Time-Triggered Scheduling of Mixed-Criticality Systems

Distributed Computing and Internet Technology, 2017

Real-time safety-critical systems are getting more complex by integrating multiple applications with different criticality levels on a single platform. The increasing complexity in the design of mixedcriticality real-time systems has motivated researchers to move from uniprocessor to multiprocessor platforms. In this paper, we focus on the time-triggered scheduling of both independent and dependent mixedcriticality jobs on an identical multiprocessor platform. We show that our algorithm is more efficient than the Mixed criticality Priority Improvement (MCPI) algorithm, the only existing such algorithm for a multiprocessor platform.

IEEE Transactions on Computers, 2012

Many safety-critical embedded systems are subject to certification requirements; some systems may be required to meet multiple sets of certification requirements, from different certification authorities. Certification requirements in such "mixed-criticality” systems give rise to interesting scheduling problems, that cannot be satisfactorily addressed using techniques from conventional scheduling theory. In this paper, we study a formal model for representing such mixed-criticality workloads. We demonstrate first the intractability of determining whether a system specified in this model can be scheduled to meet all its certification requirements, even for systems subject to merely two sets of certification requirements. Then we quantify, via the metric of processor speedup factor, the effectiveness of two techniques, reservation-based scheduling and priority-based scheduling, that are widely used in scheduling such mixed-criticality systems, showing that the latter of the two is superior to the former. We also show that the speedup factors we obtain are tight for these two techniques.

2015 IEEE 17th International Conference on High Performance Computing and Communications, 2015 IEEE 7th International Symposium on Cyberspace Safety and Security, and 2015 IEEE 12th International Conference on Embedded Software and Systems, 2015

Modern safety-critical systems, such as avionics, tend to be mixed-critical, because integration of different tasks with different assurance requirements can effectively reduce their costs in terms of hardware, at the risk, however to increase the costs for certification, in particular in the context of proving their schedulability. To simplify the certification costs such systems use Time Triggered (TT) scheduling paradigm, and a generalization of the Time Triggered (TT) scheduling paradigm Single Time Mode (STTM). We present a state-of-the art STTM algorithm which works optimally on single core and shows good experimental results for multi-cores. In addition, because the algorithm can be applied on top of any memoryless scheduling policy, we show that applying it to list scheduling leads to support of task graph (precedence) dependencies and/or non-preemptive scheduling, for which our algorithm also shows good experimental results.

Modern safety-critical systems, such as avionics, tend to be mixed-critical, because integration of different tasks with different assurance requirements can effectively reduce their costs. Scheduling is one of the main challenges of such systems. In this work we show that a generalization of the Time Triggered (TT) scheduling paradigm, Single Time Mode (STTM) dominates other approaches like Fixed Priority or Fixed Priority per Mode (FPM). We also propose an algorithm to transform any FPM priority assignment to an equivalent set of STTM tables.

Real-time Systems, 2019

Modern real-time systems tend to be mixed-critical, in the sense that they integrate on the same computational platform applications at different levels of criticality (e.g., safety critical and mission critical). Scheduling of such systems is a popular topic in literature due to the complexity and importance of the problem. In this paper we propose two algorithms for job scheduling in mixed critical systems: mixed criticality earliest deadline first (MCEDF) and mixed critical priority improvement (MCPI). MCEDF is a single processor algorithm that theoretically dominates state-of-the-art fixed-priority algorithm own criticality based priority (OCBP), while having a better computational complexity. The dominance is achieved by profiting from a common extension of fixed-priority online policy to mixed criticality. MCPI is a multiprocessor algorithm that supports dependency constraints. Experiments show good schedulability results. Also we formally prove that both MCEDF and MCPI are optimal in a particular class of algorithms.

Siam Review, 2010

Many safety-critical embedded systems are subject to certification requirements; some systems may be required to meet multiple sets of certification requirements, from different certification authorities. Certification requirements in such "mixed-criticality" systems give rise to some interesting scheduling problems, that cannot be satisfactorily addressed using techniques from conventional scheduling theory. It had previously been shown that determining whether a system specified in this model can be scheduled to meet all its certification requirements is highly intractable. Prior work [4] had also introduced a simple, prioritybased scheduling algorithm called OCBP for mixed criticality systems, and had quantified, via the metric of processor speedup factor, the effectiveness of OCBP in scheduling dual-criticality systems -systems subject to two sets of certification requirements.

IEEE Transactions on Computers

Mixed-criticality models are an emerging paradigm for the design of real-time systems because of their significantly improved resource efficiency. However, formal mixed-criticality models have traditionally been characterized by two impractical assumptions: once any high-criticality task overruns, all low-criticality tasks are suspended and all other high-criticality tasks are assumed to exhibit highcriticality behaviors at the same time. In this paper, we propose a more realistic mixed-criticality model, called the flexible mixed-criticality (FMC) model, in which these two issues are addressed in a combined manner. In this new model, only the overrun task itself is assumed to exhibit high-criticality behavior, while other high-criticality tasks remain in the same mode as before. The guaranteed service levels of low-criticality tasks are gracefully degraded with the overruns of high-criticality tasks. We derive a utilization-based technique to analyze the schedulability of this new mixed-criticality model under EDF-VD scheduling. During run time, the proposed test condition serves an important criterion for dynamic service level tuning, by means of which the maximum available execution budget for low-criticality tasks can be directly determined with minimal overhead while guaranteeing mixed-criticality schedulability. Experiments demonstrate the effectiveness of the FMC scheme compared with state-of-the-art techniques.

IEEE Transactions on Computers

In this paper, we study the scheduling problem of the imprecise mixed-criticality model (IMC) under earliest deadline first with virtual deadline (EDF-VD) scheduling upon uniprocessor systems. Two schedulability tests are presented. The first test is a concise utilizationbased test which can be applied to the implicit deadline IMC task set. The suboptimality of the proposed utilization-based test is evaluated via a widely-used scheduling metric, speedup factors. The second test is a more effective test but with higher complexity which is based on the concept of demand bound function (DBF). The proposed DBF-based test is more generic and can apply to constrained deadline IMC task set. Moreover, in order to address the high time cost of the existing deadline tuning algorithm, we propose a novel algorithm which significantly improve the efficiency of the deadline tuning procedure. Experimental results show the effectiveness of our proposed schedulability tests, confirm the theoretical suboptimality results with respect to speedup factor, and demonstrate the efficiency of our proposed algorithm over the existing deadline tunning algorithm. In addition, issues related to the implementation of the IMC model under EDF-VD are discussed.

2017

This paper presents the practical implementation of a multi-core mixed-criticality scheduling algorithm. The goal of this work is to show the practical platform utilisation gain by allowing the concurrent execution of applications having different levels of criticality. We implemented the port of an existing industrial application provided by Thales Research & Technology on an embedded real-time operating system featuring task execution budget control, multi-core scheduling and multiple execution mode changes. We evaluated our solution by measuring the time that remains available for a low-criticality application running concurrently with the high-criticality use case mentioned above.

IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 2022

Many safety-critical real-time systems are considered certified when they meet failure probability requirements with respect to the maximum permitted incidences of failure per hour. In this paper, the mixed-criticality task model with multiple worst-case execution time (WCET) estimations is extended to incorporate such system-level certification restrictions. A new parameter is added to each task, characterizing the distribution of the WCET estimations-the likelihood of all jobs of a task finishing their executions within the less pessimistic WCET estimates. Efficient algorithms are derived for scheduling mixed-criticality systems represented using this model for both uniprocessor and multiprocessor platforms for independent tasks. Furthermore, a 0/1 covariance matrix is introduced to represent the failure-dependency between tasks. An efficient algorithm is proposed to schedule such failure-dependent tasks. Experimental analyses show our new model and algorithm outperform current state-of-the-art mixed-criticality scheduling algorithms.