Abstract
Allocation of bandwidth among components is a fundamental problem in compositional real-time systems. State-of-the-art algorithms for bandwidth allocation use either exponential-time or pseudo-polynomial-time techniques for exact allocation, or linear-time, utilization-based techniques which may over-provision bandwidth. In this paper, we propose research into a third possible approach: parametric approximation algorithms for bandwidth allocation in compositional real-time systems. We develop a fully-polynomial-time approximation scheme (FPTAS) for allocating bandwidth for sporadic task systems scheduled by earliest-deadline first (EDF) upon an Explicit-Deadline Periodic (EDP) resource. Our algorithm takes, as parameters, the task system and an accuracy parameter ϵ>0, and returns a bandwidth which is guaranteed to be at most a factor (1+ϵ) more than the optimal minimum bandwidth required to successfully schedule the task system. Furthermore, the algorithm has time complexity that is polynomial in the number of tasks and 1/ϵ.
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Notes
Note the component-level scheduling algorithm may differ from the system-level scheduling algorithm. Furthermore, many compositional frameworks permit components to be composed of sub-components.
We abuse terminology slightly and allow (Π,Θ,Δ) describe both the resource Ω and an interface for C.
Observe this is not a restriction on the number of hierarchical levels for our results. Subcomponents may also be represented by sporadic tasks, and our results will apply without change.
Please note that we are permitting over-capacity periodic resources for the sake of comparison only. Our goal is to show that the value returned by application of Theorem 2 (when such value exists) is bounded by a constant factor from the optimal Θ ∗. Showing that a solution for the relaxed problem (where over-capacity is permitted) is bounded by constant factor from optimal will imply the same for the original problem, where over-capacity periodic resources are disallowed.
Relative error is defined as follows: \(\frac{\varTheta-\varTheta^{*}}{\varTheta^{*}}\). In this case, the exact capacity is Θ ∗ and the estimated capacity Θ is either the sufficient capacity \(\bar{\varTheta}\) or approximate capacity \(\widehat {\varTheta}\).
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Acknowledgements
We are sincerely thankful to the reviewers for the detailed comments, corrections, and insightful directions which helped us to improve the quality of the article. This research has been supported in part by a National Science Foundation CAREER Award (CNS-0953585) and a grant from Wayne State University’s Office of Vice President of Research.
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A preliminary version of this work has been published in 21st Euromicro Conference on Real-Time Systems, 2009, pages 87–96 (Fisher and Dewan 2009).
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Fisher, N., Dewan, F. A bandwidth allocation scheme for compositional real-time systems with periodic resources. Real-Time Syst 48, 223–263 (2012). https://doi.org/10.1007/s11241-011-9144-7
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DOI: https://doi.org/10.1007/s11241-011-9144-7