Feasible Automatic Reconfigurations of Real-Time OS Tasks

Gharsellaoui, Hamza; Gharbi, Atef; Khalgui, Mohamed; Ahmed, Samir Ben

doi:10.4018/978-1-4666-0294-6.ch017

Cited by 16 publications

(19 citation statements)

References 24 publications

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“…The software engineering principles for embedded system should address specific constraints such as hard timing constraints, limited memory and power use, predefined hardware platform technology, and hardware costs. On the other hand, the new generations of embedded control systems are adressing new criteria such as flexibility and agility (H. Gharsellaoui and BenAhmed, 2012). For these reasons, there is a need to develop tools, methodologies in embedded software engineering and dynamic reconfigurable embedded control sys-tems as an independent discipline.…”

Section: Introductionmentioning

confidence: 99%

An EDF-based Scheduling Algorithm for Real-time Reconfigurable Sporadic Tasks

Gharsellaoui¹,

Khalgui²,

Ahmed³

2013

Proceedings of the 8th International Joint Conference on Software Technologies

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This paper deals with the problem of scheduling the mixed workload of both homogeneous multiprocessor on-line sporadic and off-line periodic tasks in a hard reconfigurable real-time environment by an optimal EDF-based scheduling algorithm. Two forms of automatic reconfigurations which are assumed to be applied at run-time: Addition-Removal of tasks or just modifications of their temporal parameters: WCET and/or deadlines. Nevertheless, when such a scenario is applied to save the system at the occurrence of hardwaresoftware faults, or to improve its performance, some real-time properties can be violated at run-time. We define an Intelligent Agent that automatically checks the system's feasibility after any reconfiguration scenario to verify if all tasks meet the required deadlines after a reconfiguration scenario ψ h (h ∈ 1..M, we assume that we have M reconfiguration scenarios), was applied on a multiprocessor embedded system in the case of shared memory. Indeed, if the system is unfeasible, then the Intelligent Agent dynamically provides precious technical solutions for users to send sporadic tasks to idle times, by modifying the deadlines of tasks, the worst case execution times (WCETs), the activation time, by tolerating some non critical tasks m among n according to the (m,n) firm and a reasonable cost, by sending some tasks from their current processors to be scheduled in other processors, or in the worst case by removing some soft tasks according to predifined heuristic. We implement the agent to support these services in order to demonstrate the effectiveness and the excellent performance of the new optimal algorithm in normal and overload conditions.

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Section: Introductionmentioning

confidence: 99%

An EDF-based Scheduling Algorithm for Real-time Reconfigurable Sporadic Tasks

Gharsellaoui¹,

Khalgui²,

Ahmed³

2013

Proceedings of the 8th International Joint Conference on Software Technologies

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“…If time quantum is too large, the response time of the processes is too much which may not be tolerated in interactive environment. If time quantum is too small, it causes unnecessarily frequent context switch leading to more overheads resulting in less throughput [34]. T1 6 14 14 T2 3 14 14 T 3 4 14 14 Table 0.6: A task set example Figure 5.…”

Section: Round Robin (Rr) Algorithmmentioning

confidence: 99%

“…Since the run time is not defined, laxity changes continuously. The advantage of allowing high utilization is accompanied by a high computational effort at schedule time and poor overload performance [34]. …”

Section: Least Laxity First (Llf) Algorithmmentioning

confidence: 99%

“…Implicitly, if all processes can meet their deadlines for executions beginning at a critical instant, then they will always meet their deadlines. Thus, we have formed the basis for a schedulability test: check the executions of all processes for a single execution assuming that all processes are released simultaneously [34]. …”

Section: Rate Monotonic Algorithm (Rm Policy)mentioning

confidence: 99%

“…Consequently, the impact of software on the customer and, hence, on market shares and competition will be enormous. So, we can conclude that software is established as a key technology in the domain of real-time embedded systems (H.Gharsellaoui, M.Khalgui, S.BenAhmed, 2011) [34].…”

Section: Introductionmentioning

confidence: 99%

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New Optimal Solutions for Real-Time Reconfigurable Periodic Asynchronous OS Tasks with Minimizations of Response Times

Gharsellaoui

Gharbi

Mosbahi³

et al.

Embedded Computing Systems

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This research work deals with Reconfigurable Uniprocessor embedded Real-Time Systems to be classically implemented by different OS tasks that we suppose independent, asynchronous and periodic in order to meet functional and temporal properties described in user requirements. We define in the book chapter a schedulability algorithm for preemptable, asynchronous and periodic reconfigurable task systems with arbitrary relative deadlines, scheduled on a uniprocessor by an optimal scheduling algorithm based on the EDF principles and on the dynamic reconfiguration. Two forms of automatic reconfigurations which are assumed to be applied at run-time: Addition-Remove of tasks or just modifications of their temporal parameters: WCET and/or Periods. Nevertheless, when such a scenario is applied to save the system at the occurrence of hardwaresoftware faults, or to improve its performance, some real-time properties can be violated. We define a new semantic of the reconfiguration where a crucial criterion to consider is the automatic improvement of the system's feasibility at run-time by using an Intelligent Agent that automatically checks the system's feasibility after any reconfiguration scenario to verify if all tasks meet the required deadlines. Indeed, if a reconfiguration scenario is applied at run-time, then the Intelligent Agent dynamically provides otherwise precious technical solutions for users to remove some tasks according to predefined heuristic (based on soft or hard task), or by modifying the worst case execution times (WCETs), periods, and/or deadlines of tasks, that violate corresponding constraints by new ones, in order to meet deadlines and to minimize their response time. To handle all possible reconfiguration solutions, we propose an agent-based architecture that applies automatic reconfigurations in order to re-obtain the system's feasibility and to satisfy user requirements. Therefore, we developed the tool RT-Reconfiguration to support these contributions that we apply to a Blackberry Bold 9700 and to a Volvo system as running example systems and we apply the Real-Time Simulator Cheddar to check the whole system behavior and to evaluate the performance of the algorithm (detailed descriptions are available at the website: http://beru.univ-brest.fr/~singhoff/ cheddar). We present simulations of this architecture where we evaluate the agent that we implemented. Also, we present and discuss the results of experiments that compare the accuracy and the performance of our algorithm with others.

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