Overrun and Skipping in Hierarchically Scheduled Real-Time Systems.
ABSTRACT Recently, two SRP-based synchronization protocols for hierarchically scheduled real-time systems based on fixed priority preemptive scheduling (FPPS) have been presented, i.e., HSRP and SIRAP. Preventing depletion of budget during global resource access, the former implements an overrun mechanism, while the later exploits a skipping mechanism. A theoretical comparison of the performance of these mechanisms revealed that none of them was superior to the other, as their performance is heavily dependent on the system's parameters. To better understand the relative strengths and weaknesses of these mechanisms, this paper presents a comparative evaluation of the depletion prevention mechanisms overrun (with or without payback) and skipping. These mechanisms are investigated in detail and the corresponding system load imposed by these mechanisms is explored in a simulation study. The mechanisms are evaluated assuming FPPS and a periodic resource model. The periodic resource model is selected as it supports locality of schedulability analysis, allowing for a truthful comparison of the mechanisms. Given system characteristics, guiding the design of hierarchically scheduled real-time systems, the results of this paper indicate when one mechanism is better than the other and how a system should be configured in order to operate efficiently.
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ABSTRACT: Hierarchical scheduling frameworks (HSFs) provide means for composing complex real-time systems from well-defined independently developed and analyzed subsystems. To support shared logical resources requiring mutual exclusive access in two-level HSFs, overrun without payback has been proposed as a mechanism to prevent budget depletion during resource access arbitrated by the stack resource policy (SRP). In this paper, we revisit the global schedulability analysis of synchronization protocols based on SRP and overrun without payback for fixed-priority scheduled HSFs. We derive a new global schedulability analysis based on the observation that the overrun budget is merely meant to prevent budget depletion during global resource access. The deadline of a subsystem therefore only needs to hold for its normal budget rather than the sum of the normal and overrun budget. Our novel analysis is considerably simpler than an earlier, initially improved analysis, which improved both the original local and global schedulability analyses. We evaluate the new analysis based on an extensive simulation study and compare the results with the existing analysis. Our simplified analysis does not significantly affect schedulability compared to the initially improved analysis. It is therefore proposed as a preferable engineering approach to synchronization protocols for compositional real-time systems. We accordingly present the implementation of our improvement in an OSEK-compliant real-time operating system to sketch its applicability in today's industrial automotive standards. Both implementation and run-time overheads are discussed providing measured results.Industrial Embedded Systems (SIES), 2011 6th IEEE International Symposium on; 07/2011
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ABSTRACT: In this paper, we show that both global as well as local schedulability analysis of synchronization protocols based on the stack resource policy (SRP) and overrun without payback for hierarchical scheduling frameworks based on fixed-priority preemptive scheduling (FPPS) are pessimistic. We present tighter global and local schedulability analysis, illustrate the improvements of the new analysis by means of examples, and show that the improved global analysis is both uniform and sustainable. We evaluate the new global and local schedulability analysis based on an extensive simulation study and compare the results with the existing analysis.Engineering of Complex Computer Systems (ICECCS), 2011 16th IEEE International Conference on; 05/2011
Conference Paper: Constant-bandwidth supply for priority processing[Show abstract] [Hide abstract]
ABSTRACT: Today's consumer electronic devices feature multiple applications which have to share scarcely available resources. We consider a priority-processing-based video application, which comprises multiple scalable video algorithms (SVAs) that are executed on a shared, virtual platform. This application is given a guaranteed processor share by means of a constant-bandwidth server (CBS), which in addition efficiently reclaims all spare processor time. A decision scheduler distributes the assigned processor share among the SVAs, with the aim to maximize their overall output quality. To correctly distribute this processor share we introduce the concept of a virtual timer. This timer only advances when its associated virtual platform is executing.Consumer Electronics (ICCE), 2011 IEEE International Conference on; 02/2011