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A Reservation Scheduler for Real-Time Operating Systems

A Reservation Scheduler for Real-Time Operating Systems. David Matschulat, César Marcon, Fabiano Hessel PUCRS - Brazil. Introduction – Quality of Service. Increase demand for embedded multimedia platforms (health devices, cellphones,…) End-to-end QoS has become harder

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A Reservation Scheduler for Real-Time Operating Systems

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  1. A Reservation Scheduler for Real-Time Operating Systems David Matschulat, César Marcon, Fabiano Hessel PUCRS - Brazil

  2. Introduction – Quality of Service • Increase demand for embedded multimedia platforms (health devices, cellphones,…) • End-to-end QoS has become harder • new requirements imposed by multimedia systems and new codification techniques have emerged • QoS requirements has become essential • Quality of Service (QoS) • Offer Guarantees • Bandwidth • Delay • Jitter • Deadline miss rate

  3. Introduction – QoS for Operating Systems • Mapping • What? • Admission Test • When? • Resource Reservation Protocol • How? • In a end-to-end manner. • Some applications demand end-to-end predictability. • Each part of a Operating System can (or should) take part in the end-to-end quality provision.

  4. Motivation • Flexibility and predictability are desirable for applications and can be accomplished through end-to-end QoS provision. • The Process Scheduler of an OS is a key player for QoS provision. • Current solutions do not offer hard real-time coexistence support with other task classes.

  5. Job and Task Models • Task is a set of Jobs • Each Job has a Release time, Execution time, Relative deadline and Absolute deadline

  6. R-EDF – Reservation Based EDF • β = Best-effort Reservation • Θ(J) = Job Utilization • Θ(T) = Task Utilization: the mean utilization of all jobs. • Ψ(T) = Peak Utilization: the utilization of its largest job. • PCRT = Peak Capacity: sum of the peaks (Ψ) of all jobs of a task. • The system is overloaded when PCRT > 1 – β.

  7. R-EDF – Reservation Based EDF • A task reserves Θ(T), its mean utilization. • The overrun state protects the system. • A job enters the overrun state when its reservation is reached. • Admission control is limited by ΣΘ(T) <= 1.

  8. R-EDF – Reservation Based EDF CPU Reservation: R-EDF has room for improvement: • Better performance for soft real-time tasks. • Support for hard real-time tasks.

  9. ER-EDF – Enhanced R-EDF • Based on R-EDF • Includes: • Hard real-time support • Improved performance for soft real-time tasks • Components: • Admission Control Algorithm • Scheduling Algorithm

  10. ER-EDF – Admission Control • β= 0.1 • TA: θ=0.5 (1/2), Ψ=0.66 (2/3) • TB: θ=0.33 (1/3), Ψ=0.66 (2/3)

  11. ER-EDF – Scheduling

  12. Internal Memory System Architecture - SoC • SoC • Xilinx Spartan-3 FPGA • MIPS processor + EPOS • Serial • Display • SRAM (1 MB) • Internal Memory (8 KB)

  13. Experiment - First

  14. Experiment - First

  15. Experiment - Second

  16. Experiment - Second

  17. Conclusions • Scheduling plays a important role in QoS provision. • A new scheduler, ER-EDF was introduced. • Support for hard real-time tasks. • Better performance for soft real-time tasks when compared to its predecessor. • Fallback to classic EDF when the system is underloaded. • The algorithm allows the developer to parameterize the OS to fulfill applications requirements, allowing flexibility and predictability.

  18. Thank YouQuestions?

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