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

2. 2 Fabiano.Hessel@pucrs.br Introduction – Quality of Service oIncrease demand for embedded multimedia platforms (health devices, cellphones,…) oEnd-to-end QoS has become harder l new requirements imposed by multimedia systems and new codification techniques have emerged oQoS requirements has become essential oQuality of Service (QoS) l Offer Guarantees Bandwidth Delay Jitter Deadline miss rate

3. 3 Fabiano.Hessel@pucrs.br Introduction – QoS for Operating Systems oMapping l What? oAdmission Test l When? oResource Reservation Protocol l How? oIn a end-to-end manner. l Some applications demand end-to-end predictability. l Each part of a Operating System can (or should) take part in the end-to-end quality provision.

4. 4 Fabiano.Hessel@pucrs.br Motivation oFlexibility and predictability are desirable for applications and can be accomplished through end-to- end QoS provision. oThe Process Scheduler of an OS is a key player for QoS provision. oCurrent solutions do not offer hard real-time coexistence support with other task classes.

5. 5 Fabiano.Hessel@pucrs.br Job and Task Models oTask is a set of Jobs oEach Job has a Release time, Execution time, Relative deadline and Absolute deadline

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

7. 7 Fabiano.Hessel@pucrs.br R-EDF – Reservation Based EDF oA task reserves Θ(T), its mean utilization. oThe overrun state protects the system. oA job enters the overrun state when its reservation is reached. oAdmission control is limited by ΣΘ(T) <= 1.

8. 8 Fabiano.Hessel@pucrs.br R-EDF – Reservation Based EDF CPU Reservation: R-EDF has room for improvement: l Better performance for soft real-time tasks. l Support for hard real-time tasks.

9. 9 Fabiano.Hessel@pucrs.br ER-EDF – Enhanced R-EDF oBased on R-EDF oIncludes: l Hard real-time support l Improved performance for soft real-time tasks oComponents: l Admission Control Algorithm l Scheduling Algorithm

10. 10 Fabiano.Hessel@pucrs.br ER-EDF – Admission Control  β = 0.1  T A : θ=0.5 (1/2), Ψ =0.66 (2/3)  T B : θ=0.33 (1/3), Ψ =0.66 (2/3) TaskER-EDF Authorized? Overloaded - C RT = 0 PC RT = 0 C TS = 1 -No A C RT = 0.5 PC RT = 0.66 C TS = 0.5 YesNo A + B C RT = 0.83 PC RT = 1.32 C TS = 0.17 Yes A + B H C RT = 1.16 PC RT = 1.32 C TS = -0.16 NoYes

11. 11 Fabiano.Hessel@pucrs.br ER-EDF – Scheduling

12. 12 Fabiano.Hessel@pucrs.br System Architecture - SoC oSoC l Xilinx Spartan-3 FPGA l MIPS processor + EPOS l Serial l Display l SRAM (1 MB) l Internal Memory (8 KB) Internal Memory

13. 13 Fabiano.Hessel@pucrs.br Experiment - First

14. 14 Fabiano.Hessel@pucrs.br Experiment - First

15. 15 Fabiano.Hessel@pucrs.br Experiment - Second

16. 16 Fabiano.Hessel@pucrs.br Experiment - Second

17. 17 Fabiano.Hessel@pucrs.br Conclusions oScheduling plays a important role in QoS provision. oA new scheduler, ER-EDF was introduced. l Support for hard real-time tasks. l Better performance for soft real-time tasks when compared to its predecessor. l Fallback to classic EDF when the system is underloaded. oThe algorithm allows the developer to parameterize the OS to fulfill applications requirements, allowing flexibility and predictability.

18. 18 Thank You Questions?