The status of the time warp operating system

Jefferson, David; Beckman, Brian; Blume, L.; Diloreto, M.; Hontalas, Philip; Reiher, Peter; Sturdevant, K.; Tupman, Jack; Wedel, John J.; Wieland, Frederick; Younger, H. C.

doi:10.1145/62297.62392

Cited by 14 publications

(14 citation statements)

References 4 publications

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“…16 Loss of parallelism is represented in the performance curves as 1) larger event execution time because of cancellations of correct events and rollbacks followed by reexecutions of the corresponding sender events, and 2) busy wait time for memory to allow the GVT regulator to progress.…”

Section: Discussionmentioning

confidence: 99%

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An empirical evaluation of performance-memory trade-offs in time warp

Das

Fujimoto

1997

IEEE Trans. Parallel Distrib. Syst.

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Abstract-The performance of the Time Warp mechanism is experimentally evaluated when only a limited amount of memory is available to the parallel computation. An implementation of the cancelback protocol is used for memory management on a shared memory architecture, viz., KSR to evaluate the performance vs. memory tradeoff. The implementation of the cancelback protocol supports canceling back more than one memory object when memory has been exhausted (the precise number is referred to as the salvage parameter) and incorporates a non-work-conserving processor scheduling technique to prevent starvation.Several synthetic and benchmark programs are used that provide interesting stress cases for evaluating the limited memory behavior. The experiments are extensively monitored to determine the extent to which various factors may affect performance. Several observations are made by analyzing the behavior of Time Warp under limited memory: 1) Depending on the available memory and asymmetry in the workload, canceling back several memory objects at one time (i.e., a salvage parameter value of more than one) improves performance significantly, by reducing certain overheads. However, performance is relatively insensitive to the salvage parameter except at extreme values. 2) The speedup vs. memory curve for Time Warp programs has a well-defined knee before which speedup increases very rapidly with memory and beyond which there is little performance gain with increased memory. 3) A performance nearly equivalent to that with large amounts of memory can be achieved with only a modest amount of additional memory beyond that required for sequential execution, if memory management overheads are small compared to the event granularity. These results indicate that contrary to the common belief, memory usage by Time Warp can be controlled within reasonable limits without any significant loss of performance.

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Section: Discussionmentioning

confidence: 99%

“…In message sendback, GVT is the minimum of 1) all local clocks and 2) send times of all messages in transit [18]. This definition is also used in TWOS [16] that implements message sendback in its flow control. 4.…”

Section: Active Memory Management Schemes For Time Warpmentioning

confidence: 99%

An empirical evaluation of performance-memory trade-offs in time warp

Das

Fujimoto

1997

IEEE Trans. Parallel Distrib. Syst.

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“…Conservative protocols limit the amount of parallelism, as potentially conflicting events are serialized [10,20]. Optimistic protocols, on the other hand, use rollbacks to resolve conflicts [24]. Time-stepped applications typically eschew these approaches, because the high frequency of local interactions causes numerous conflicts and rollbacks, limiting scalability.…”

Section: Related Workmentioning

confidence: 99%

Making time-stepped applications tick in the cloud

Zou

Wang

Salles

et al. 2011

Proceedings of the 2nd ACM Symposium on Cloud Computing

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Scientists are currently evaluating the cloud as a new platform. Many important scientific applications, however, perform poorly in the cloud. These applications proceed in highly parallel discrete time-steps or "ticks," using logical synchronization barriers at tick boundaries. We observe that network jitter in the cloud can severely increase the time required for communication in these applications, significantly increasing overall running time.In this paper, we propose a general parallel framework to process time-stepped applications in the cloud. Our framework exposes a high-level, data-centric programming model which represents application state as tables and dependencies between states as queries over these tables. We design a jitter-tolerant runtime that uses these data dependencies to absorb latency spikes by (1) carefully scheduling computation and (2) replicating data and computation. Our data-driven approach is transparent to the scientist and requires little additional code. Our experiments show that our methods improve performance up to a factor of three for several typical timestepped applications.

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“…This may require the cancellation of messages that have been sent by the logical process. The Time Warp mechanism, based on the Virtual Time paradigm, is the best known optimistic protocol [Jefferson 1985, Jefferson and Sowizral 1985, Jefferson et al, 1987.…”

Section: Introductionmentioning

confidence: 99%

Extending the DEVS formalism for massively parallel simulation

Wang

Zeigler

1993

Discrete Event Dyn Syst

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Abstract. The use of mulfiprocessors for discrete event simulation is an active research area where work has focused on strategies for model execution with little regard for the underlying formalism in which models may be expressed. However, a formalism-based approach offers several advantages including the ability to migrate models from sequential to parallel platforms and the ability to calibrate simulation architectures to model structural properties. In this article, we extend the DEVS (discrete event system specification) formalism, originally developed for sequential simulation, to accommodate the full potential of parallel processing. The extension facilitates exploitation of both internal and external event parallelism manifested in hierarchical, modular DEVS models. After developing a mapping of the extended formalism to parallel architectures, we describe an implementation of the approach on a massively parallel architecture, the Connection Machine. Execution results are discussed for a class of models exhibiting high external and internal event parallelism, the so-called broadcast models. These verify the tenets of the underlying theory and demonstrate that significant reduction in execution time is possible compared to the same model executed in serial simulation.

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The status of the time warp operating system

Cited by 14 publications

References 4 publications

An empirical evaluation of performance-memory trade-offs in time warp

An empirical evaluation of performance-memory trade-offs in time warp

Making time-stepped applications tick in the cloud

Extending the DEVS formalism for massively parallel simulation

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