The notion of temporal uncertainty, expressed as the possibility for an event to occur in an interval of simulation time, rather than at a specific instant, has been recently proposed and exploited in order to enhance...
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ISBN:
(纸本)0769521118
The notion of temporal uncertainty, expressed as the possibility for an event to occur in an interval of simulation time, rather than at a specific instant, has been recently proposed and exploited in order to enhance the performance of parallel/distributedsimulation systems. In this paper we propose the concept of "spatial uncertainty" expressed as the possibility for a simulation event to occur in one of a set of points within the simulated system space. How to handle/exploit space uncertain events in an optimistic simulation system is discussed. Also, experimental results for optimistic simulations of a Personal Communication System (PCS) modeled with space uncertain events are reported These results show the ability of spatial uncertainty to increase the performance of the parallelsimulation system by providing a more flexible approach to synchronization.
This paper advocates the use of a formal framework for analyzing simulation performance. simulation performance is characterized based on the three simulation development process boundaries: physical system, simulatio...
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ISBN:
(纸本)0769521118
This paper advocates the use of a formal framework for analyzing simulation performance. simulation performance is characterized based on the three simulation development process boundaries: physical system, simulation model, and simulator implementation. Firstly, we formalize simulation event ordering using partially ordered set theory. A simulator implements a simulation event ordering, and incurs implementation overheads when enforcing event ordering at runtime. Secondly, we apply our formalism to extract and formalize the simulation event orderings of both sequential and parallelsimulations. Thirdly, we propose the relation stricter and a measure called strictness for comparing and quantifying the degree of event dependency of simulation event orderings respectively.
Designing fast parallel discrete event simulation systems for shared-memory parallel computers is simplified by the efficient communication operations enabled by the common memory space. The difficulties involved in d...
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ISBN:
(纸本)0769521118
Designing fast parallel discrete event simulation systems for shared-memory parallel computers is simplified by the efficient communication operations enabled by the common memory space. The difficulties involved in designing large shared-memory computers and the resulting high cost of even modest size systems has led to the proliferation of computer systems consisting of small shared-memory computers connected via low-latency message-passing interconnection networks. This paper describes how a network simulation system using a simulation kernel optimized for high performance operation on shared-memory parallel computers has been extended to operate on computers that mix shared-memory and message-passing paradigms. Results are presented showing that the system can achieve over 60 million simulated packet transmissions per second on 32 4-processor nodes. The results demonstrate the advantage of using a mixture of shared-memory and message-passing over using only message-passing in many cases.
In optimistic simulations, checkpointing techniques are often used to reduce the overhead caused by state saving. In this paper, we propose event reconstruction as a technique with which to reduce the overhead caused ...
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ISBN:
(纸本)0769521118
In optimistic simulations, checkpointing techniques are often used to reduce the overhead caused by state saving. In this paper, we propose event reconstruction as a technique with which to reduce the overhead caused by event saving, and compare its memory consumption and execution time to the results obtained by dynamic checkpointing. As the name implies, event reconstruction reconstructs input events and anti-events from the differences between adjacent states, and does not save input events in the event queue. For simulations with fine event granularity and small state size, such as the logic simulation of VLSI circuitry, event reconstruction can yield an improvement in execution time as well as a significant reduction in memory utilization when compared to dynamic checkpointing. Moreover, this technique facilitates load migration because only the state queue needs to be moved from one processor to another.
We investigated the benefit of exploiting the symmetries of graphs for partitioning. We represent the model to be simulated by a weighted graph. Graph symmetries are studied in the theory of permutation groups and can...
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ISBN:
(纸本)0769521118
We investigated the benefit of exploiting the symmetries of graphs for partitioning. We represent the model to be simulated by a weighted graph. Graph symmetries are studied in the theory of permutation groups and can be calculated in polynomial time with the nauty algorithm [15]. We designed an algorithm to extract useful symmetries from the automorphism group, which can be used to create partitions derived from the graph's structure. Our approach is focused on composite graphs, for which identical subgraphs reoccur in the graph. If these identical subgraphs can be mapped onto each other by symmetries, the subgraphs are replaced by equivalent multivertices, resulting in a 'natural' aggregation of vertices. This approach is applied to parallelsimulation of a detailed IP-switch with a conservative synchronous algorithm. The experimental results show that even for good partitions, global and temporal load imbalances are inevitable.
In distributed wargame simulations, the states of simulation entities need to be updated and sent to other simulation nodes in a timely manner, which may incur high overhead on the network. Thus, how to efficiently us...
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ISBN:
(纸本)0769521118
In distributed wargame simulations, the states of simulation entities need to be updated and sent to other simulation nodes in a timely manner, which may incur high overhead on the network. Thus, how to efficiently use the limited bandwidth of the network is very important to the performance of distributed wargame simulations. In this paper, a utility model is proposed to evaluate the relative importance of a simulation entity. In our proposed utility model, the utility of an entity is determined by the number of entities on which this entity may have influence and the distances between this entity and the entities within its area of influence. Based on the utility model, we may devise some flexible updating mechanisms which can utilize the band-width more efficiently. For example, the state updates of an important entity which may have great influence on the simulation could be sent to other nodes with a high frequency;on the other hand, the state updates of an entity with little importance may be sent to other simulation nodes with a low frequency. In this paper, we will focus on the utility computation of a simulation entity rather than the flexible state updating mechanisms for the simulation entities. Our proposed utility computation mechanism is general and can be easily implemented using the HLA services. Experimental results show that the utility computation mechanism incurs little overhead.
In this work we focus on a new technique for making cloning of parallelsimulations more efficient. Cloning provides a means for running multiple similar simulations in parallel where many computations are shared rath...
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ISBN:
(纸本)0769521118
In this work we focus on a new technique for making cloning of parallelsimulations more efficient. Cloning provides a means for running multiple similar simulations in parallel where many computations are shared rather than repeated [12]. A simulation is cloned on an event for a particular set of logical processes, creating new LP clones. The clones diverge as messages from the new LPs arrive at uncloned LPs. Until replication, all the computations for a particular LP are shared between the clones. simulation kernels using cloning achieve efficiency by incrementally replicating logical processes as necessary. This enables regions of the simulation that have not been affected to use the same computations for both the new and old clone. Clearly, the longer replication can be delayed, the more efficient the simulation. We hypothesize that in many cases replication takes place before it is strictly necessary. We propose just-in-time cloning that addresses this issue by relaxing the constraints of simulation cloning to further benefit from shared computations.
We study the adaptation of an optimistic Time Warp kernel to cross-cluster computing on the Grid. Wide area communication, the primary source of overhead, is off-loaded onto dedicated routing processes. This allows th...
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ISBN:
(纸本)0769521118
We study the adaptation of an optimistic Time Warp kernel to cross-cluster computing on the Grid. Wide area communication, the primary source of overhead, is off-loaded onto dedicated routing processes. This allows the simulation processes to run at full speed and it thus significantly decreases the performance gap caused by the wide area distribution. Further improvements are obtained by employing message aggregation on the wide area links. We achieve many of our objectives for lazy cancellation and moderate communication, but high communication rates with aggressive cancellation remains a challenge.
Conservative parallel discrete event simulation takes a connection-oriented approach to inter-process communication. Conservative processes modeling physical entities are connected via channels that represent physical...
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ISBN:
(纸本)0769521118
Conservative parallel discrete event simulation takes a connection-oriented approach to inter-process communication. Conservative processes modeling physical entities are connected via channels that represent physical links in the target system. By contrast, optimistic strategy and its implementation in Time Warp machine, take a connectionless approach where a process can communicate freely with any other process without prior connection. This paper presents the case for a connection-oriented optimistic approach and provides a data structure for the event set of Time Warp processes that significantly reduces the cost of event scheduling and cancellation under connection-oriented operation. Detailed description of the proposed implementation is given and performance of the structure in forward event scheduling and backward event cancellation is tested and the results are discussed.
An important question for network simulation is what level of detail is required to obtain a desired level of accuracy. While in some networks, the level of detail is an open research issue (for example, radio propaga...
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ISBN:
(纸本)0769521118
An important question for network simulation is what level of detail is required to obtain a desired level of accuracy. While in some networks, the level of detail is an open research issue (for example, radio propagation models in wireless networks), it has long been assumed that wired networks could be accurately modeled by fairly simple queues with a bandwidth limit and propagation delay. To our knowledge this assumption has not been widely tested In this paper we evaluate different levels of detail for an Ethernet simulation. We consider two models for Ethernet simulation;a detailed, CSMA/CD protocol based model and a more abstract model using a DropTail, shared queue. Using web traffic with two different TCP simulation models, we evaluated the accuracy of these Ethernet models as compared to testbed measurements. We observed the DropTail Ethernet model requires significantly less execution time and can accurately model performance using a bandwidth normalization factor.
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