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Real-Time Systems (ECRTS), 2013 25th Euromicro Conference on

Date 9-12 July 2013

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Displaying Results 1 - 25 of 41
  • [Front cover]

    Page(s): C4
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  • [Title page i]

    Page(s): i
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  • [Title page iii]

    Page(s): iii
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  • [Copyright notice]

    Page(s): iv
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  • Table of contents

    Page(s): v - viii
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  • Message from the Program Chair

    Page(s): ix
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  • Organizing Committee

    Page(s): x
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  • Program Committee

    Page(s): xi
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  • Outstanding Papers Awards

    Page(s): xii
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  • Workshops

    Page(s): xiii
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  • Reviewers

    Page(s): xiv
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  • Keynote abstracts

    Page(s): xv - xvi
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    These keynote speeches discuss the following: unmanned European spacecraft communications; and domain control unit virtualisation. View full abstract»

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  • Outstanding Paper Award: Analysis of Global EDF for Parallel Tasks

    Page(s): 3 - 13
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1077 KB) |  | HTML iconHTML  

    As multicore processors become ever more prevalent, it is important for real-time programs to take advantage of intra-task parallelism in order to support computation-intensive applications with tight deadlines. We prove that a Global Earliest Deadline First (GEDF) scheduling policy provides a capacity augmentation bound of 4-2/m and a resource augmentation bound of 2-1/m for parallel tasks in the general directed a cyclic graph model. For the proposed capacity augmentation bound of 4-2/m for implicit deadline tasks under GEDF, we prove that if a task set has a total utilization of at most m/(4-2/m) and each task's critical path length is no more than 1/(4-2/m) of its deadline, it can be scheduled on a machine with m processors under GEDF. Our capacity augmentation bound therefore can be used as a straightforward schedulability test. For the standard resource augmentation bound of 2-1/m for arbitrary deadline tasks under GEDF, we prove that if an ideal optimal scheduler can schedule a task set on m unit-speed processors, then GEDF can schedule the same task set on m processors of speed 2-1/m. However, this bound does not lead to a schedulabilty test since the ideal optimal scheduler is only hypothetical and is not known. Simulations confirm that the GEDF is not only safe under the capacity augmentation bound for various randomly generated task sets, but also performs surprisingly well and usually outperforms an existing scheduling technique that involves task decomposition. View full abstract»

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  • Reducing Tardiness under Global Scheduling by Splitting Jobs

    Page(s): 14 - 24
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (461 KB) |  | HTML iconHTML  

    Under current analysis, soft real-time tardiness bounds applicable to global earliest-deadline-first scheduling and related policies depend on per-task worst-case execution times. By splitting job budgets to create sub jobs with shorter periods and worst-case execution times, such bounds can be reduced to near zero for implicit-deadline sporadic task systems. However, doing so could potentially cause more preemptions and create problems for synchronization protocols. This paper analyzes this tradeoff between theory and practice by presenting an overhead-aware schedulability study pertaining to job splitting. In this study, real overhead data from a scheduler implementation in LITMUSRT was factored into schedulability analysis. This study shows that despite practical issues affecting job splitting, it can still yield substantial reductions in tardiness bounds for soft real-time systems. View full abstract»

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  • Global EDF Schedulability Analysis for Synchronous Parallel Tasks on Multicore Platforms

    Page(s): 25 - 34
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB) |  | HTML iconHTML  

    The trend towards multi-core/many-core architectures is well underway. It is therefore becoming very important to develop software in ways that take advantage of such parallel architectures. This particularly entails a shift in programming paradigms towards fine-grained, thread-parallel computing. Many parallel programming models have been introduced targeting such intra-task thread-level parallelism. However, most successful results on traditional multi-core real-time scheduling are focused on sequential programming models. For example, thread-level parallelism is not properly captured into the concept of interference, which is key to many schedulability analysis techniques. Thereby, most interference-based analysis techniques are not directly applicable to parallel programming models. Motivated by this, we extend the notion of interference to capture thread-level parallelism more accurately. We then leverage the proposed notion of parallelism-aware interference to derive efficient EDF schedulability tests that are directly applicable to synchronous parallel task models on multi-core platforms. Our evaluation results indicate that the proposed analysis significantly advances the state-of-the-art in EDF schedulability analysis for synchronous parallel tasks. View full abstract»

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  • Achieving Thermal-Resiliency for Multicore Hard-Real-Time Systems

    Page(s): 37 - 46
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1070 KB) |  | HTML iconHTML  

    Multicore processor based system designs are increasingly utilized as the processing platform for complex hard-real-time and embedded applications. These real-time systems need to operate under various physical and design constraints. Much research has focused on thermal-aware real-time systems designs. However, no results exist to investigate the resource allocation and the system degradation under external thermal constraints in a predictable manner. This paper proposes a control-theoretic framework to ensure hard-real-time deadlines on a multiprocessor platform in a dynamic thermal environment. We use real-time performance modes to permit the system to adapt to changing conditions. Also, we show how the system designer can use our framework to allocate asymmetric processing resources upon a multicore CPU and still maintain thermal constraints. We develop analysis for determining what modes the system can support for a given external thermal condition. Our system design extends the derivation of thermal-resiliency (originally proposed for uniprocessor systems) to multicore systems and determines the limitations of external thermal stress that any hard-real-time performance mode can withstand. Simulations and physical test bed results show that our algorithm predicts how a system will gracefully and predictably degrade under external thermal stress. View full abstract»

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  • The Optimality of PFPasap Algorithm for Fixed-Priority Energy-Harvesting Real-Time Systems

    Page(s): 47 - 56
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB) |  | HTML iconHTML  

    The paper addresses the real-time fixed-priority scheduling problem for battery-powered embedded systems whose energy storage unit is replenished by an environmental energy source. In this context, a task may meet its deadline only if its cost of energy can be satisfied early enough. Hence, a scheduling policy for such a system should account for properties of the source of energy, capacity of the energy storage unit and tasks cost of energy. Classical fixed-priority schedulers are no more suitable for this model. Based on these motivations, we propose PFPASAP an optimal scheduling algorithm that handles both energy and timing constraints. Furthermore, we state the worst case scenario for non concrete task sets a non concrete task set is a set of real-time tasks whose offsets are known only at run-time scheduled with this algorithm and build a necessary and sufficient feasibility condition for non concrete task sets. Moreover, a minimal bound of the storage unit capacity that keeps a task set schedulable with PFPASAP is also proposed. Finally, we validate the proposed theory with large scale simulations and compare our algorithm with other existing ones. View full abstract»

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  • A Game-Theoretic Resource Manager for RT Applications

    Page(s): 57 - 66
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (557 KB) |  | HTML iconHTML  

    The management of resources among competing QoS-aware applications is often solved by a resource manager (RM) that assigns both the resources and the application service levels. However, this approach requires all applications to inform the RM of the available service levels. Then, the RM has to maximize the "overall quality" by comparing service levels of different applications which are not necessarily comparable. In this paper we describe a Linux implementation of a game-theoretic framework that decouples the two distinct problems of resource assignment and quality setting, solving them in the domain where they naturally belong to. By this approach the RM has linear time complexity in the number of the applications. Our RM is built over the SCHED_DEADLINE Linux scheduling class. View full abstract»

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  • Outstanding Paper Award: Schedulability Analysis of the Linux Push and Pull Scheduler with Arbitrary Processor Affinities

    Page(s): 69 - 79
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (711 KB) |  | HTML iconHTML  

    Contemporary multiprocessor real-time operating systems, such as VxWorks, LynxOS, QNX, and real-time variants of Linux, allow a process to have an arbitrary processor affinity, that is, a process may be pinned to an arbitrary subset of the processors in the system. Placing such a hard constraint on process migrations can help to improve cache performance of specific multi-threaded applications, achieve isolation among components, and aid in load-balancing. However, to date, the lack of schedulability analysis for such systems prevents the use of arbitrary processor affinities in predictable hard real-time applications. In this paper, it is shown that job-level fixed-priority scheduling with arbitrary processor affinities is strictly more general than global, clustered, and partitioned job-level fixed-priority scheduling. The Linux push and pull scheduler is studied as a reference implementation and techniques for the schedulability analysis of hard real-time tasks with arbitrary processor affinity masks are presented. The proposed tests work by reducing the scheduling problem to ``global-like'' sub-problems to which existing global schedulability tests can be applied. Schedulability experiments show the proposed techniques to be effective. View full abstract»

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  • A Coordinated Approach for Practical OS-Level Cache Management in Multi-core Real-Time Systems

    Page(s): 80 - 89
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (457 KB) |  | HTML iconHTML  

    Many modern multi-core processors sport a large shared cache with the primary goal of enhancing the statistic performance of computing workloads. However, due to resulting cache interference among tasks, the uncontrolled use of such a shared cache can significantly hamper the predictability and analyzability of multi-core real-time systems. Software cache partitioning has been considered as an attractive approach to address this issue because it does not require any hardware support beyond that available on many modern processors. However, the state-of-the-art software cache partitioning techniques face two challenges: (1) the memory co-partitioning problem, which results in page swapping or waste of memory, and (2) the availability of a limited number of cache partitions, which causes degraded performance. These are major impediments to the practical adoption of software cache partitioning. In this paper, we propose a practical OS-level cache management scheme for multi-core real-time systems. Our scheme provides predictable cache performance, addresses the aforementioned problems of existing software cache partitioning, and efficiently allocates cache partitions to schedule a given task set. We have implemented and evaluated our scheme in Linux/RK running on the Intel Core i7 quad-core processor. Experimental results indicate that, compared to the traditional approaches, our scheme is up to 39% more memory space efficient and consumes up to 25% less cache partitions while maintaining cache predictability. Our scheme also yields a significant utilization benefit that increases with the number of tasks. View full abstract»

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  • Mixed Critical Earliest Deadline First

    Page(s): 93 - 102
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB) |  | HTML iconHTML  

    Using the advances of the modern microelectronics technology, the safety-critical systems, such as avionics, can reduce their costs by integrating multiple tasks on one device. This makes such systems essentially mixed-critical, as this brings together different tasks whose safety assurance requirements may differ significantly. In the context of mixed-critical scheduling theory, we studied the dual criticality problem of scheduling a finite set of hard real-time jobs. In this work we propose an algorithm which is proved to dominate OCBP, a state-of-the art algorithm for this problem that is optimal over fixed job priority algorithms. We show through empirical studies that our algorithm can reduce the set of non-schedulable instances by a factor of two or, under certain assumptions, by a factor of four, when compared to OCBP. View full abstract»

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  • Computation Offloading for Frame-Based Real-Time Tasks with Resource Reservation Servers

    Page(s): 103 - 112
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (399 KB) |  | HTML iconHTML  

    Computation offloading concept has been recently adopted to improve the performance of embedded systems by moving some computation-intensive tasks (partially or wholly) to a powerful remote server. In this paper, we consider a computation offloading problem for frame-based real-time tasks, in which all the tasks have the same arrival time and the same relative deadline/period, by adopting the total bandwidth server (TBS) as resource reservations in the server side (remote execution unit). We prove that the problem is N P-complete and propose two algorithms in this paper. The first algorithm is a greedy algorithm with low complexity and provides a quick heuristic approach to decide which tasks to be offloaded and how the tasks are scheduled. The maximum finishing time of the solution derived from the greedy algorithm is at most twice of the finishing time (make span, maximal on the client and on the server) of any schedule. The second algorithm is a dynamic programming approach, which builds a three-dimensional table and requires pseudo-polynomial time complexity, to make an optimal decision for computation offloading. The algorithms are evaluated with a case study of a surveillance system and synthesized benchmarks. View full abstract»

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  • Quantifying the Sub-optimality of Non-preemptive Real-Time Scheduling

    Page(s): 113 - 122
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (665 KB) |  | HTML iconHTML  

    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. View full abstract»

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  • Mixed Criticality on Controller Area Network

    Page(s): 125 - 134
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB) |  | HTML iconHTML  

    An increasingly important trend in the design of real-time and embedded systems is the integration of components with different levels of criticality onto a common hardware platform. Where the platform incorporates a communication media it is necessary for that media to be able to safely and efficiently transfer messages of different criticality levels. In this paper we consider the Controller Area Network (CAN), and define mixed criticality protocols that could form the basis of a Trusted Network Component for CAN. Sufficient response-time analysis is derived for these protocols and an optimal priority assignment scheme is provided. Evaluations illustrate the benefits of the schemes. View full abstract»

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  • Probabilistic Timing Analysis for the Dynamic Segment of FlexRay

    Page(s): 135 - 144
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (377 KB) |  | HTML iconHTML  

    We propose an analytical framework for probabilistic timing analysis of the event-triggered Dynamic segment of the Flex Ray communication protocol. Specifically, our framework computes the Deadline Miss Ratios of each message. The core problem is formulated as a Mixed Integer Linear Program (MILP). Given the intractability of the problem, we also propose several techniques that help to mitigate the running times of our tool. This includes the re-engineering of the problem to run it on GPUs as well as re-formulating the MILP itself. View full abstract»

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