SParK: An Integrated Real-Time System

1. SParK: An Integrated Real-Time System Vibhooti Verma 05305016

2. Outline • Introduction • SParK: System Requirements • SParK: Design Issues • Related Work on Scheduling • Our Proposed Modifications to Static & Dynamic Scheduling to consider: • Blocking factor • Aperiodic tasks • Conclusions and Further Work

3. Introduction to Integrated Real-Time Systems (IRTS) • Applications with different levels of criticality • Hard real-time • Soft real-time • Non real-time • Tasks with different arrival patterns • Aperiodic • Periodic • Spatial and Temporal partitioning

4. Motivation • Fault Containment • Easy Verification and Validation • Application Specific Operating System • Local Schedulability Analysis • Efficient Utilization of Resources

5. Basic Terms • Virtual slow processor • Constant Bandwidth Server (CBS) • Total Bandwidth Server (TBS) • Partition • Hierarchical Scheduling

6. SParK: System Requirements • Strongly partitioned architecture • Temporal and Spatial partitioning • Multiplex system resources among different partitions • Support partitions with different RTOS • Inter-Partition Communication • Simple design • Diskless system

7. SParK: Design Issues • Virtualization • Interrupts • I/O Devices • Processor • Memory • Timer • Partition Scheduling • Inter Partition Communication

8. SParK: System Architecture

9. SParK: Design Issues • Interrupt Handling • Requirement: To guarantee min. ‘n’ number of interrupts, if not all, in a particular partition will be served with bounded delay at any given point of time • Proposed Approach:Interrupt Bandwidth Server

10. SParK: Design Issues • I/O Virtualization

11. Existing work in IRTS Scheduling • Open Environment ‘s Dynamic-Priority-Driven (EDF) Scheduling • CBS & TBS for scheduling partitions • Handling Aperiodic tasks not clear • Handling Blocking factor with TBS only • SPIRIT’s Cyclic Scheduling • Non-preemptable sections not handled

12. Our Scheduling Strategies • CBS: Failure to Handle Non-preemptable(NP) Sections

13. Our Scheduling Strategies • Handling NP Sections: CBS with Budget Lending • Modified schedulability bound: • Modified server size: where is the maximum blocking duration N - total number of applications in the system Lj - is longest critical section in Pj - relative shortest deadline in partition Pj

14. Our Scheduling Strategies • CBS with Budget Lending: Example

15. Our Scheduling Strategies • Handling Hard Aperiodic Tasks in TBS provides no guarantee • Handling Hard Aperiodic Tasks in CBS • Dedicated Aperiodic Server • Online Acceptance Test • Algorithm-1: Schedules them as early as possible • Poor responsiveness to soft aperiodic tasks • High acceptance ratio for hard aperiodic tasks • Algorithm-2: Schedules them as late as possible • Better responsiveness to soft aperiodic tasks • Low acceptance ratio for hard aperiodic tasks

16. Comparisons of Algorithms • Algorithm 2 gives better responsiveness to Soft Aperiodic Tasks

17. Our Scheduling Strategies • Comparison of Algorithm1 and Algorithm2: Algorithm 2 gives better responsiveness to Soft Aperiodic Tasks Algorithm-1 Algorithm-2

18. Comparisons of Algorithms • Algorithm 1 gives higher acceptance ratio for hard aperiodic tasks

19. Comparisons of Algorithms Algorithm-1 Algorithm-2

20. Cyclic Scheduling • Handling Aperiodic Tasks -dedicated partition for aperiodic task -left sliding -right putting • Handling Non-preemptable section • no provision -may lead to deadline miss of tasks in some partition.

21. Failure of Cyclic Scheduling to Handle NP Section

22. Our Scheduling Strategies • Handling NP Sections: Blocked Partition lend their budget to blocking partition • Modified schedulability bound: • Modified server size: where is the maximum blocking duration N - total number of applications in the system Lj - is longest critical section in Pj - relative shortest deadline in partition Pj

23. Static Scheduling with budget Lending

24. Open System Vs Cyclic Scheduling

25. VM Environment Vs SParK

26. Conclusions • Analogies are drawn between VM environment and SParK • Partial design of SParK is presented • Proposed modifications to (dynamic & static) scheduling algorithms to consider: • Blocking factor • Aperiodic tasks • Proposed strategies for handling interrupts

27. Future Work • Detailed analysis of: • Interrupt handling • Aperiodic tasks and Blocking factor • Timekeeping • Memory management • Prototype of the system

28. References • Daeyoung Kim. Strongly Partitioned System Architecture For Integration Of Real-Time Applications. PhD thesis, UNIVERSITY OF FLORIDA, 2001 • Zhong Deng, Jane W.-S. Liu, Lynn Zhang, Seri Mouna, and Alban Frei. An open environment for real-time applications. Real-Time Systems, 16(2-3):155{185, 1999 • Mendel Rosenblum and Tal Garnkel. Virtual machine monitors: Current technology and future trends. IEE Computer Magazine, May 2005 • Tullio Facchinetti, Giorgio Buttazzo, Mauro Marinoni, and Giacomo Guidi. Non-preemptive interrupt scheduling for safe reuse of legacy drivers in real-time systems. In ECRTS '05, pages 98-105, Washington, DC, USA, 2005. IEEE Computer Society • Paul Barham, Boris Dragovic, Keir Fraser, Steven Hand, Tim Harris, Alex Ho, Rolf Neugebauer, Ian Pratt, and Andrew Wareld. Xen and the art of virtualization. In SOSP '03, pages 164{177, New York, NY, USA, 2003. ACM Press