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  • 51.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Fault Tolerant Scheduling of Mixed Criticality Real-Time Tasks under Error Bursts2015Ingår i: PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON INFORMATION AND COMMUNICATION TECHNOLOGIES, ICICT 2014, Kochi, India: Elsevier Procedia Computer Science , 2015, s. 1148-1155Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dependability is an important requirement in hard real-time applications due to the potentially catastrophic consequences of failures. In these systems, fault tolerance mechanisms like temporal redundancy are adopted to improve reliability. Most of these types of systems are increasingly moving towards integrating critical and non-critical functionalities on the same platform to, e.g., better utilize resources and further reduce cost, and are commonly deployed in environments where errors typically occur in the form of bursts e.g., due to Electro Magnetic Interference (EMI). Consequently, in mixed criticality real-time systems, the designer must guarantee that critical tasks are feasible even under the presence of the error burst, while ensuring the feasibility of the non-critical tasks that are not affected by the burst. We refer to this as {em Fault Tolerance feasibility} (FT-feasibility) of mixed-criticality real-time systems. In this paper, we build on the well established results on Earliest Deadline First (EDF) scheduling, to derive a sufficient test that determines the FT-feasibility of a set of mixed criticality real-time tasks under the assumption that the inter-arrival time between two consecutive error bursts is at least equal to the hyper-period of the taskset.

  • 52.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Preemption Control using CPU Frequency Scaling in Real-time Systems2011Ingår i: 18th INTERNATIONAL CONFERENCE ON CONTROL SYSTEMS AND COMPUTER SCIENCE, 2011, s. 88-95Konferensbidrag (Refereegranskat)
    Abstract [en]

    Controlling the preemption behavior in real-time systems can have beneficial impacts in multiple contexts as it can decrease the processor utilization, reduce the energy consumption or even enable the schedulability of the system. In this paper we study the preemption behavior of sporadic task systems scheduled using the Fixed Priority Scheduling (FPS) policy, and evaluate the feasibility of preemption control using CPU frequency scaling. We show that offline preemption control using CPU frequency scaling is difficult for sporadic task systems, and we propose an online heuristic algorithm, of linear complexity, to control the number of preemptions in a sporadic task system. Evaluation results show that online CPU frequency scaling is an attractive approach for preemption control in sporadic task systems.

  • 53.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Probabilistic Preemption Control using Frequency Scaling for Sporadic Real-time Tasks2012Ingår i: 7th IEEE International Symposium on IndustrialEmbedded Systems (SIES): Conference Proceedings, IEEE Computer Society, 2012, s. 158-165Konferensbidrag (Refereegranskat)
    Abstract [en]

    Preemption related costs are major sources of unpredictability in the task execution times in a real-time system. We examine the possibility of using CPU frequency scaling to control the preemption behavior of real-time sporadic tasks scheduled using a preemptive Fixed Priority Scheduling (FPS) policy. Our combined offline-online method provides probabilistic preemption control guarantees by making use of the release time probabilities of the sporadic tasks. The offline phase derives the probability related deviation from the minimum inter-arrival time of tasks. The online algorithm uses this information to calculate appropriate CPU frequencies that guarantees non-preemptive task executions while preserving the overall system schedulability. The online algorithm has a linear complexity and does not lead to significant implementation overheads. Our evaluations demonstrate the effectiveness of the method as well as the possibility of energy-preemption trade offs. Even though we have considered FPS, our method can easily be extended to dynamic priority scheduling schemes

  • 54.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Quantifying the Sub-Optimality of Non-Preemptive Real-time Scheduling2013Ingår i: Proceedings - Euromicro Conference on Real-Time Systems, 2013, 2013, s. 113-122Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A number of preemptive real-time scheduling algorithms, such as Earliest Deadline First (EDF), are known to be optimal on uni-processor systems under specified assumptions. However, no uni-processor optimal algorithm exists under the non-preemptive scheduling paradigm. Hence preemptive schemes strictly dominate non-preemptive schemes with respect to uni-processor feasibility. However, the 'goodness' of non-preemptive schemes, compared to uni-processor optimal preemptive scheduling schemes such as EDF, which can also be referred to as its sub-optimality, has not been fully investigated yet. In this paper, we apply resource augmentation, specifically processor speed-up, to quantify the sub-optimality of non-preemptive scheduling with respect to EDF, and apply the results to guarantee user specified upper-bounds on the preemption related scheduling costs. In particular, we derive an upper bound on the minimum processor speed-up required to guarantee the non-preemptive feasibility of tasks that are deemed feasible under the preemptive EDF, and we prove that, in the cases where, for all tasks in the task set, the largest execution requirement is not greater than the shortest deadline, this bound is equal to 4. We also show how the proposed approach enables a system designer to choose an optimal processor, in order to, e.g., guarantee specified upper bounds on the preemption related overheads.

  • 55.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    The Limited-preemptive Feasibility of Real-time Tasks on Uniprocessors2015Ingår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 51, nr 3, s. 247-273Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The preemptive scheduling paradigm is known to strictly dominate the non-preemptive scheduling paradigm with respect to feasibility. On the other hand, preemptively scheduling real-time tasks on uniprocessors, unlike non-preemptive scheduling, may lead to unschedulability due to, e.g., preemption related overheads. The limited-preemptive scheduling paradigm, which is a generalization of preemptive and non-preemptive paradigms, has, however, the potential to reduce the preemption related overheads while enabling high processor utilization. In this paper, we focus on the characterization of the effects of increasing the computational resources on the limited-preemptive feasibility of real-time tasks in order to quantify the sub-optimality of limited-preemptive scheduling. Specifically, we first derive the required processor speed-up bound that guarantees limited-preemptive feasibility of any uniprocessor feasible taskset. Secondly, we demonstrate the applicability of the results in the context of controlling preemption related overheads while minimizing the required processor speed-up. In particular, we identify the preemptive behavior that minimizes preemption-related overheads, as well as derive the optimal processor speed associated with it. Finally, we examine the consequences of having more processors on limited-preemptive feasibility and derive the bound on the number of processors that guarantees a specified limited-preemptive behavior for any uniprocessor feasible real-time taskset. This paper essentially bridges the preemptive and non-preemptive real-time scheduling paradigms by providing significant theoretical results building on the limitedpreemptive scheduling paradigm, as well as provides analytical inputs to developers in order to perform various trade-offs, e.g., code refactoring, to control the preemptive behavior of real-time tasks.

  • 56.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Towards Preemption Control Using CPU Frequency Scaling in Sporadic Task Systems2011Ingår i: SIES 2011 - 6th IEEE International Symposium on Industrial Embedded Systems, Conference Proceedings, Vasteras, 2011, s. 35-38Konferensbidrag (Refereegranskat)
    Abstract [en]

    Preemptions in real-time systems scheduling typically lead to variations in task execution times, increase the temporal overhead required for various RTOS related operations and may even cause unschedulability.We examine the preemption behavior of sporadic tasks scheduled under the Fixed Priority Scheduling (FPS) policy, and evaluate the possibility of using CPU frequency scaling for preemption control. We propose an online heuristic-based algorithm, of linear complexity, to control the number of preemptions in a sporadic task system using CPU frequency scaling. Evaluation results show that CPU frequency scaling is an attractive option to control the preemption behavior of real-time sporadic task systems.

  • 57.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Using Processor Speed-up to Control Preemption Related Costs2013Rapport (Övrigt vetenskapligt)
  • 58.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Aysan, Huseyin
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Resource Augmentation for Fault-Tolerance Feasibility of Real-time Tasks under Error Bursts2012Ingår i: Proceedings of the 20th International Conference on Real-Time and Network Systems (RTNS 12), Association for Computing Machinery (ACM), 2012, s. 41-50Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dependability is a vital system requirement, particularly in safety critical and mission critical real-time systems, due to the potentially catastrophic consequences of failures. In most critical applications different fault tolerance mechanisms using redundancy are employed to prevent possible failures. In the case of real-time systems the system designer must ensure that the task set is feasible even under faults, which we refer to as 'fault tolerance feasibility'. Due to cost considerations, often temporal redundancy has been prevalently used to meet this objective.

    In this paper we focus on guaranteeing fault-tolerance feasibility under error bursts on uni-processor systems by the usage of resource augmentation, specifically through processor speed-up. Firstly, we derive a processor demand bound based sufficient condition for a set of real-time tasks to be fault tolerance feasible under an assumption that no more than one error burst occurs during the hyper-period of the task set. Subsequently, we derive the necessary resource augmentation bounds (i.e., the processor speed-up), that guarantees the fault tolerance feasibility, if the sufficient test fails. Finally, we prove that, if the error burst length is no more than half the shortest relative deadline of the task set, the minimum processor speed-up required to guarantee fault tolerance feasibility is upper-bounded by 6.

  • 59.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Pillai, Anju
    Amrita School of Engineering, Amrita Vishwa Vidyapeetham, India .
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Preemption Control Using Frequency Scaling in Fixed Priority Scheduling2010Ingår i: Proceedings - IEEE/IFIP International Conference on Embedded and Ubiquitous Computing, EUC 2010, 2010, s. 281-288Konferensbidrag (Refereegranskat)
    Abstract [en]

    Controlling the number of preemptions in realtime systems is highly desirable in order to achieve an efficient system design in multiple contexts. For example, the delays due to context switches account for high preemption overheads which detrimentally impact the system schedulability. Preemption control can also be potentially used for the efficient control of critical section behaviors in multi-threaded applications. At the same time, modern processor architectures provide for the ability to selectively choose operating frequencies, primarily targeting energy efficiency as well as system performance. In this paper, we propose the use of CPUFrequency Scaling for controlling the preemptive behavior of real-time tasks. We present a framework for selectively eliminating preemptions, that does not require modifications to the task attributes or to the underlying scheduler. We evaluate the proposed approach by four different heuristics through extensive simulation studies. 

  • 60.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Pillai, Anju S
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Reducing the Number of Preemptions in Real-Time Systems Scheduling by CPU Frequency Scaling2010Ingår i: 18th International Conference on Real-Time and Network Systems, Toulouse, France, 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Controlling the number of preemptions in real-time systems is highly desirable in order to achieve an efficient system design in multiple contexts. For example, the delays due to context switches account for high preemption overheads which detrimentally impact the system schedulability. Preemption avoidance can also be potentially used for the efficient control of critical section behaviors in multi-threaded applications. At the same time, modern processor architectures provide for the ability to selectively choose operating frequencies, primarily targeting energy efficiency as well as system performance. In this paper, we propose the use of CPU Frequency Scaling for controlling the preemptive behavior of real-time tasks. We present a framework for selectively eliminating preemptions, that does not require modifications to the task attributes or to the underlying scheduler. We evaluate the proposed approach by four different heuristics through extensive simulation studies.

  • 61.
    Thekkilakattil, Abhilash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Zhu, K.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Nie, Y.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Punnekkat, S.
    Birla Institute of Technology and Science, Goa, India.
    An empirical investigation of eager and lazy preemption approaches in global limited preemptive scheduling2016Ingår i: Lecture Notes in Computer Science, Springer, 2016, s. 163-178Konferensbidrag (Refereegranskat)
    Abstract [en]

    Global limited preemptive real-time scheduling in multiprocessor systems using Fixed Preemption Points (FPP) brings in an additional challenge with respect to the choice of the task to be preempted in order to maximize schedulability. Two principal choices with respect to the preemption approach exist (1) the scheduler waits for the lowest priority job to become preemptible, (2) the scheduler preempts the first job, among the lower priority ones, that becomes preemptible. We refer to the former as the Lazy Preemption Approach (LPA) and the latter as the Eager Preemption Approach (EPA). Each of these choice has a different effect on the actual number of preemptions in the schedule, that in turn determine the runtime overheads. In this paper, we perform an empirical comparison of the run-time preemptive behavior of Global Preemptive Scheduling and Global Limited Preemptive Scheduling with EPA and LPA, under both Earliest Deadline First (EDF) and Fixed Priority Scheduling (FPS) paradigms. Our experiments reveal interesting observations some of which are counterintuitive. We then analyse the counter-intuitive observations and identify the associated reasons. The observations presented facilitate the choice of appropriate strategies when using limited preemptive schedulers on multiprocessor systems.

  • 62.
    Thekkilakattil, Abilsash
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Dobrin, Radu
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Punnekkat, Sasikumar
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Mixed criticality scheduling in fault-tolerant distributed real-time systems2014Ingår i: International Conference on Embedded Systems, ICES 2014, 2014, s. 92-97Konferensbidrag (Refereegranskat)
    Abstract [en]

    Modern safety critical real-time systems are composed of tasks of mixed criticalities and the problem of scheduling them in a fault tolerant manner, on a distributed platform, is challenging. Fault tolerance is typically achieved by using redundancy techniques, most commonly in the form of temporal redundancy which involves executing an alternate task before the original deadline of the failed task. Additionally, studies like Zonal Hazard Analysis (ZHA) and Fault Hazard Analysis (FHA) may impose extra constraints on the re-executions, e.g., spatial separation of alternates, to improve reliability. In this paper, we present a method for scheduling mixed criticality real-time tasks on a distributed platform in a fault tolerant manner while taking into account the recommendations given by the reliability studies like ZHA and FHA. First, we use mathematical optimization to allocate tasks on the processors, and then derive fault tolerant and fault aware feasibility windows for the critical and non-critical tasks respectively. Finally, we derive scheduler specific task attributes like priorities for the fixed priority scheduler. Our method provides hard real-time fault tolerance guarantees for critical tasks while maximizing resource utilization for non-critical tasks.

12 51 - 62 av 62
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