4,442 research outputs found
Scheduling policies and system software architectures for mixed-criticality computing
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
Analysis and Optimization of Mixed-Criticality Applications on Partitioned Distributed Architectures
Schedulability analysis and optimization of time-partitioned distributed real-time systems
RESUMEN: La creciente complejidad de los sistemas de control modernos lleva a muchas empresas a tener que re-dimensionar o re-diseñar sus soluciones para adecuarlas a nuevas funcionalidades y requisitos. Un caso paradigmático de esta situación se ha dado en el sector ferroviario, donde la implementación de las aplicaciones de señalización se ha llevado a cabo empleando técnicas tradicionales que, si bien ahora mismo cumplen con los requisitos básicos, su rendimiento temporal y escalabilidad funcional son sustancialmente mejorables. A partir de las soluciones propuestas en esta tesis, además de contribuir a la validación de sistemas que requieren certificación de seguridad funcional, también se creará la tecnologÃa base de análisis de planificabilidad y optimización de sistemas de tiempo real distribuidos generales y también basados en particionado temporal, que podrá ser aplicada en distintos entornos en los que los sistemas ciberfÃsicos juegan un rol clave, por ejemplo en aplicaciones de Industria 4.0, en los que pueden presentarse problemas similares en el futuro.ABSTRACT:he increasing complexity of modern control systems leads many companies to have to resize or redesign their solutions to adapt them to new functionalities and requirements. A paradigmatic case of this situation has occurred in the railway sector, where the implementation of signaling applications has been carried out using traditional techniques that, although they currently meet the basic requirements, their time performance and functional scalability can be substantially improved. From the solutions proposed in this thesis, besides contributing to the assessment of systems that require functional safety certification, the base technology for schedulability analysis and optimization of general as well as time-partitioned distributed real-time systems will be derived, which can be applied in different environments where cyber-physical systems play a key role, for example in Industry 4.0 applications, where similar problems may arise in the future
k2U: A General Framework from k-Point Effective Schedulability Analysis to Utilization-Based Tests
To deal with a large variety of workloads in different application domains in
real-time embedded systems, a number of expressive task models have been
developed. For each individual task model, researchers tend to develop
different types of techniques for deriving schedulability tests with different
computation complexity and performance. In this paper, we present a general
schedulability analysis framework, namely the k2U framework, that can be
potentially applied to analyze a large set of real-time task models under any
fixed-priority scheduling algorithm, on both uniprocessor and multiprocessor
scheduling. The key to k2U is a k-point effective schedulability test, which
can be viewed as a "blackbox" interface. For any task model, if a corresponding
k-point effective schedulability test can be constructed, then a sufficient
utilization-based test can be automatically derived. We show the generality of
k2U by applying it to different task models, which results in new and improved
tests compared to the state-of-the-art.
Analogously, a similar concept by testing only k points with a different
formulation has been studied by us in another framework, called k2Q, which
provides quadratic bounds or utilization bounds based on a different
formulation of schedulability test. With the quadratic and hyperbolic forms,
k2Q and k2U frameworks can be used to provide many quantitive features to be
measured, like the total utilization bounds, speed-up factors, etc., not only
for uniprocessor scheduling but also for multiprocessor scheduling. These
frameworks can be viewed as a "blackbox" interface for schedulability tests and
response-time analysis
Resource-Efficient Scheduling Of Multiprocessor Mixed-Criticality Real-Time Systems
Timing guarantee is critical to ensure the correctness of embedded software systems that
interact with the physical environment. As modern embedded real-time systems evolves,
they face three challenges: resource constraints, mixed-criticality, and multiprocessors. This
dissertation focuses on resource-efficient scheduling techniques for mixed-criticality systems
on multiprocessor platforms.
While Mixed-Criticality (MC) scheduling has been extensively studied on uniprocessor plat-
forms, the problem on multiprocessor platforms has been largely open. Multiprocessor al-
gorithms are broadly classified into two categories: global and partitioned. Global schedul-
ing approaches use a global run-queue and migrate tasks among processors for improved
schedulability. Partitioned scheduling approaches use per processor run-queues and can
reduce preemption/migration overheads in real implementation. Existing global scheduling
schemes for MC systems have suffered from low schedulability. Our goal in the first work is
to improve the schedulability of MC scheduling algorithms. Inspired by the fluid scheduling
model in a regular (non-MC) domain, we have developed the MC-Fluid scheduling algo-
rithm that executes a task with criticality-dependent rates. We have evaluated MC-Fluid in
terms of the processor speedup factor: MC-Fluid is a multiprocessor MC scheduling algo-
rithm with a speed factor of 4/3, which is known to be optimal. In other words, MC-Fluid
can schedule any feasible mixed-criticality task system if each processor is sped up by a
factor of 4/3.
Although MC-Fluid is speedup-optimal, it is not directly implementable on multiprocessor
platforms of real processors due to the fractional processor assumption where multiple task
can be executed on one processor at the same time. In the second work, we have considered
the characteristic of a real processor (executing only one task at a time) and have developed
the MC-Discrete scheduling algorithm for regular (non-fluid) scheduling platforms. We have
shown that MC-Discrete is also speedup-optimal.
While our previous two works consider global scheduling approaches, our last work con-
siders partitioned scheduling approaches, which are widely used in practice because of low
implementation overheads. In addition to partitioned scheduling, the work consid-
ers the limitation of conventional MC scheduling algorithms that drops all low-criticality
tasks when violating a certain threshold of actual execution times. In practice, the system
designer wants to execute the tasks as much as possible. To address the issue, we have de-
veloped the MC-ADAPT scheduling framework under uniprocessor platforms to drop as few
low-criticality tasks as possible. Extending the framework with partitioned multiprocessor
platforms, we further reduce the dropping of low-criticality tasks by allowing migration of
low-criticality tasks at the moment of a criticality switch. We have evaluated the quality
of task dropping solution in terms of speedup factor. In existing work, the speedup factor
has been used to evaluate MC scheduling algorithms in terms of schedulability under the
worst-case scheduling scenario. In this work, we apply the speedup factor to evaluate MC
scheduling algorithms in terms of the quality of their task dropping solution under various
MC scheduling scenarios. We have derived that MC-ADAPT has a speedup factor of 1.618
for task dropping solution
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