Real-time multiprocessor locks with nesting: optimizing the common case

Nemitz, Catherine E.; Amert, Tanya; Anderson, James H.

doi:10.1007/s11241-019-09328-w

Cited by 9 publications

(5 citation statements)

References 41 publications

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“…R/W LLAB with other multi-resource locks, namely, DGL ( Ward and Anderson, 2013 ), R/W DGL (our task-fair reader–writer variant of DGL), R/W RNLP ( Ward and Anderson, 2014 ), MRLock ( Zhang et al, 2013 ), and a multi-bit test and test-and-set (TATAS) lock. The implementation of DGL uses a single queue and is obtained from Nemitz et al (2019a) . A fast-path optimization allows non-conflicting requests to bypass the queue 11 .…”

Section: Discussionmentioning

confidence: 99%

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Formal Verification of Real-Time Autonomous Robots: An Interdisciplinary Approach

Foughali

Zuepke

2022

Front. Robot. AI

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Due to the severe consequences of their possible failure, robotic systems must be rigorously verified as to guarantee that their behavior is correct and safe. Such verification, carried out on a model, needs to cover various behavioral properties (e.g., safety and liveness), but also, given the timing constraints of robotic missions, real-time properties (e.g., schedulability and bounded response). In addition, in order to obtain valid and useful verification results, the model must faithfully represent the underlying robotic system and should therefore take into account all possible behaviors of the robotic software under the actual hardware and OS constraints (e.g., the scheduling policy and the number of cores). These requirements put the rigorous verification of robotic systems at the intersection of at least three communities: the robotic community, the formal methods community, and the real-time systems community. Verifying robotic systems is thus a complex, interdisciplinary task that involves a number of disciplines/techniques (e.g., model checking, schedulability analysis, component-based design) and faces a number of challenges (e.g., formalization, automation, scalability). For instance, the use of formal verification (formal methods community) is hindered by the state-space explosion problem, whereas schedulability analysis (real-time systems) is not suitable for behavioral properties. Moreover, current real-time implementations of robotic software are limited in terms of predictability and efficiency, leading to, e.g., unnecessary latencies. This is flagrant, in particular, at the level of locking protocols in robotic software. Such situation may benefit from major theoretical and practical findings of the real-time systems community. In this paper, we propose an interdisciplinary approach that, by joining forces of the different communities, provides a scalable and unified means to efficiently implement and rigorously verify real-time robots. First, we propose a scalable two-step verification solution that combines formal methods and schedulability analysis to verify both behavioral and real-time properties. Second, we devise a new multi-resource locking mechanism that is efficient, predictable, and suitable for real-time robots and show how it improves the latter’s real-time behavior. In both cases, we show, using a real drone example, how our approach compares favorably to that in the literature. This paper is a major extension of the RTCSA 2020 publication “A Two-Step Hybrid Approach for Verifying Real-Time Robotic Systems.”

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Section: Discussionmentioning

confidence: 99%

“…To the best of our knowledge, R/W RNLP and fast R/W RNLP are the only real-time reader–writer multi-resource locks described in the literature ( Ward and Anderson, 2014 ; Nemitz et al, 2019a ). R/W RNLP provides phase fairness .…”

Section: Setting the Requirements For Real-time Locking In Roboticsmentioning

confidence: 99%

Formal Verification of Real-Time Autonomous Robots: An Interdisciplinary Approach

Foughali

Zuepke

2022

Front. Robot. AI

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“…Once the task assignment is done then the problem is converted to a uniprocessor (Günzel and Chen, 2020).In partitioned tasks mapped to dedicated processing nodes in many to one relationship. Set of tasks assigned to dedicated nodes as shown in Figure 3 (Gandhi et al, 2020) In global scheduling, tasks are maintained in the common tasks queue as shown in Figure 4 and assigned to distribute processing nodes and allowed to migrate among the distributed nodes to achieve load balancing (Nemitz et al, 2019).…”

Section: Partitioned Schedulermentioning

confidence: 99%

Cluster Based Real Time Scheduling for Distributed System

Talmale¹,

Shrawankar²

2021

ADCAIJ

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Real time tasks scheduling on a distributed system is a complex problem. The existing real time tasks scheduling techniques are primarily based on partitioned and global scheduling. In partitioned based scheduling the tasks are assigned on a dedicated processor. The advantages of partitioned based approach is existing uni-processor scheduling techniques can be used; no migration overheads but task assignment is NP hard problem and optimal utilization of processing nodes is not possible. In global scheduling all tasks are maintained in a single tasks queue and allocated to multiple processing nodes. The advantage of global scheduling is optimal utilization of processing nodes but suffer from high migration and preemption overheads. This paper proposed cluster based real time tasks scheduling on a distributed system which is a hybrid scheduling approach where processing nodes group into cluster and scheduling using global scheduling. The simulation result shows that the proposed scheduling increases the tasks acceptance ratio, resource utilization as compared to partitioned and global scheduling and reduces migration as well as preemption overheads.

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“…Ward and Anderson [25], [26] propose a "pluggable" protocol to support unrestricted lock nesting while guaranteeing asymptotically optimal priorityinversion blocking bounds. Their work was later extended by Nemitz et al [27] ensuring that both nested and nonnested requests are processed efficiently.…”

Section: Related Workmentioning

confidence: 99%

Precise Worst-Case Blocking Time of Tasks Under Priority Inheritance Protocol

Faldella

Loreti

2021

IEEE Trans. Comput.

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The problem of precisely computing the worst-case blocking time that tasks may experience is one of the fundamental issues of schedulability analysis of real-time applications. While exact methods have been proposed for more sophisticated protocols, the problem is indeed complex in case of the Priority Inheritance Protocol, even restricting the attention to uniprocessor systems, non-nested resource accesses, and non-self-suspending tasks. Besides a very simple method leading in general to loose upper bounds, only one algorithm of exponential complexity has been so far reported in literature to tighten such bounds. In this work, we describe a novel approach which, leveraging an operational research technique for modeling the problem, computes the same tight bounds in polynomial time. We then discuss the scenarios in which, assuming no conditional statements in the tasks' code, the computed bounds derive from an actually impossible blocking chain, and we refine the initial model to more precisely compute the worst-case blocking times for any task set in any possible operating condition.

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Real-time multiprocessor locks with nesting: optimizing the common case

Cited by 9 publications

References 41 publications

Formal Verification of Real-Time Autonomous Robots: An Interdisciplinary Approach

Formal Verification of Real-Time Autonomous Robots: An Interdisciplinary Approach

Cluster Based Real Time Scheduling for Distributed System

Precise Worst-Case Blocking Time of Tasks Under Priority Inheritance Protocol

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