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The preemptive uniprocessor scheduling of mixed-criticality implicit-deadline sporadic task systems
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Bounding and Shaping the Demand of Mixed-Criticality Sporadic Tasks
"... Abstract—We derive demand-bound functions for mixedcriticality sporadic tasks, and use these to determine EDFschedulability. Tasks have different demand-bound functions for each criticality mode. We show how to shift execution demand from high- to low-criticality mode by tuning the relative deadline ..."
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Cited by 19 (4 self)
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Abstract—We derive demand-bound functions for mixedcriticality sporadic tasks, and use these to determine EDFschedulability. Tasks have different demand-bound functions for each criticality mode. We show how to shift execution demand from high- to low-criticality mode by tuning the relative deadlines. This allows us to shape the demand characteristics of each task. We propose an efficient algorithm for tuning all relative deadlines of a task set in order to shape the total demand to the available supply of the computing platform. Experiments indicate that this approach is significantly more powerful than previous approaches to mixed-criticality scheduling. This new approach has the added benefit of supporting hierarchical scheduling frameworks. I.
Relaxing mixed-criticality scheduling strictness for task sets scheduled with FP
- In Proc. of the Euromicro Conference on Real-Time Systems
, 2012
"... Abstract—Current trends in the embedded systems field tend to collocate multiple functionalities upon a single computing plat-form, the aim being to reduce both the size and cost of embedded systems. Nevertheless, it is unlikely that all functionalities share the same level of criticality, and certi ..."
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Cited by 13 (0 self)
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Abstract—Current trends in the embedded systems field tend to collocate multiple functionalities upon a single computing plat-form, the aim being to reduce both the size and cost of embedded systems. Nevertheless, it is unlikely that all functionalities share the same level of criticality, and certification of the system has to be achieved using varying degrees of rigorousness. Typically, a task τi is guaranteed to meet its temporal constraints up to a criticality level that is equal to its own criticality. When those conditions are no longer met, i.e. when another higher priority task τj has its execution time that exceeds its Worst Case Execution Time (WCET) w.r.t. the criticality level of τi, a common approach is to suspend τi. However, in some cases, it may not be necessary to suspend tasks with a lower criticality immediately as they could still be executed without compromising the deadlines of high criticality tasks. As a step towards this aim, we propose a method, denoted Latest Completion Time (LCT), that allows lower criticality tasks to proceed with their execution as long as they do not prevent higher criticality tasks from meeting their deadlines. Furthermore, we show that tasks suspension can only be temporary, and prove that a particular definition of idle times can be used to reset the system’s criticality level. Finally, we study the performances of our LCT mechanism w.r.t. the classical mechanism that suspends a task as soon as the system criticality level becomes higher than its own criticality.
Bounding and shaping the demand of generalized mixed-criticality sporadic task systems
- Real-Time Systems
, 2014
"... Abstract We generalize the commonly used mixed-criticality sporadic task model to let all task parameters (execution-time, deadline and period) change between criti-cality modes. In addition, new tasks may be added in higher criticality modes and the modes may be arranged using any directed acyclic ..."
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Cited by 9 (4 self)
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Abstract We generalize the commonly used mixed-criticality sporadic task model to let all task parameters (execution-time, deadline and period) change between criti-cality modes. In addition, new tasks may be added in higher criticality modes and the modes may be arranged using any directed acyclic graph, where the nodes represent the different criticality modes and the edges the possible mode switches. We for-mulate demand bound functions for mixed-criticality sporadic tasks and use these to determine EDF-schedulability. Tasks have different demand bound functions for each criticality mode. We show how to shift execution demand between different criticality modes by tuning the relative deadlines. This allows us to shape the demand character-istics of each task. We propose efficient algorithms for tuning all relative deadlines of a task set in order to shape the total demand to the available supply of the computing platform. Experiments indicate that this approach is successful in practice. This new approach has the added benefit of supporting hierarchical scheduling frameworks.
Towards a more practical model for mixed criticality systems
- In WMC
, 2013
"... Abstract-Mixed Criticality Systems (MCSs) have been the focus of considerable study over the last six years. This work has lead to the definition of a standard model that allows processors to be shared efficiently between tasks of different criticality levels. Key aspects of this model are that a s ..."
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Cited by 6 (2 self)
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Abstract-Mixed Criticality Systems (MCSs) have been the focus of considerable study over the last six years. This work has lead to the definition of a standard model that allows processors to be shared efficiently between tasks of different criticality levels. Key aspects of this model are that a system is deemed to execute in one of a small number of criticality modes; initially the system is in the lowest criticality mode, but if any task executes for more than its predefined budget for this criticality level then a mode change is made to a higher criticality mode and all tasks of the lowest criticality level are abandoned (aborted). The initial criticality level is never revisited. This model has been useful in defining key properties of MCSs, but it does not form a useful basis for an actual implementation of a MCS. In this paper we consider the tradeoffs stemming from a consideration of what systems engineers require at run-time and the actual properties of the model that scheduling analysis guarantees. Alternative models are defined that allow low criticality tasks to continue to execute after a criticality mode change. The paper also addresses robust priority assignment.
Mixed Critical Earliest Deadline First
, 2012
"... 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 error probability require ..."
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Cited by 3 (1 self)
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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 error probability requirements may differ by an order of magnitude 10 6. In the context of mixed-critical scheduling theory, we studied the problem of scheduling a finite set of jobs. In this work we propose an algorithm which is proved to dominate OCBP, one of the best scheduling algorithms for this problem. We show through empirical studies that our algorithm can reduce the set of non-schedulable instances by a factor of 2.5 or, under certain assumptions, by a factor of 4.5, when compared to OCBP.
Adaptive Mixed Criticality Scheduling with Deferred Preemption
"... Abstract—Adaptive Mixed Criticality (AMC) scheduling has previously been shown to be the most effective fixed priority approach for scheduling mixed criticality systems, while the idea of final non-preemptive regions has been shown to improve the schedulability of systems with a single criticality l ..."
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Cited by 2 (2 self)
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Abstract—Adaptive Mixed Criticality (AMC) scheduling has previously been shown to be the most effective fixed priority approach for scheduling mixed criticality systems, while the idea of final non-preemptive regions has been shown to improve the schedulability of systems with a single criticality level. In this paper, we combine AMC with the concept of non-preemptive regions by making the final part of each task’s execution at each criticality level non-preemptive. We derive schedulability analysis for this approach, and provide an effective algorithm for choosing each task’s priority and the durations of its non-preemptive regions. Evaluations illustrate the benefits of this approach in terms of increased schedulability. I.
A Bailout Protocol for Mixed Criticality Systems
"... Abstract—To move mixed criticality research into industrial practice requires models whose run-time behaviour is acceptable to systems engineers. Certain aspects of current models, such as abandoning lower criticality tasks when certain situations arise, do not give the robustness required in applic ..."
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Abstract—To move mixed criticality research into industrial practice requires models whose run-time behaviour is acceptable to systems engineers. Certain aspects of current models, such as abandoning lower criticality tasks when certain situations arise, do not give the robustness required in application domains such as the automotive and aerospace industries. In this paper a new bailout protocol is developed that still guarantees high criticality tasks but minimises the negative impact on lower criticality tasks via a timely return to normal operation. We show how the bailout protocol can be integrated with existing techniques, utilising offline slack to further improve performance. Static analysis is provided for the strong schedulability guarantees, while scenario-based evaluation via simulation is used to explore the effectiveness of the protocol. I.
Scheduling Algorithms for Elastic Mixed-Criticality Tasks in Multicore Systems
, 2013
"... Abstract—The Elastic Mixed-Criticality (E-MC) task model and an Early-Release EDF (ER-EDF) scheduling algorithm have been studied to address the service interruption problem for lowcriticality tasks in uniprocessor systems, where the minimum service requirements of low-criticality tasks are guarante ..."
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Abstract—The Elastic Mixed-Criticality (E-MC) task model and an Early-Release EDF (ER-EDF) scheduling algorithm have been studied to address the service interruption problem for lowcriticality tasks in uniprocessor systems, where the minimum service requirements of low-criticality tasks are guaranteed by their maximum periods. In this paper, focusing on multicore systems, we first investigate and empirically evaluate the schedulability of E-MC tasks under partitioned-EDF (P-EDF) by considering various task-to-core mapping heuristics. Then, to improve the service levels of low-criticality tasks by exploiting slack at runtime, with and without task migrations being considered, we study both global and local early-release schemes. Moreover, considering varied migration overheads between different cores, we propose the multicore-aware and migration constrained global-ER schemes. The simulation results show that, compared to the state-of-the-art Global EDF-VD scheduler, P-EDF with various partitioning heuristics can lead to many more schedulable E-MC task sets. Moreover, our proposed global and local ER schemes can significantly improve the execution frequencies (and thus service levels) of low-criticality tasks, while Global EDF-VD may severely affect them by discarding most of their task instances at runtime (especially for systems with more cores). Furthermore, by allowing task migrations, global-ER schemes can dramatically improve low-criticality tasks ’ service levels for partitionings that do not balance high- and low-criticality tasks among the cores. I.
Design Optimization of Security-Sensitive Mixed-Criticality Real-Time Embedded Systems
"... Abstract—In this paper we are interested in securitysensitive mixed-criticality real-time systems. Existing researches on mixed-criticality systems usually are safety-oriented, which seriously ignore the security requirements. We firstly establish the system model to capture security-critical applic ..."
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Abstract—In this paper we are interested in securitysensitive mixed-criticality real-time systems. Existing researches on mixed-criticality systems usually are safety-oriented, which seriously ignore the security requirements. We firstly establish the system model to capture security-critical applications in mixed-criticality systems. Higher security-criticality protection always results in significant time and energy overhead in mixedcriticality systems. Thus, this paper proposes a system-level design framework for energy optimization of security-sensitive mixed-criticality system. Since the time complexity of finding optimal solutions grows exponentially as problem size grows, a GA based efficient heuristic algorithm is devised to address the system-level optimization problem. Extensive experiments demonstrate the efficiency of the proposed technique, which can obtain balanced minimal energy consumption while satisfying strict security and timing constraints. I.
