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Bounding and shaping the demand of generalized mixed-criticality sporadic task systems
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. (Embedded Systems)
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. (Embedded Systems)
2014 (English)In: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 50, no 1, 48-86 p.Article in journal (Refereed) Published
Abstract [en]

We generalize the commonly used mixed-criticality sporadic task model to let all task parameters (execution-time, deadline and period) change between criticality 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 formulate 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 characteristics 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 thecomputing platform. Experiments indicate that this approach is successful in practice. This new approach has the added benefit of supporting hierarchical scheduling frameworks.

Place, publisher, year, edition, pages
2014. Vol. 50, no 1, 48-86 p.
National Category
Computer Science
Research subject
Computer Science with specialization in Real Time Systems
Identifiers
URN: urn:nbn:se:uu:diva-212779DOI: 10.1007/s11241-013-9187-zISI: 000328351200003OAI: oai:DiVA.org:uu-212779DiVA: diva2:679216
Projects
UPMARC
Available from: 2013-06-15 Created: 2013-12-13 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Models and Complexity Results in Real-Time Scheduling Theory
Open this publication in new window or tab >>Models and Complexity Results in Real-Time Scheduling Theory
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

When designing real-time systems, we want to prove that they will satisfy given timing constraints at run time. The main objective of real-time scheduling theory is to analyze properties of mathematical models that capture the temporal behaviors of such systems. These models typically consist of a collection of computational tasks, each of which generates an infinite sequence of task activations. In this thesis we study different classes of models and their corresponding analysis problems.

First, we consider models of mixed-criticality systems. The timing constraints of these systems state that all tasks must meet their deadlines for the run-time scenarios fulfilling certain assumptions, for example on execution times. For the other scenarios, only the most important tasks must meet their deadlines. We study both tasks with sporadic activation patterns and tasks with complicated activation patterns described by arbitrary directed graphs. We present sufficient schedulability tests, i.e., methods used to prove that a given collection of tasks will meet their timing constraints under a particular scheduling algorithm.

Second, we consider models where tasks can lock mutually exclusive resources and have activation patterns described by directed cycle graphs. We present an optimal scheduling algorithm and an exact schedulability test.

Third, we address a pair of longstanding open problems in real-time scheduling theory. These concern the computational complexity of deciding whether a collection of sporadic tasks are schedulable on a uniprocessor. We show that this decision problem is strongly coNP-complete in the general case. In the case where the asymptotic resource utilization of the tasks is bounded by a constant smaller than 1, we show that it is weakly coNP-complete.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 32 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1324
Keyword
Real-time systems, Scheduling theory, Task models, Computational complexity
National Category
Computer Science
Research subject
Computer Science with specialization in Embedded Systems
Identifiers
urn:nbn:se:uu:diva-267017 (URN)978-91-554-9423-0 (ISBN)
Public defence
2016-01-15, ITC, 2446, Lägerhyddsvägen 2, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2015-12-16 Created: 2015-11-16 Last updated: 2016-01-13

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Ekberg, PontusYi, Wang

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