| 1. |
- Friebe, Anna, et al.
(författare)
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Identification and validation of markov models with continuous emission distributions for execution times
- 2020
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Ingår i: 2020 IEEE 26th International Conference on Embedded and Real-Time Computing Systems and Applications, RTCSA 2020. - : Institute of Electrical and Electronics Engineers Inc.. - 9781728144030
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Konferensbidrag (refereegranskat)abstract
- It has been shown that in some robotic applications, where the execution times cannot be assumed to be independent and identically distributed, a Markov Chain with discrete emission distributions can be an appropriate model. In this paper we investigate whether execution times can be modeled as a Markov Chain with continuous Gaussian emission distributions. The main advantage of this approach is that the concept of distance is naturally incorporated. We propose a framework based on Hidden Markov Model (HMM) methods that 1) identifies the number of states in the Markov Model from observations and fits the Markov Model to observations, and 2) validates the proposed model with respect to observations. Specifically, we apply a tree-based cross-validation approach to automatically find a suitable number of states in the Markov model. The estimated models are validated against observations, using a data consistency approach based on log likelihood distributions under the proposed model. The framework is evaluated using two test cases executed on a Raspberry Pi Model 3B+ single-board computer running Arch Linux ARM patched with PREEMPT_RT. The first is a simple test program where execution times intentionally vary according to a Markov model, and the second is a video decompression using the ffmpeg program. The results show that in these cases the framework identifies Markov Chains with Gaussian emission distributions that are valid models with respect to the observations.
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| 2. |
- Friebe, Anna, et al.
(författare)
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Work-in-progress : Validation of probabilistic timing models of a periodic task with interference - A case study
- 2019
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Ingår i: Proceedings - Real-Time Systems Symposium. - : Institute of Electrical and Electronics Engineers Inc.. - 9781728144030 ; , s. 524-527
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Konferensbidrag (refereegranskat)abstract
- Probabilistic timing analysis techniques have been proposed for real-time systems to remedy the problems that deterministic estimates of the task's Worst-Case Execution Time and Worst-Case Response-Time can be both intractable and overly pessimistic. Often, assumptions are made that a task's response time and execution time probability distributions are independent of the other tasks. This assumption may not hold in real systems. In this paper, we analyze the timing behavior of a simple periodic task on a Raspberry Pi model 3 running Arch Linux ARM. In particular, we observe and analyze the distributions of wake-up latencies and execution times for the sequential jobs released by a simple periodic task. We observe that the timing behavior of jobs is affected by release events during the job's execution time, and of other processes running in between subsequent jobs of the periodic task. Using a data consistency approach we investigate whether it is reasonable to model the timing distribution of jobs affected by release events and intermediate processes as translations of the empirical timing distribution of non-affected jobs. According to the analysis, this paper shows that a translated distribution model of non-affected jobs is invalid for the execution time distribution of jobs affected by intermediate processes. Regarding the wake-up latency distribution with intermediate processes, a translated distribution model is improbable, but cannot be completely ruled out.
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| 3. |
- Houtan, Bahar, et al.
(författare)
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Work in progress : Investigating the effects of high priority traffic on the best effort traffic in TSN networks
- 2019
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Ingår i: Proceedings - Real-Time Systems Symposium. - : Institute of Electrical and Electronics Engineers Inc.. - 9781728144030 ; , s. 556-559
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the effects of various parameters of high priority traffic classes on the Best Effort (BE) traffic in the networks based on the IEEE Time Sensitive Networking (TSN) standards. In this regard, the paper discusses ongoing work and presents preliminary results using a TSN simulator. The results indicate that several parameters of the high priority traffic such as periods, offsets and preemption modes can have a significant impact on the quality of service (e.g., guaranteed message delivery and message delays) of the BE traffic.
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| 4. |
- Natarajan, Saranya, et al.
(författare)
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From Code to Weakly Hard Constraints : A Pragmatic End-to-End Toolchain for Timed C
- 2019
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Ingår i: Proceedings - Real-Time Systems Symposium. - : Institute of Electrical and Electronics Engineers Inc.. - 9781728144030 ; , s. 167-180
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Konferensbidrag (refereegranskat)abstract
- Complex real-time systems are traditionally developed in several disjoint steps: (i) decomposition of applications into sets of recurrent tasks, (ii) worst-case execution time estimation, and (iii) schedulability analysis. Each step is already in itself complex and error-prone, and the composition of all three poses a nontrivial integration problem. In particular, it is challenging to obtain an end-to-end analysis of timing properties of the whole system due to practical differences between the interfaces of tools for extracting task models, execution time analysis, and schedulability tests. To address this problem, we propose a seamless and pragmatic end-to-end compilation and timing analysis toolchain, where source programs are written in a real-time extension of C, called Timed C. The toolchain automatically translates timing primitives into executable code, measures execution times, and verifies temporal correctness using an extended schedulability test for non-preemptive generalized multiframe task sets. Novel aspects of our approach are: (i) both soft and firm tasks can be expressed at the programming language level and stated timing requirements are automatically verified by the schedulability test, and (ii) the schedulability test outputs per-job response-time information that enables a new approach to sensitivity analysis. Specifically, we perform a weakly hard sensitivity analysis that determines the worst-case execution time margins for the strongest still-satisfied (M,K) constraint, where M = m1 +...+ mN denotes the number of deadline misses across the entire task set, and K = {k1,..., kN} is the set of windows of interest of the different tasks. The toolchain is implemented as a source-to-source compiler, freely available as open source, and conveniently distributed as a Docker container.
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