Generalized Fixed-Priority Scheduling with Limited Preemptions

Bril, Reinder J.; Heuvel, Martijn van den; Keskin, Ugur; Lukkien, Johan J.

doi:10.1109/ecrts.2012.34

Cited by 15 publications

(36 citation statements)

References 20 publications

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“…The results are compared with the scheduling analysis ignoring CRPD. We have therefore generated system configurations so that the results for FPTS without CRPD match those in [10,15] and the results for FPPS with CRPD those in [3].…”

Section: Discussionmentioning

confidence: 99%

“…tasks are non-pre-emptive and therefore experience minimal CRPD. The algorithm traverses the tasks in descending priority order (lines [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. When it considers a task τ i , it first assigns its maximum pre-emption threshold θ i to θ i (line 7).…”

mentioning

confidence: 99%

“…Next, it tests schedulability of τ i without any blocking and returns unschedulable when the test fails (line 9). Otherwise, it tests schedulability of τ i with blocking by considering each lower priority task τ in isolation (lines [11][12][13][14][15][16][17][18][19][20][21][22]. It decreases the maximum pre-emption threshold θ of τ if-and-only-if τ i is unschedulable due to blocking by task τ (lines [17][18][19].…”

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confidence: 99%

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Integrating Cache-Related Pre-Emption Delays into Analysis of Fixed Priority Scheduling with Pre-Emption Thresholds

Bril

Altmeyer

Heuvel

et al. 2014

2014 IEEE Real-Time Systems Symposium

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Abstract-Cache-related pre-emption delays (CRPD) have been integrated into the schedulability analysis of sporadic tasks with constrained deadlines for fixed-priority pre-emptive scheduling (FPPS). This paper generalizes that work by integrating CRPD into the schedulability analysis of tasks with arbitrary deadlines for fixed-priority pre-emption threshold scheduling (FPTS). The analysis is complemented by an optimal threshold assignment algorithm that minimizes CRPD. The paper includes a comparative evaluation of the schedulability ratios of FPPS and FPTS, for constrained-deadline tasks, taking CRPD into account. I. IntroductionFor cost-effectiveness reasons, it is preferred to use commercial off-the-shelf (COTS) programmable platforms for real-time embedded systems, rather than dedicated, application-domain specific platforms. These COTS platforms typically contain a cache to bridge the gap between the processor speed and main memory speed and to reduce the number of conflicts with other devices on the system bus. Unfortunately, caches give rise to additional delays upon pre-emptions due to cache flushes and reloads of blocks that are replaced during pre-emption. This cache-related pre-emption delay (CRPD) can have a significant impact on the computation times of tasks. For fixed-priority pre-emptive scheduling (FPPS), which is the defacto standard used in industry, CRPD has therefore been integrated into the schedulability analysis [17,26,32,28,3].Recently, limited pre-emptive scheduling schemes received a lot of attention from academia. In particular, fixed-priority scheduling with limited pre-emptions, such as fixed-priority scheduling with deferred pre-emption (FPDS) or co-operative scheduling [16,14,20] and fixed-priority scheduling with preemption thresholds (FPTS) [33,31,30,25], are considered viable alternatives between the extremes of FPPS and fixedpriority non-pre-emptive scheduling (FPNS). Compared to FPPS, limited pre-emptive schemes can (i) reduce memory requirements [31,23,21] and (ii) reduce the cost of arbitrary pre-emptions [16,14,10]. Compared to both FPPS and FPNS, these schemes may significantly improve the feasibility of a task set [14,31,8,20].Although FPDS clearly outperforms FPTS from a theoretical perspective [18], applying FPDS in practice is still a challenge because pre-emption points have to be explicitly added in the code. Assuming strictly periodic tasks with known phasing, a single non-pre-emptive region (NPR) can significantly reduce the preemptions that can feasibly occur [29]. Alternatively, sporadic tasks with floating NPRs [34,6] can be used; however, these require specific operating-system support and can lead

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Section: Discussionmentioning

confidence: 99%

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Integrating Cache-Related Pre-Emption Delays into Analysis of Fixed Priority Scheduling with Pre-Emption Thresholds

Bril

Altmeyer

Heuvel

et al. 2014

2014 IEEE Real-Time Systems Symposium

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“…In [69], [61] Saksena and Wang attempted to derive an integrated approach to priority and pre-emption threshold assignment, but did not succeed in finding an optimal algorithm with less than exponential complexity. Research by Bril et al [18] in 2012 combines the ideas of deferred pre-emption and pre-emption thresholds, generalising both into a single scheme with pre-emption thresholds between a set of sub-jobs which execute non-preemptively.…”

Section: Limiting Pre-emptionmentioning

confidence: 99%

A review of fixed priority and EDF scheduling for hard real-time uniprocessor systems

Davis

2014

SIGBED Rev.

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This paper was written to accompany a talk at the ETR Summer School in Toulouse 2013. It provides a background and primer to scheduling and schedulability analysis for hard real-time single processor systems. The paper focuses on the two main scheduling algorithms used: Fixed Priority and Earliest Deadline First. The paper has two broad aims: Firstly to provide a guide to the fundamental results for these realtime scheduling algorithms. Secondly to provide a brief review of extensions aimed at (i) limiting the effects and overheads of pre-emption and (ii) accounting for the effects of preemptions; specifically cache related pre-emption delays. The paper also briefly looks back at success stories in real-time scheduling, and forwards at the current hot topics in this research area.

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“…Bril et al 2009;Bertogna et al 2011a, b;Davis and Bertogna 2012); (3) a combination of the two former approaches (e.g. Bril et al 2012). All these works target task scheduling on processors.…”

Section: Related Workmentioning

confidence: 99%

Using non-preemptive regions and path modification to improve schedulability of real-time traffic over priority-based NoCs

et al. 2017

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Network-on-Chip (NoC) is a preferred communication medium for massively parallel platforms. Fixed-priority based scheduling using virtual-channels is one of the promising solutions to support real-time traffic in on-chip networks. Most of the existing works regarding priority-based NoCs use a flit-level preemptive scheduling. Under such a mechanism, preemptions can only happen between the transmissions of successive flits but not during the transmission of a single flit. In this paper, we present a modified framework where the non-preemptive region of each NoC packet increases from a single flit. Using the proposed approach, the response times of certain traffic flows can be reduced, which can thus improve the schedulability of the whole network. As a result, the utilization of NoCs can be improved by admitting more real-time traffic. Schedulability tests regarding the proposed framework are presented along with the proof of the correctness. Additionally, we also propose a path modification approach on top of the non-preemptive region based method to further improve schedulability. A number of experiments have been performed to evaluate the proposed solutions, where we can observe significant improvement on schedulability compared to the original flit-level preemptive NoCs.This work is an extended version of the paper presented at RTCSA 2016 (Liu et al. 2016).

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Generalized Fixed-Priority Scheduling with Limited Preemptions

Cited by 15 publications

References 20 publications

Integrating Cache-Related Pre-Emption Delays into Analysis of Fixed Priority Scheduling with Pre-Emption Thresholds

Integrating Cache-Related Pre-Emption Delays into Analysis of Fixed Priority Scheduling with Pre-Emption Thresholds

A review of fixed priority and EDF scheduling for hard real-time uniprocessor systems

Using non-preemptive regions and path modification to improve schedulability of real-time traffic over priority-based NoCs

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