ACM Transactions on Modeling and Computer Simulation最新文献

The examined paper introduces a parallel version of SeQUeNCe, a Discrete Event Simulator for quantum networks. The authors have deposited their artifact on Zenodo, meeting the criteria for long-term preservation required by the Artifacts Available badge. The software within the artifact functions correctly with minor adjustments, aligning with the paper’s relevance and earning the Artifacts Evaluated—Functional badge. Additionally, due to the reasonable quality and customizability of the artifact, the Artifacts Evaluated—Reusable badge has also been awarded. The authors didn’t request the Artifacts Evaluated—Reproduced badge and they did not include the scripts used to generate and display their experimental results. As a result, it has not been possible to replicate the results published in their paper.

Shared-memory multi-processor/multi-core machines have become a reference for many application contexts. In particular, the recent literature on speculative parallel discrete event simulation has reshuffled the architectural organization of simulation systems in order to deeply exploit the main features of this type of machines. A core aspect dealt with has been the full sharing of the workload at the level of individual simulation events, which enables keeping the rollback incidence minimal. However, making each worker thread continuously switch its execution between events destined to different simulation objects does not favor locality. This problem appears even more evident in the case of Non-Uniform-Memory-Access (NUMA) machines, where memory accesses generating a cache miss to be served by a far NUMA node give rise to both higher latency and higher traffic at the level of the NUMA interconnection. In this article, we propose a workload-sharing algorithm where the worker threads can have short-term binding with specific simulation objects to favor spatial locality. The new bindings—carried out when a thread decides to switch its execution to other simulation objects—are based on both (a) the timeline according to which the object states have passed through the caching hierarchy and (b) the (dynamic) placement of objects within the NUMA architecture. At the same time, our solution still enables the worker threads to focus their activities on the events to be processed whose timestamps are closer to the simulation commit horizon—hence we exploit temporal locality along virtual time and keep the rollback incidence minimal. In our design we exploit lock-free constructs to support scalable thread synchronization while accessing the shared event pool. Furthermore, we exploit a multi-view approach of the event pool content, which additionally favors local accesses to the parts of the event pool that are currently relevant for the thread activity. Our solution has been released as an integration within the USE (Ultimate-Share-Everything) open source speculative simulation platform available to the community. Furthermore, in this article we report the results of an experimental study that shows the effectiveness of our proposal.

A digital twin contains up-to-date data-driven models of the physical world being studied and can use simulation to optimise the physical world. However, the analysis made by the digital twin is valid and reliable only when the model is equivalent to the physical world. Maintaining such an equivalent model is challenging, especially when the physical systems being modelled are intelligent and autonomous. The paper focuses in particular on digital twin models of intelligent systems where the systems are knowledge-aware but with limited capability. The digital twin improves the acting of the physical system at a meta-level by accumulating more knowledge in the simulated environment. The modelling of such an intelligent physical system requires replicating the knowledge-awareness capability in the virtual space. Novel equivalence maintaining techniques are needed, especially in synchronising the knowledge between the model and the physical system. This paper proposes the notion of knowledge equivalence and an equivalence maintaining approach by knowledge comparison and updates. A quantitative analysis of the proposed approach confirms that compared to state equivalence, knowledge equivalence maintenance can tolerate deviation thus reducing unnecessary updates and achieve more Pareto efficient solutions for the trade-off between update overhead and simulation reliability.

Network emulation allows unmodified code execution on lightweight containers to enable accurate and scalable networked application testing. However, such testbeds cannot guarantee fidelity under high workloads, especially when many processes concurrently request resources (e.g., CPU, disk I/O, GPU, and network bandwidth) that are more than the underlying physical machine can offer. A virtual time system enables the emulated hosts to maintain their own notion of virtual time. A container can stop advancing its time when not running (e.g., in an idle or suspended state). The existing virtual time systems focus on precise time management for CPU-intensive applications but are not designed to handle other operations, such as disk I/O, network I/O, and GPU computation. In this paper, we develop a lightweight virtual time system that integrates precise I/O time for container-based network emulation. We model and analyze the temporal error during I/O operations and develop a barrier-based time compensation mechanism in the Linux kernel. We also design and implement Dynamic Load Monitor (DLM) to mitigate the temporal error during I/O resource contention. VT-IO enables accurate virtual time advancement with precise I/O time measurement and compensation. The experimental results demonstrate a significant improvement in temporal error with the introduction of DLM. The temporal error is reduced from 7.889 seconds to 0.074 seconds when utilizing the DLM in the virtual time system. Remarkably, this improvement is achieved with an overall overhead of only 1.36% of the total execution time.

Layered queueing networks (LQNs) are an extension of ordinary queueing networks useful to model simultaneous resource possession and stochastic call graphs in distributed systems. Existing computational algorithms for LQNs have primarily focused on mean-value analysis. However, other solution paradigms, such as normalizing constant analysis and mean-field approximation, can improve the computation of LQN mean and transient performance metrics, state probabilities, and response time distributions. Motivated by this observation, we propose the first LQN meta-solver, called LN, that allows for the dynamic selection of the performance analysis paradigm to be iteratively applied to the submodels arising from layer decomposition. We report experiments where this added flexibility helps us to reduce the LQN solution errors. We also demonstrate that the meta-solver approach eases the integration of LQNs with other formalisms, such as caching models, enabling the analysis of more general classes of layered stochastic networks. Additionally, to support the accurate evaluation of the LQN submodels, we develop novel algorithms for homogeneous queueing networks consisting of an infinite server node and a set of identical queueing stations. In particular, we propose an exact method of moment algorithms, integration techniques for normalizing constants, and a fast non-iterative mean-value analysis technique.

In many real world problems, we are faced with the problem of selecting the best among a finite number of alternatives, where the best alternative is determined based on context specific information. In this work, we study the contextual Ranking and Selection problem under a finite-alternative-finite-context setting, where we aim to find the best alternative for each context. We use a separate Gaussian process to model the reward for each alternative, and derive the large deviations rate function for both the expected and worst-case contextual probability of correct selection. We propose the GP-C-OCBA sampling policy, which uses the Gaussian process posterior to iteratively allocate observations to maximize the rate function. We prove its consistency and show that it achieves the optimal convergence rate under the assumption of a non-informative prior. Numerical experiments show that our algorithm is highly competitive in terms of sampling efficiency, while having significantly smaller computational overhead.

Emergency and crisis simulations play a pivotal role in equipping authorities worldwide with the necessary tools to minimize the impact of catastrophic events. Various studies have explored the integration of intelligence into Multi-Agent Systems (MAS) for crisis simulation. This involves incorporating psychological behaviours from the social sciences and utilizing data-driven machine learning models with predictive capabilities. A recent advancement in behavioural modelling is the Conscious Movement Model (CMM), designed to modulate an agent’s movement patterns dynamically as the situation unfolds. Complementing this, the model incorporates a Conscious Movement Memory-Attention (CMMA) mechanism, enabling learnability through training on pedestrian trajectories extracted from video data. The CMMA facilitates mapping a pedestrian’s attention to their surroundings and understanding how their past decisions influence their subsequent actions. This study proposes an efficient framework that integrates the trained CMM into a simulation model specifically tailored for emergency evacuations, ensuring realistic outcomes. The resulting simulation framework automates strategy management and planning for diverse emergency evacuation scenarios. A single-objective method is presented for generating prescriptive analytics, offering effective strategy options based on predefined operational rules. To validate the framework’s efficacy, a case study of a theatre evacuation is conducted. In essence, this research establishes a robust simulation framework for crisis management, with a particular emphasis on modelling pedestrians during emergency evacuations. The framework generates prescriptive analytics to aid authorities in executing rescue and evacuation operations effectively.