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Exact comparison of fixed priority and EDF scheduling based on speedup factors for both pre-emptive and non-pre-emptive paradigms

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Abstract

This paper investigates the relative effectiveness of fixed priority (FP) scheduling in a uniprocessor system compared to earliest deadline first (EDF) scheduling. The quantitative metric used in this comparison is the processor speedup factor, defined as the factor by which processor speed needs to increase to ensure that any task set that is schedulable according to EDF can be scheduled using fixed priorities. In the pre-emptive case, exact speedup factors are known for sporadic task sets with implicit or constrained deadlines. In this paper, we derive exact speedup factors for both pre-emptive and non-pre-emptive fixed priority scheduling of arbitrary deadline sporadic task sets. We also show that the exact speedup factor for the pre-emptive case holds when tasks share resources according to the stack resource policy/deadline floor protocol.

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Notes

  1. A task set is synchronous if all of its tasks share a common release time.

  2. Deadline monotonic priority ordering assigns priorities in order of task deadlines, such that the task with the shortest deadline is given the highest priority.

  3. This algorithm is optimal in the sense that it finds a schedulable priority ordering whenever such an ordering exists.

  4. An algorithm is work-conserving if it never idles the processor when there is a job ready to execute.

  5. A periodic task set is referred to as non-concrete if the times at which each task is first released are unknown, also sometimes referred to as having arbitrary phasing.

  6. Sporadic task sets represent a generalisation of non-concrete periodic task sets.

  7. By a class of algorithm we mean for example pre-emptive scheduling algorithms.

  8. Recall, we assume discrete time, with granularity \(\Delta \).

  9. Recall that a periodic task set is referred to as non-concrete if the times at which each task is first released are unknown.

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Acknowledgments

This work was funded in part by the EPSRC Projects TEMPO (EP/G055548/1) and MCC (EP/K011626/1). EPSRC Research Data Management: No new primary data was created during this study.

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Authors and Affiliations

  1. Real-Time Systems Research Group, Department of Computer Science, University of York, York, UK

    Robert I. Davis, Alan Burns & Oliver Gettings

  2. AOSTE Team, INRIA, Paris-Rocquencourt, France

    Robert I. Davis

  3. Department of Computer Science, University of North Carolina, Chapel Hill, NC, 27599-317, USA

    Sanjoy Baruah

  4. Department of Mathematics, University of Washington, Seattle, WA, USA

    Thomas Rothvoß

  5. Universite Paris-Est, LIGM, ESIEE, Paris, France

    Laurent George

Authors
  1. Robert I. Davis
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  2. Alan Burns
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  3. Sanjoy Baruah
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  4. Thomas Rothvoß
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  5. Laurent George
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  6. Oliver Gettings
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Correspondence to Robert I. Davis.

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Davis, R.I., Burns, A., Baruah, S. et al. Exact comparison of fixed priority and EDF scheduling based on speedup factors for both pre-emptive and non-pre-emptive paradigms. Real-Time Syst 51, 566–601 (2015). https://doi.org/10.1007/s11241-015-9233-0

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