| 1. |
- Desai, Nitin, 1986-, et al.
(författare)
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A Topology-specific Tight Worst-case Analysis of Strict Priority Traffic in Real-time Systems
- 2023
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Ingår i: IEEE Int. Conf. Emerging Technol. Factory Autom., ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9798350339918
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Konferensbidrag (refereegranskat)abstract
- Tight end-to-end worst-case delay bounds for periodic traffic streams are essential for time sensitive networks. In this paper, we provide an algorithm to compute a tight (and accurate) end-to-end worst-case bound by considering distinct topological patterns and the manner in which streams enter and leave switches. This refined analysis uses non-preemptive, strict-priority arbitration mechanism commonly deployed in Ethernet switches. Compared to the state-of-the-art that considers all higher and equal priority interference as contributing to the worst-case bound, we present an analytical approach for computing a tighter worst-case delay bound and prove through discrete event simulations that only a certain number of equal-priority interference streams can actually affect the worst-case case. Our results enable efficient resource allocation and have implications for online re-configuration mechanisms for time-sensitive factory communication systems.
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| 2. |
- Desai, Nitin, 1986-
(författare)
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Designing safe and adaptive time-critical fog-based systems
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Safety-critical systems in industrial automation, avionics, or automotive domains demand correct, timely and predictable performance under all(including faulty) operating conditions. Fault-tolerance plays an important role in ensuring seamless system function even in the presence of failures. Typically such systems run hard real-time applications, and hence timing violations can result in hazards. Fog computing is an adaptive paradigm which distributes computation and communication along the cloud-IoT continuum to reduce communication latencies, making it more conducive to execute real-time applications. This requires enhancements to the network connecting various sub-systems to support timely delivery of safety-critical messages. Traditionally safety-critical systems are designed offline and are not re-configured during runtime. The inherent adaptive properties of fog computing systems make it susceptible to timeliness violations and can be a hindrance to safety guarantees. At the same time, adaptivity in terms of migrating computation and communication to different devices in the fog-cloud continuum can be used to make the system more fault-tolerant by suitable design approaches. In this work we provide design approaches geared towards achieving safety and predictability of critical applications that run on adaptive fog computing platforms. To this end, we start by performing a survey of safety considerations in a fog computing system and identifying key safety challenges. We then propose a design approach to improve predictability in an autonomous mobile robot use-case in a factory setting designed using the fog computing paradigm. We narrow our attention on time-sensitive networking (TSN) and propose a temporal redundancy-based fault tolerance approach for time-sensitive messages. Furthermore, we study the 802.1CB TSN protocol and suggest improvements to reduce network congestion owing to replicated frames.As a future work, we intend to also include the wireless aspects in the evaluation of timeliness guarantees for safety-critical applications. The emphasis will be on run-time failure scenarios and self-healing mechanisms based on online decisions taken in concert with offline guarantees.
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| 3. |
- Desai, Nitin, 1986-, et al.
(författare)
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MALOC : Building an adaptive scheduling and routing framework for rate-constrained TSN traffic
- 2022
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Ingår i: IEEE International Conference on Emerging Technologies and Factory Automation, ETFA. - : Institute of Electrical and Electronics Engineers Inc.. - 9781665499965
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Konferensbidrag (refereegranskat)abstract
- Time Sensitive Networking (TSN) is a set of standards aimed at providing real-time guarantees over existing Ethernet standards. Worst-case traversal time (WCTT) analyses of network traffic are traditionally used in schedulability and routing analyses to determine feasible routes for traffic streams. However, worst-case conditions happen quite rarely from a probabilistic perspective. The typical or average-case traversal times are easier to compute and can be used as an effective design tool for routing and scheduling. In this paper, we present "MaLoC"or Maximally Loaded Common links for routing and scheduling of rate-constrained (RC) traffic in time-sensitive networks (TSN). The proposed framework employs a fully decentralized approach to route and schedule generation with only switch-local information. We further provide a preliminary evaluation of the proposed approach using a simple network topology.
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| 4. |
- Markovic, Filip, et al.
(författare)
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Cache-aware response time analysis for real-time tasks with fixed preemption points
- 2020
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Ingår i: The 26TH IEEE Real-time and embedded Technology and Applications Symposium RTAS'20. - Sydney, Australia : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 30-42
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In real-time systems that employ preemptive scheduling and cache architecture, it is essential to account as precisely as possible for cache-related preemption delays in the schedulability analysis, as an imprecise estimation may falsely deem the system unschedulable. In the current state of the art for preemptive scheduling of tasks with fixed preemption points, the existing schedulability analysis considers overly pessimistic estimation of cache-related preemption delay, which eventually leads to overly pessimistic schedulability results. In this paper, we propose a novel response time analysis for real-time tasks with fixed preemption points, accounting for a more precise estimation of cache-related preemption delays. The evaluation shows that the proposed analysis significantly dominates the existing approach by being able to always identify more schedulable tasksets.
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| 5. |
- Markovic, Filip, et al.
(författare)
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Improving the accuracy of cache-aware response time analysis using preemption partitioning
- 2020
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Ingår i: Leibniz International Proceedings in Informatics, LIPIcs. - 9783959771528
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Konferensbidrag (refereegranskat)abstract
- Schedulability analyses for preemptive real-time systems need to take into account cache-related preemption delays (CRPD) caused by preemptions between the tasks. The estimation of the CRPD values must be sound, i.e. it must not be lower than the worst-case CRPD that may occur at runtime, but also should minimise the pessimism of estimation. The existing methods over-approximate the computed CRPD upper bounds by accounting for multiple preemption combinations which cannot occur simultaneously during runtime. This over-approximation may further lead to the over-approximation of the worst-case response times of the tasks, and therefore a false-negative estimation of the system’s schedulability. In this paper, we propose a more precise cache-aware response time analysis for sporadic real-time systems under fully-preemptive fixed priority scheduling. The evaluation shows a significant improvement over the existing state of the art approaches.
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| 6. |
- Marković, Filip, 1992-
(författare)
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Preemption-Delay Aware Schedulability Analysis of Real-Time Systems
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Schedulability analysis of real-time systems under preemptive scheduling may often lead to false-negative results, deeming a schedulable taskset being unschedulable. This is the case due to the inherent over-approximation of many time-related parameters such as task execution time, system delays, etc., but also, in the context of preemptive scheduling, a significant over-approximation arises from accounting for task preemptions and corresponding preemption-related delays. To reduce false-negative schedulability results, it is highly important to as accurately as possible approximate preemption-related delays. Also, it is important to obtain safe approximations, which means that compared to the approximated delay, no higher corresponding delay can occur at runtime since such case may lead to false-positive schedulability results that can critically impact the analysed system. Therefore, the overall goal of this thesis is:To improve the accuracy of schedulability analyses to identify schedulable tasksets in real-time systems under fixed-priority preemptive scheduling, by accounting for tight and safe approximations of preemption-related delays.We contribute to the domain of timing analysis for single-core real-time systems under preemptive scheduling by proposing two novel cache-aware schedulability analyses: one for fully-preemptive tasks, and one for tasks with fixed preemption points. Also, we propose a novel method for deriving safe and tight upper bounds on cache-related preemption delay of tasks with fixed preemption points. Finally, we contribute to the domain of multi-core partitioned hard real-time systems by proposing a novel partitioning criterion for worst-fit decreasing partitioning, and by investigating the effectiveness of different partitioning strategies to provide task allocation which does not jeopardize the schedulability of a taskset in the context of preemptive~scheduling.
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| 7. |
- Stavrakakis, Ioannis, et al.
(författare)
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The teaching of computer ethics on computer science and related degree programmes. a European survey
- 2021
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Ingår i: INTERNATIONAL JOURNAL OF ETHICS EDUCATION. - : Springer Science and Business Media LLC. - 2364-0006 .- 2363-9997. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Within the Computer Science community, many ethical issues have emerged as significant and critical concerns. Computer ethics is an academic field in its own right and there are unique ethical issues associated with information technology. It encompasses a range of issues and concerns including privacy and agency around personal information, Artificial Intelligence and pervasive technology, the Internet of Things and surveillance applications. As computing technology impacts society at an ever growing pace, there are growing calls for more computer ethics content to be included in Computer Science curricula. In this paper we present the results of a survey that polled faculty from Computer Science and related disciplines about teaching practices for computer ethics at their institutions. The survey was completed by respondents from 61 universities across 23 European countries. Participants were surveyed on whether or not computer ethics is taught to Computer Science students at each institution, the reasons why computer ethics is or is not taught, how computer ethics is taught, the background of staff who teach computer ethics and the scope of computer ethics curricula. This paper presents and discusses the results of the survey.
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