Multiprocessor Fixed Priority Scheduling with Limited Preemptions

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Author(s)

  • Abhilash Thekkilakattil
  • Robert Ian Davis
  • Radu Dobrin
  • Sasikumar Punnekkat
  • Marko Bertogna

Department/unit(s)

Publication details

Title of host publicationRTNS '15
DatePublished - Nov 2015
Pages13-22
PublisherACM
Original languageEnglish
ISBN (Print)978-1-4503-3591-1

Abstract

Challenges associated with allowing preemptions and migrations are compounded in multicore systems, particularly under global scheduling policies, because of the potentially high overheads. For example, multiple levels of cache greatly increase preemption and migration related overheads as well as the difficulty involved in accurately accounting for them, leading to substantially inflated
worst-case execution times (WCETs). Preemption and migration related overheads can be significantly reduced, both in number and in size, by using fixed preemption points in the tasks’ code; thus dividing each task into a series of non-preemptive regions (NPRs). This leads to an additional consideration in the scheduling policy. When a high priority task is released and all of the processors are executing non-preemptive regions of lower priority tasks, then there is a choice to be made in terms of how to manage the next preemption. With an eager approach the first lower priority task to reach a preemption point is preempted even if it is not the lowest priority running task. Alternatively, with a lazy approach, preemption is delayed until the lowest priority currently running task reaches its next preemption point.
In this paper, we show that under global fixed priority scheduling with eager preemptions each task suffers from at most a single priority inversion each time it resumes execution. Building on this observation, we derive a new response time based schedulability test for tasks with fixed preemption points. Experimental evaluations show that global fixed priority scheduling with eager preemptions is significantly more effective than with lazy preemption using link based scheduling in terms of task set schedulability.

    Research areas

  • limited preemption, multiprocessor scheduling, REAL-TIME SYSTEMS

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