Course Matters

1. Course Matters

2. Paper Review Paper Reviews Due 20% off for each late day NUS.SOC.CS5248 OOI WEI TSANG

3. Diwali/Deepavali No Class NUS.SOC.CS5248 OOI WEI TSANG

4. Guest Lecture CS6212 Guest Lecture “A/V Synchronization” SR1 4-6pm NUS.SOC.CS5248 OOI WEI TSANG

5. Books NUS.SOC.CS5248 OOI WEI TSANG

6. Project Grading NUS.SOC.CS5248 OOI WEI TSANG

7. Previously, on CS5248

8. Cello • OS disk scheduler • Support multiple classes • Protect classes from each other • Work conserving • Use two-level scheduling NUS.SOC.CS5248 OOI WEI TSANG

9. CPU vs Disk Scheduling • Task computation time unpredictable • Task can be preemptive NUS.SOC.CS5248 OOI WEI TSANG

10. Problem • How can multimedia applications co-exists with normal applications? NUS.SOC.CS5248 OOI WEI TSANG

11. Same Old Idea NUS.SOC.CS5248 OOI WEI TSANG

12. Same Gang P. Goyal, X. Guo, and H. M. Vin. “A hierarchical CPU scheduler for multimedia operating systems.” OSDI’96 NUS.SOC.CS5248 OOI WEI TSANG

13. So Far Best-Effort Real-Time Scheduling NUS.SOC.CS5248 OOI WEI TSANG

14. How to Guarantee Services? NUS.SOC.CS5248 OOI WEI TSANG

15. Resource Reservation: CPU

16. Resource Reservations • How to reserve? • Overbook? • Overuse? NUS.SOC.CS5248 OOI WEI TSANG

17. Example: Memory • How to reserve? malloc • Overbook? return NULL • Overuse? crash, throw exception NUS.SOC.CS5248 OOI WEI TSANG

18. Example: Memory • How to reserve? “I will need 128KB” • Overbook? “Sorry!” • Overuse? malloc returns NULL NUS.SOC.CS5248 OOI WEI TSANG

19. Example: CPU • How to reserve? • Overbook? • Overuse? Memoryis discrete. CPUtimeis continuous. NUS.SOC.CS5248 OOI WEI TSANG

20. How to Reserve?

21. CPU Reservation • “I need C units of time, out of every T units.” NUS.SOC.CS5248 OOI WEI TSANG

22. Two Problems • How to determine C? • take measurement and estimate • What if C is not constant? • take the maximum NUS.SOC.CS5248 OOI WEI TSANG

23. Effects of T and C NUS.SOC.CS5248 OOI WEI TSANG

24. CPU Scheduling Algorithm

25. Classic Real-Time Scheduler

26. Rate Scheduling Algorithms • Rate Monotonic • Earliest Deadline First NUS.SOC.CS5248 OOI WEI TSANG

27. Rate Monotonic NUS.SOC.CS5248 OOI WEI TSANG

28. EDF NUS.SOC.CS5248 OOI WEI TSANG

29. Classic Schedulability Theorems • Rate Monotonic Scheduler • Earliest Deadline First NUS.SOC.CS5248 OOI WEI TSANG

30. Assumptions • programs are periodic • computation time is constant • zero context switch time • programs are independent NUS.SOC.CS5248 OOI WEI TSANG

31. Why do we care about RM? • Theoretically, RM has lower CPU utilization (70%) but • RM is more efficient than EDF • Can support up to 80-90% CPU utilization in practice • Don’t want to commit 100% CPU anyway (for emergency) NUS.SOC.CS5248 OOI WEI TSANG

32. Rialto Scheduler From MS Research

33. Overview • Given a set of task, pre-compute a scheduling graph NUS.SOC.CS5248 OOI WEI TSANG

34. B E A C B E D F B E A B E D NUS.SOC.CS5248 OOI WEI TSANG

35. C A B E F D NUS.SOC.CS5248 OOI WEI TSANG

36. Advantages • Only need to make new scheduling decisions when new task is added NUS.SOC.CS5248 OOI WEI TSANG

37. Computing Scheduling Graph • Input: A set of tasks with their reservations • Output: A scheduling graph if feasible NUS.SOC.CS5248 OOI WEI TSANG

38. Many Possible Solutions C A A B E B E F F D D C NUS.SOC.CS5248 OOI WEI TSANG

39. C A F B E F D NUS.SOC.CS5248 OOI WEI TSANG

40. Computing Scheduling Graph • Input: A set of tasks with their reservations • Output: A scheduling graph if feasible • Goals: (a) Minimize context switches (b) Distribute free time evenly NUS.SOC.CS5248 OOI WEI TSANG

41. Life is Tough.. NP-Hard NUS.SOC.CS5248 OOI WEI TSANG

42. Heuristic 10 10 10 10 10 10 10 NUS.SOC.CS5248 OOI WEI TSANG

43. 10 5 F 5 5 10 10 10 NUS.SOC.CS5248 OOI WEI TSANG

44. 6 1 F 1 B+E 1 6 6 6 NUS.SOC.CS5248 OOI WEI TSANG

45. C 4 1 F 1 B+E 1 1 1 A+D 1 NUS.SOC.CS5248 OOI WEI TSANG

46. B E C B E A D B E F B E A D NUS.SOC.CS5248 OOI WEI TSANG

47. Time Constraints

48. Time Constraint • “I need to run the following code, that takes 30ms, 100ms from now, and the deadline is (now+180ms).” NUS.SOC.CS5248 OOI WEI TSANG

49. Pseudocode can = begin_constraint(start_time, deadline, estimate) if can schedule then do work else adapt time_taken = end_constraint() NUS.SOC.CS5248 OOI WEI TSANG

50. Scheduling Constraints C A F B E F D NUS.SOC.CS5248 OOI WEI TSANG