Real-time distributedsimulations, such as on-line gaming or military training simulations are normally considered to be non-deterministic. Analysis of these simulations is therefore difficult depending solely on logg...
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ISBN:
(纸本)0769506771
Real-time distributedsimulations, such as on-line gaming or military training simulations are normally considered to be non-deterministic. Analysis of these simulations is therefore difficult depending solely on logging and runtime observations. This paper explores art approach for removing one major source of nondeterminism in these simulations, thereby allowing repeatable executions. Specifically, we use a synchronization protocol to ensure repeatable delivery of messages. Through limited instrumentation of the simulation code, we maintain a virtual time clock, by which message delivery! is governed. The additional overhead imposed by the scheme is shown to be reasonable, although additional reductions in this overhead are anticipated The results are demonstrated in the context of a simple combat model whose only source of non-determinism is communications latency. The simulation is shown to be tirade repeatable, and the perturbation on the execution compared to the nonrepeatable execution small. The paper is one step in bridging the gap between the traditional PDES perspective and real-time simulation world.
The simulation of wide area computer networks is one area where the benefits of parallelsimulation have been clearly demonstrated Here we present a description of a system that uses a parallel discrete event simulato...
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ISBN:
(纸本)0769506771
The simulation of wide area computer networks is one area where the benefits of parallelsimulation have been clearly demonstrated Here we present a description of a system that uses a parallel discrete event simulator to act as a high speed network emulator With this, real Internet Protocol (IP) traffic generated by application programs running on user workstations can interact with modelled traffic in the emulator thus providing a controlled test environment for distributed applications. The network emulator uses the TasKit conservative parallel discrete event simulation (PDES) kernel. TasKit has been shown to be able to achieve improved parallel performance over existing conservative and optimistic PDES kernels, as well as improved sequential performance over an existing central-event-list based kernel. This paper explains the modifications that have been made to TasKit to enable real-time operation along with the emulator interface that allows the IP network simulation running in the TasKit kernel to interact with real IP clients. Initial emulator performance data is included.
In a large-scale distributedsimulation with thousands of dynamic objects, efficient communication of data among these objects is an important issue. The broadcasting mechanism specified by the distributed Interactive...
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ISBN:
(纸本)0769506771
In a large-scale distributedsimulation with thousands of dynamic objects, efficient communication of data among these objects is an important issue. The broadcasting mechanism specified by the distributed Interactive simulation (DIS) standards is not suitable for large scale described simulation. In the High Level Architecture (HLA) paradigm, the Runtime Infrastructure (RTI) provides a set of services, sich as data distribution management (DDM) among federates. The goal of the DDM module in RTI is to make the data communication more efficient by sending the data only to those federates that need the data, as opposed to the broadcasting mechanism employed by DIS. Several DDM schemes have appeared in the literature. In this paper we discuss grid-based DDM and develop a DDM model that uses grids for matching the publishing/subscription regions, and for data filtering. We show that appropriate choice of the grid-cell size is crucial in obtaining good performance. We develop an analytical model and derive a formula for identifying the optimal cell size in grid-based DDM.
This paper visits issues that recur in consideration of simulation time-stamps, in the context of building very large simulation models from components developed by different groups, at different times. A key problem ...
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ISBN:
(纸本)0769506771
This paper visits issues that recur in consideration of simulation time-stamps, in the context of building very large simulation models from components developed by different groups, at different times. A key problem here is "safety", loosely defined to mean that unintended model behavior does not occur due to unpredictable behavior of timestamp generation and comparisons. We revisit the problems of timestamp format and simultaneity, and then turn to the new problem of timestamp inter-operability. We describe how a C++ simulation kernel can support the concurrent evaluation of submodels that internally use heterogeneous timestamps, and evaluate the execution time costs of doing so. We find that use of a safe timestamp format that explicitly allows different timescales costs less than 10 over a stock 64-bit integer format, whereas support for completely heterogeneous timestamps can cost as much as 50% in execution speed.
Several scheduling algorithms have been proposed to determine the ne,rr event to be executed on a processor in a Time Warp parallel discrete event simulation. However none of them is specifically designed for simulati...
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ISBN:
(纸本)0769506771
Several scheduling algorithms have been proposed to determine the ne,rr event to be executed on a processor in a Time Warp parallel discrete event simulation. However none of them is specifically designed for simulations where the execution time (or granularity)for different ty,pes of events has large variance. In this paper we present a grain sensitive scheduling algorithm which addresses this problem. In our solution, the scheduling decision depends on both timestamp and granularity values with the aim at giving higher priority, to small grain events even if their timestamp is not the lowest one (i.e. the closest one to the commitment horizon of the simulation). This implicitly limits the optimism of the execution of large grain events that, if rolled back, would produce large waste of CPU time. The algorithm is adaptive in that it relies on the dynamic recalculation of the length of a simulated time window within which the timestamp of ally good candidate event for the scheduling falls in. if the window length is set to Zeta, then the algorithm behaves like the standard Lowest-Timestamp-First (LTF) scheduling algorithm. simulation results of a classical benchmark in several different configurations are reported for a performance comparison with LTE These results demonstrate the effectiveness of our algorithm.
The concept of strong groups is introduced to describe the structure of simulation models. It is shown that logical processes within strong groups process at approximately the same rate and that different strong group...
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The concept of strong groups is introduced to describe the structure of simulation models. It is shown that logical processes within strong groups process at approximately the same rate and that different strong groups can progress at different rates. An algorithm based on the rates of the strong groups is presented to balance the load among the physical processors and for flow control.
In this paper we examine various modeling and simulation applications of cluster computing using a Beowulf cluster. Those applications are used to investigate the performance of our cluster in terms of computational s...
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ISBN:
(纸本)0769508375
In this paper we examine various modeling and simulation applications of cluster computing using a Beowulf cluster. Those applications are used to investigate the performance of our cluster in terms of computational speedup, scalability, and communications. The applications include solution of linear systems by Jacobi iteration, distributed image gent ration, and the finite difference time domain solution of Maxwell's equations. It is observed that the computational load for these applications must be large compared to the communication overhead tr, take advantage of the speedup obtained using parallel computing. For the applications reviewed here, this condition is increasingly satisfied as the problem size becomes larger or as higher resolution is required.
It is well known that the critical path provides an absolute lower bound on the execution time of a conservative parallel discrete event simulation. It stands to reason that optimal execution time can only be achieved...
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It is well known that the critical path provides an absolute lower bound on the execution time of a conservative parallel discrete event simulation. It stands to reason that optimal execution time can only be achieved by immediately executing each event on the critical path. However, dynamically identifying the critical event is difficult, if not impossible. In this paper, we examine several heuristics that might help to determine the critical event, and conduct a performance study to determine the effectiveness of using these heuristics for preferential scheduling.
In this paper we describe an approach to exploit temporal uncertainty in parallel and distributedsimulation by utilizing time intervals rather than precise time stamps. Unlike previously published work that propose n...
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In this paper we describe an approach to exploit temporal uncertainty in parallel and distributedsimulation by utilizing time intervals rather than precise time stamps. Unlike previously published work that propose new message ordering semantics, our approach is based on conservative, time stamp order execution and enhancing the lookahead of the simulation by pre-drawing random numbers from a distribution that models temporal uncertainty. The advantages of this approach are that it allows time intervals to be exploited using a conventional Time Stamp Order (TSO) delivery mechanism, and it offers the modeler greater statistical control over the assigned time stamps. An implementation of this approach is described and initial performance measurements are presented.
Performance models exist that reliably describe the execution time and efficiency of parallel discrete-event simulations executed in a synchronous iterative fashion. These performance models incorporate the effects of...
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Performance models exist that reliably describe the execution time and efficiency of parallel discrete-event simulations executed in a synchronous iterative fashion. These performance models incorporate the effects of processor heterogeneity, other processor load due to shared computational resources, application workload imbalance, and the use of speculative computation. This includes modeling the effects of predictive optimism, a technique for improving the accuracy of speculative assumptions. We extend these models to incorporate correlated workloads across the set of processors and validate the models with two different applications.
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