithreaded architectures are limited their ability to utilize the resources of a wide-issue processor. Simultaneous multithreading has the potential to achieve 4 times the throughput of a superscalar, and double that of fine-grain multithreading. We evaluate several cache configurations made possible by this type of organization and evaluate tradeoffs between them. We also show that simultaneous multithreading is an attractive alternative to single-chip multiprocessors; simultaneous multithreaded processors with a variety of organizations outperform corresponding conventional multiprocessors with similar execution resources.While simultaneous multithreading has excellent potential to increase processor utilization, it can add substantial complexity to the design. We examine many of these complexities and evaluate alternative organizations in the design space.