Dynascore

29th International Conference on Real-Time Networks and Systems, 2021

In conventional real-time systems analysis, each system parameter is specified by a single estimate, which must pessimistically cover the worst case. Mixed-criticality (MC) design has been proposed to mitigate such pessimism by providing a single system parameter with multiple estimates, which often lead to low-critical and highcritical modes. The majority of the works on MC scheduling is based on the approach that low-critical workloads are (fully or partially) sacrificed at the transition instant from low-to high-critical mode. Recently, another approach called precise MC scheduling has been investigated, where no low-critical workload is sacrificed at the mode switch, but instead a processor speed boosting is committed. In this paper, we extend the work on uniprocessor precise MC scheduling to multiprocessor platforms. To tackle this new scheduling problem, we propose two novel algorithms based on the virtualdeadline and fluid-scheduling approaches. For each approach, we present a sufficient schedulability test and prove its correctness. We also evaluate their effectiveness theoretically with speedup bounds and approximation factors as well as experimentally via randomly generated task sets. CCS CONCEPTS • Computer systems organization → Real-time systems.

2012

In mixed-criticality systems, functionalities of different degrees of importance (or criticalities) are implemented upon a common platform. Such mixed-criticality implementations are becoming increasingly common in embedded systems – consider, for example, the Integrated Modular Avionics (IMA) software architecture used in aviation [5] and the AUTOSAR initiative (AUTomotive Open System ARchitecture – www.autosar.org) for automotive systems. As a consequence the real-time systems research community has recently been devoting much attention to better understanding the challenges that arise in implementing such mixed-criticality systems; this includes research on various aspects of mixed-criticality scheduling. Most of this prior work draws inspiration from the seminal work of Vestal [6], and has taken the approach of validating the correctness of highly critical functionalities under more pessimistic assumptions than the assumptions used in validating the correctness of less critical ...

OpenBU, 2018

Mixed-criticality model of computation is being increasingly adopted in timing-sensitive systems. The model not only ensures that the most critical tasks in a system never fails, but also aims for better systems resource utilization in normal condition. In this report, we describe the widely used mixed-criticality task model and fixed-priority scheduling algorithms for the model in uniprocessors. Because of the necessity by the mixed-criticality task model and scheduling policies, isolation, both temporal and spatial, among tasks is one of the main requirements from the system design point of view. Different virtualization techniques have been used to design system software architecture with the goal of isolation. We discuss such a few system software architectures which are being and can be used for mixed-criticality model of computation

Cyber-Physical Systems: A Reference, 2018

Due to cost, size, weight, heat generation, and power consumption considerations, there is an increasingly important trend in cyber-physical systems (CPS) design toward mixed-criticality (MC) implementations, where applications at different importance levels are implemented upon a shared platform. Traditional design practice has been to provision computing resources to more critical applications more conservatively than to less-critical ones. In MC-based design, such over-provisioned resources may be shared by the less-critical functionalities under normal circumstances; this often allows for much more efficient resource

HAL (Le Centre pour la Communication Scientifique Directe), 2018

The safety critical industry is considering a shift from single-core COTS to multi-core COTS processors for safety and time critical computers in order to maximize performance while reducing costs. In a domain where time predictability is a major concern due to the regulation standards, multi-core processors are introducing new sources of time variations due to the electronic competition when the software is accessing shared hardware resources, and characterized by timing interference. The solutions proposed in the literature to deal with timing interference are all proposing a trade-off between performance efficiency, time predictability and intrusiveness in the software. Especially, none of them is able to fully exploit the multicore efficiency while allowing untouched, already-certified legacy software to run. In this paper, we introduce and evaluate BB-RTE, a Budget-Based RunTime Engine for Mixed & Safety Critical Systems, that especially focuses on mixed critical systems. BB-RTE aims at guaranteeing the deadline of high-critical tasks 1) by computing for each shared hardware resource a budget in terms of extra accesses that the critical tasks can support before their runtime is significantly impacted; 2) by temporarily suspending low-critical tasks at runtime once this budget has been consumed.

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.

2014

When integrating mixed critical systems on a multi/manycore, one challenge is to ensure predictability for high criticality tasks and an increased utilization for low criticality tasks. In this paper, we address this problem when several high criticality tasks with different deadlines, periods and offsets are concurrently executed on the system. We propose a distributed run-time WCET controller that works as follows: (1) locally, each critical task regularly checks if the interferences due to the low criticality tasks can be tolerated, otherwise it decides their suspension; (2) globally, a master suspends and restarts the low criticality tasks based on the received requests from the critical tasks. Our approach has been implemented as a software controller on a real multi-core COTS system with significant gains 1. 1 The research leading to these results has received funding from the TORRENTS cluster supported by the RTRA STAE and the European FP7-ICT project DREAMS under reference n • 610640.

2012

Abstract Shared resource access interference, particularly memory and system bus, is a big challenge in designing predictable real-time systems because its worst case behavior can significantly differ. In this paper, we propose a software based memory throttling mechanism to explicitly control the memory interference. We developed analytic solutions to compute proper throttling parameters that satisfy schedulability of critical tasks while minimize performance impact caused by throttling.

2018 IEEE Real-Time Systems Symposium (RTSS), 2018

The traditional mixed-criticality (MC) model does not allow less critical tasks to execute during an event of the error and exception. Recently, the imprecise MC (IMC) model has been proposed where, even for exceptional events, less critical tasks also receive some amount of (degraded) service, e.g., a task overruns its execution demand. In this work, we present our ongoing effort to extend the IMC model to the precise scheduling of tasks and integrate with the dynamic voltage and frequency scaling (DVFS) scheme to enable energy minimization. Precise scheduling of MC systems is highly challenging because of its requirement to simultaneously guarantee the timing correctness of all tasks under both pessimistic and less pessimistic assumptions. We propose an utilization-based schedulability test and sufficient schedulability conditions for such systems under earliest deadline first with virtual deadline (EDF-VD) scheduling policy. For this unified model, we present a quantitative study...

Dependable Software Engineering. Theories, Tools, and Applications, 2018

Due to size, weight, and power considerations, there is an emerging trend in real-time embedded systems design towards implementing functionalities of different levels of importance upon a shared platform, or implementing Mixed-Criticality (MC) systems. Much existing work on MC scheduling focuses on the classic Vestal model, where upon a mode switch, it is pessimistically assumed that all tasks may simultaneously exceed their less pessimistic execution time estimations, or lo-WCETs. In this paper, a less pessimistic MC model is proposed for system designers to specify the maximum number of tasks that may simultaneously exceed their lo-WCETs. The applicability and schedulability of the classic EDF-VD scheduler under this newly proposed model are studied, and a new schedulability test is presented. Experiments demonstrate that, by applying the proposed model and new schedulability test, significantly better schedulability can be achieved.