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.
We present a parallel simulator (SWiMNet) for PCS networks using a combination of optimistic and conservative paradigms. The proposed methodology exploits event precomputation permitted by model independence within th...
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We present a parallel simulator (SWiMNet) for PCS networks using a combination of optimistic and conservative paradigms. The proposed methodology exploits event precomputation permitted by model independence within the PCS components. The low percentage of blocked calls is exploited in the channel allocation simulation of precomputed events by means of an optimistic approach. Experiments were conducted with various call arrival rates and mobile host densities on a cluster of Pentium workstations. Performance results indicate that the SWiMNet achieves a speedup of 6 employing 8 workstations, and a speedup of 12 with 16 workstations.
Traditionally, parallel discrete-event simulators based on the Time Warp synchronization protocol have been implemented using either the shared memory programming model or the distributed memory, message passing progr...
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Traditionally, parallel discrete-event simulators based on the Time Warp synchronization protocol have been implemented using either the shared memory programming model or the distributed memory, message passing programming model. This was because the preferred hardware platform was either a shared memory multiprocessor workstation or a network of uniprocessor workstations. However, with the advent of clumps (cluster of shared memory multiprocessors), a change in this dichotomous view becomes necessary. We explore the design and implementation issues involved in exploiting this new platform for Time Warp simulations. Specifically, we present two generic strategies for implementing Time Warp simulators on clumps. In addition, we present our experiences in implementing these strategies on an extant distributed memory, message passing Time Warp simulator (WARPED). Preliminary performance results comparing the modified clump-specific simulation kernel to the unmodified distributed memory, message passing simulation kernel are also presented.
There are at least three major obstacles thwarting widespread adoption of parallel discrete-event simulation: lack of need; lack of tools; and lack of predictability in behavior and performance. The plain truth is tha...
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There are at least three major obstacles thwarting widespread adoption of parallel discrete-event simulation: lack of need; lack of tools; and lack of predictability in behavior and performance. The plain truth is that most simulation studies can be adequately done on ordinary serial computers. parallelsimulation tools are products of research efforts, and simply do not stand up to the demands of modern software engineering. The results of 20 years of research in parallelsimulation reveal it to be a highly complex endeavour, with performance results very much dependent on implementation details and model characteristics. The Scalable simulation Framework (SSF) is an effort to address some these concerns. It addresses lack of need in two ways; it provides a modeling API that is attractive both for serial and parallelsimulation, with parallel execution requiring no change to the model, and it targets large-scale telecommunication system modeling, an application area that requires the computational capabilities of parallelism. We address the concern over unpredictable behavior. We show how we measured the internal overheads of the Dartmouth implementation of the SSF API (DaSSF), and how those measurements can be used to predict the performance of a given model, using given features of the simulator, without having to run, or even build, the model.
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.
We present two GVT computation algorithms for PDES techniques with event based activities, relying on a space-time memory abstraction. Algorithm 2 involves a modification in the activity control, and is based on an ep...
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We present two GVT computation algorithms for PDES techniques with event based activities, 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 performance.
This paper introduces the Critical Channel Traversing (CCT) algorithm, a new scheduling algorithm for both sequential and parallel discrete event simulation. CCT is a general conservative algorithm that is aimed at th...
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This paper introduces the Critical Channel Traversing (CCT) algorithm, a new scheduling algorithm for both sequential and parallel discrete event simulation. CCT is a general conservative algorithm that is aimed at the simulation of low-granularity network models on shared-memory multi-processor computers. An implementation of the CCT algorithm within a kernel called TasKit has demonstrated excellent performance for large ATM network simulations when compared to previous sequential, optimistic and conservative kernels. TasKit has achieved two to three times speedup on a single processor with respect to a splay tree central-event-list based sequential kernel. On a 16 processor (R8000) Silicon Graphics PowerChallenge, TasKit has achieved an event-rate of 1.2 million events per second and a speedup of 26 relative to the sequential kernel for a large ATM network model. Performance is achieved through a multi-level scheduling scheme that supports the scheduling of large grains of computation even with low-granularity events. Performance is also enhanced by supporting good cache behavior and automatic load balancing. The paper describes the algorithm and its motivation, proves its correctness and briefly presents performance results for TasKit.
The High Level Architecture (HLA) provides the specification of a software architecture for distributedsimulation. The baseline definition of the HLA includes the HLA Rules, The HLA Interface Specification, and the H...
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The High Level Architecture (HLA) provides the specification of a software architecture for distributedsimulation. The baseline definition of the HLA includes the HLA Rules, The HLA Interface Specification, and the HLA Object Model Template. The HLA Rules are a set of 10 basic rules that define the responsibilities and relationships among the components of an HLA federation. The HLA Interface Specification provides a specification of the functional interfaces between HLA federates and the HLA Runtime Infrastructure. The HLA OMT provides a common presentation format for HLA simulation and Federation Object Models. The HLA was developed over the past three years. It is in the process of being applied with simulations developed for analysis, training and test and evaluation and incorporated into industry standards for distributedsimulation by both the Object Management Group and the IEEE. This paper provides a discussion of key areas where there are technology challenges in the future implementation and application of the HLA.
This paper presents a checkpointing scheme for optimistic simulation which is a mixed approach between periodic and probabilistic checkpointing. The latter based on statistical data collected during the simulation, ai...
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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 based 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.
A code for the simulation of X-ray diffraction pattern of a powder has been implemented on a massively parallel SIMD platform developed in the frame of the PQE2000 Project. The code allows the evaluation of the diffra...
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A code for the simulation of X-ray diffraction pattern of a powder has been implemented on a massively parallel SIMD platform developed in the frame of the PQE2000 Project. The code allows the evaluation of the diffraction pattern of atomic-scale models of both perfectly ordered and disordered structures. The code has been used to investigate the structures resulting from the non-equilibrium alloying process of an immiscible metallic couple (Ag-Cu).
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