Abstract
Harmonic periods have been of great importance in the design of real-time applications due to their high schedulability, predictability, and ease of analysis. Therefore, period assignment is an important part of the design process of many real-time systems. This includes various applications such as radar dwell tasks, robotics, and industrial control applications, where tasks are specified using period ranges and worst-case execution times. In this paper, we study the issue of assigning a fixed number of harmonic periods from period ranges to maximize utilization in real-time systems. In the existing period assignment approaches, the number of different harmonic period values in the solution was not addressed. In this work, we show that, in real-time systems in which the number of available task periods is restricted, such a constraint is crucial for efficient system design. We formally define the problem in the context of existing harmonic period assignment research. We show that this problem is at least weakly NP-hard and devise an optimal algorithm and suboptimal heuristics. Based on an extensive evaluation on synthetically generated task sets, we conclude that our approach is efficient and applicable in a variety of real-world scenarios.
Highlights
In traditional industrial control systems, timeliness, stability and predictability are very important properties
As the parameters used for synthetically generating task sets correspond to the parameters of task sets in motivational scenarios, we show that our approach can be efficiently used in plenty of real-world scenarios
EVALUATION IN THE CONTEXT OF EXISTING utilization-maximizing harmonic period assignment (UHPA) APPROACHES On the basis of Theorem IV.1, we know that the UHPA problem is Turing reducible to the UDHPA problem, and we can employ our optimal algorithm for UHPA instances
Summary
In traditional industrial control systems, timeliness, stability and predictability are very important properties. The first research area includes papers focused on the schedulability of real-time systems with arbitrary period selection, i.e., periods of task sets are not constrained to harmonic values. Research in this context was done by Seto at al. The authors devised algorithms for discovering feasible integer periods in fixed-priority systems with a fixed rate-monotonic and an arbitrary priority assignment In their approach periods are upper-bounded by the slowest task rate required by an application. We devise an optimal and heuristic algorithms for the UDHPA problem, provide time-complexity analysis, and show the effectiveness of the approach with extensive evaluation on a large number of synthetically generated instances, which correspond to real-world motivational scenarios (iii).
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