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Adaptive memory management and optimism control in time warp

Published:01 April 1997Publication History
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Abstract

It is widely believed that the Time Warp protocol for parallel discrete event simulation is prone to two potential problems: an excessive amount of wasted, rolled back computation resulting from “rollback thrashing” behaviors, and inefficient use of memory, leading to poor performance of virtual memory and/or multiprocessor cache systems. An adaptive mechanism is proposed based on the Cancelback memory management protocol for shared-memory multiprocessors that dynamically controls the amount of memory used in the simulation in order to maximize performance. The proposed mechanism is adaptive in the sense that it monitors the execution of the Time Warp program, and using simple models, automatically adjusts the amount of memory used to reduce Time Warp overheads (fossil collection, Cancelback, the amount of rolled back computation, etc.) to a manageable level. We describe an implementation of this mechanism on a shared memory, Kendall Square Research KSR-1, multiprocessor and demonstrate its effectiveness in automatically maximizing performance while minimizing memory utilzation, for several synthetic and benchmark discrete event simulation applications. We also demonstrate the adaptive ability of the mechanism by showing that it “tracks” the time-varying nature of a communication network simulation.

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  1. Adaptive memory management and optimism control in time warp

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          Anthony Joseph Duben

          Time Warp is an optimistic synchronization protocol in parallel simulation computations. At runtime, it detects out-of-sequence events and recovers by rolling back the calculation to properly account for the events. Time Warp has two major problems: excessive amounts of wasted, rolled back computation, and inefficient use of memory, leading to poor performance of virtual memory or cache systems. Das and Fujimoto present an adaptive memory management system that can cope with both of these problems. The solution monitors the execution of the Time Warp program and, based on the runtime data colle cted, automatically adjusts the amount of memory used to reduce the Time Warp overhead. It requires only a modest amount of memory beyond that required for sequential execution. The authors thoroughly review the Time Warp method, the nature of the problems discovered, and previous proposals to deal with them. They remark that the two problems mentioned above were considered independently in the past. Their contribution is a method by which both problems can be solved using a single approach based on the Cancelback protocol. The Cancelback protocol is presented in terms of quantitative measures of the usage of the memory buffers and estimated times of moving and processing data among them. These measures comprise the data gathered in the Time Warp program, and they enable the system to operate flexibly with widely varying workloads in a fully adaptive manner. Two test problems are used to demonstrate and illustrate the adaptive memory management method—a symmetric homogeneous workload (PHOLD) and an open asymmetric flow network based on electric power grids. A third application, a personal communication service network, is also discussed as a benchmark case. All of the computational experiments are presented in detail.

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            cover image ACM Transactions on Modeling and Computer Simulation
            ACM Transactions on Modeling and Computer Simulation  Volume 7, Issue 2
            April 1997
            130 pages
            ISSN:1049-3301
            EISSN:1558-1195
            DOI:10.1145/249204
            Issue’s Table of Contents

            Copyright © 1997 ACM

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            Association for Computing Machinery

            New York, NY, United States

            Publication History

            • Published: 1 April 1997
            Published in tomacs Volume 7, Issue 2

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