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Understanding supercritical speedup

Published: 01 July 1994 Publication History

Abstract

Simulations running under Time Warp using lazy cancellation can beat the bound given by the critical path. We explain this phenomenon to be the result of a kind of intra-object parallelism. Specifically, we show that instances of beating the critical path, called supercritical speedup, are made possible by messages that are independent of some event which precedes the message. This insight leads to a new definition for the critical path which is a tighter lower bound on Time-Warp simulations using lazy cancellation than any previously proposed. These results suggest criteria for choosing between lazy and aggressive cancellation.

References

[1]
Orna Berry and David jefferson. Critical path analysis of distributed simulation. In Proceedings of the SCS Mult~conference on Distributed Simulation, pages 122-127. Society for Computer Simulation, January 1985.
[2]
K. Mani Chandy and Rivi Sherman. Space-time and simulation. In Proceedzngs of the SCS Multiconference on Distributed Simulatwn, pages 53-57. Society for Computer Simulation, March 1989.
[3]
David R. Jefferson. Virtual time. A CM Transactions on Programming Languages and Systems, 7(3):404-425, July 1985.
[4]
David Jefferson and Peter Reiher. Supercritical speedup, in P4th Annual Simulation Symposium, pages 159-168. IEEE Computer Society Press, April 1991.
[5]
Yi-Bing Lin and Edward D. Lazowska. A study of time warp rollback mechananisms. A CM Transactions on Modeling and Computer Simulations, 1 (1):51-72, January 1991.
[6]
Darrin West. Optimizing time warp: Lazy rollback and lazy reevaluation. Master's thesis, University of Calgary, January 1988.

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Ernest H. Page

The author characterizes the speedup of parallel discrete event simulation (PDES) programs relative to their concomitant critical path estimations. The ability of a parallel implementation to outperform the critical path is related to the level of intra-object event independence in the model. Based on a formalization of intra-object event independence, Gunter describes a new approach to calculating the critical path of a simulation and shows that it provides a tighter lower bound approximation than previously known techniques. The paper is technically sound and provides insight into a fundamental problem for PDES. The presentation is somewhat terse, however, and assumes the reader is familiar with several basic PDES premises, such as state space partitioning in model development. The interested reader might also refer to Lin [1] for a more detailed treatment of the concepts.

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Information & Contributors

Information

Published In

cover image ACM SIGSIM Simulation Digest
ACM SIGSIM Simulation Digest  Volume 24, Issue 1
July 1994
192 pages
ISSN:0163-6103
DOI:10.1145/195291
Issue’s Table of Contents
  • cover image ACM Conferences
    PADS '94: Proceedings of the eighth workshop on Parallel and distributed simulation
    August 1994
    196 pages
    ISBN:1565550277
    DOI:10.1145/182478

Publisher

Association for Computing Machinery

New York, NY, United States

Publication History

Published: 01 July 1994
Published in SIGSIM Volume 24, Issue 1

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