We present two GVT computation algorithms for PDES techniques with event based activities, and relying on a space-time memory abstraction. Algorithm 2 involves a modification in the activity control, and is based on a...
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We present two GVT computation algorithms for PDES techniques with event based activities, and relying on a space-time memory abstraction. Algorithm 2 involves a modification in the activity control, and is based on an epoch coloring scheme. The effect of the modification is assessed through an experimental study on a simulator implemented in the Linda coordination language. Experiments are performed on a cluster of workstations, and show that the modified activity control discipline is able to enhance performances.
This paper describes a new, auto-adaptive algorithm for dead reckoning in DIS. In general dead-reckoning algorithms use a fixed threshold to control the extrapolation errors. Since a fixed threshold cannot adequately ...
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This paper describes a new, auto-adaptive algorithm for dead reckoning in DIS. In general dead-reckoning algorithms use a fixed threshold to control the extrapolation errors. Since a fixed threshold cannot adequately handle the dynamic relationships between moving entities, a multi-level threshold scheme is proposed. The definition of threshold levels is based on the concepts of area of interest (AOI) and sensitive region (SR), and the levels of threshold are adaptively adjusted based on the relative distance between entities during the simulation. Various experiments were conducted. The results show that the proposed auto-adaptive dead reckoning algorithm can achieve considerable reduction in update packets without sacrificing accuracy in extrapolation.
This paper presents the SEEDS simulation environment for the evaluation of distributed traffic control systems. Starting with an overview of the general simulator architecture, the software modules and the derived har...
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This paper presents the SEEDS simulation environment for the evaluation of distributed traffic control systems. Starting with an overview of the general simulator architecture, the software modules and the derived hardware architecture of the simulation environment are described with respect to performance requirements. The communication architecture of the SEEDS simulator is based on the OMG's CORBA standard and the DIS simulation protocol. With the SEEDS prototype simulating airport ground-traffic, performance measurements evaluating critical design and implementation decisions are described. The main aspects of the performance analysis are the attained application performance using CORBA and DIS as communication middle-ware, and the scalability of the overall approach. The evaluation shows the appropriateness of the design of the simulation environment and the derived hard- and software architecture, which is flexible and open to further extensions. Moreover, the combination of CORBA and DIS provides a suited platform for distributed interactive simulation purposes because of the adequate performance, high scalability, and the high-level programming model which allows to rapidly develop and maintain complex distributed applications with high-performance requirements.
parallel discrete event simulation algorithms are usually based on time stamp ordering of events. distributed virtual environment (DVE) applications such as DIS typically use unordered event delivery. A partial order ...
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parallel discrete event simulation algorithms are usually based on time stamp ordering of events. distributed virtual environment (DVE) applications such as DIS typically use unordered event delivery. A partial order called approximate time (AT) is proposed to order events in both domains, facilitating reuse of simulations across DVE and analysis applications. A variation on AT-order called approximate time causal (ATC) order is also described. Synchronisation algorithms to realize these orderings are presented as well as performance measurements on a workstation cluster. A long-term goal of this work is to use AT and ATC order to exploit temporal uncertainty in the model to achieve efficient conservative parallelsimulation despite little or no lookahead, a long-standing problem in the field.
Ordering of simultaneous events in DES is an important issue as it has an impact on modelling expressiveness, model correctness as well as causal dependencies. In sequential DES this is a problem which has attracted m...
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Ordering of simultaneous events in DES is an important issue as it has an impact on modelling expressiveness, model correctness as well as causal dependencies. In sequential DES this is a problem which has attracted much attention over the years and most systems provide the user with tools to deal with such issues. This has also attracted some attention within the PDES community and we present an overview of these efforts. We have, however, not yet found a scheme which provides us with the desired functionality. Thus, we present and evaluate some simple schemes to achieve a well defined ordering of events and means to identify both causally dependent and independent events with identical timestamps in the context of optimistic simulations. These schemes should be applicable also to conservative PDES.
Most successful examples of parallelsimulation models were developed for parallel execution, from the beginning. A number of simulation models are designed only for sequential simulation, even in languages like PARSE...
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Most successful examples of parallelsimulation models were developed for parallel execution, from the beginning. A number of simulation models are designed only for sequential simulation, even in languages like PARSEC, that support both sequential and parallelsimulation algorithms. Converting such simulation models to a form that yields good performance with a parallel implementation can be non-trivial. We describe a case study showing this conversion process for a simulation model of replicated file systems. The details of the major steps taken in converting the simulation into a parallelsimulation are presented: correctness changes; performance changes such as communication topology simplification and lookahead specification; and modeling changes to eliminate performance bottlenecks. The details and performance improvements of each step are presented.
The simulation of incompressible fluids is one of the important problem classes in computational fluid dynamics. We consider a simulation algorithm for the convection in binary fluid mixtures, a problem where a quite ...
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The simulation of incompressible fluids is one of the important problem classes in computational fluid dynamics. We consider a simulation algorithm for the convection in binary fluid mixtures, a problem where a quite simple model describes a very complex behavior. In a parallel implementation on an IBM SP2, we investigate several implementation strategies involving different data layouts and communication organizations.
We have developed a set of performance prediction tools which help to estimate the achievable speedups from parallelizing a sequential simulation. The tools focus on two important factors in the actual speedup of a pa...
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We have developed a set of performance prediction tools which help to estimate the achievable speedups from parallelizing a sequential simulation. The tools focus on two important factors in the actual speedup of a parallelsimulation program: (a) the simulation protocol used, and (b) the inherent parallelism in the simulation model. The first two tools are a performance/parallelism analyzer for a conservative, asynchronous simulation protocol, and a similar analyzer for a conservative, synchronous ('super-step') protocol. Each analyzer allows us to study how the speedup of a model changes with increasing number of processors, when a specific protocol is used. The third tool - a critical path analyzer - gives an ideal upper bound to the model's speedup. This paper gives an overview of the prediction tools, and reports the predictions from applying the tools to a discrete-event wafer fabrication simulation model. The predictions are close to speedups from actual parallel implementations. These tools help us to set realistic expectations of the speedup from a parallelsimulation program, and to focus our work on issues which are more likely to yield performance improvement.
This paper presents a checkpointing scheme for optimistic simulation which is a mixed approach between periodic and probabilistic checkpointing. The latter, basing on statistical data collected during the simulation, ...
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This paper presents a checkpointing scheme for optimistic simulation which is a mixed approach between periodic and probabilistic checkpointing. The latter, basing on statistical data collected during the simulation, aims at recording as checkpoints states of a logical process that have high probability to be restored due to rollback (this is done in order to make those states immediately available). The periodic part prevents performance degradation due to state reconstruction (coasting forward) cost whenever the collected statistics do not allow to identify states highly likely to be restored. Hence, this scheme can be seen as a highly general solution to tackle the checkpoint problem in optimistic simulation. A performance comparison with previous solutions is carried out through a simulation study of a store-and-forward communication network in a two-dimensional torus topology.
In optimistic parallelsimulations, state-saving techniques have been traditionally used to realize rollback. In this article, we propose reverse computation as an alternative approach, and compare its execution perfo...
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In optimistic parallelsimulations, state-saving techniques have been traditionally used to realize rollback. In this article, we propose reverse computation as an alternative approach, and compare its execution performance against that of state-saving. Using compiler techniques, we describe an approach to automatically generate reversible computations, and to optimize them to transparently reap the performance benefits of reverse computation. For certain fine-grain models, such as queuing network models, we show that reverse computation can yield significant improvement in execution speed coupled with significant reduction in memory utilization, as compared to traditional state-saving. On sample models using reverse computation, we observe as much as three-fold improvement in execution speed over traditional state-saving.
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