1 Course Matters

NUS.SOC.CS5248 OOI WEI TSANG 2 Paper Review October 2003 MonTueWedThuFriSatSun Paper Reviews Due 20% off for each late day

NUS.SOC.CS5248 OOI WEI TSANG 3 Diwali/Deepavali October 2003 MonTueWedThuFriSatSun No Class

NUS.SOC.CS5248 OOI WEI TSANG 4 Guest Lecture October 2003 MonTueWedThuFriSatSun 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

7 Previously, on CS5248

NUS.SOC.CS5248 OOI WEI TSANG 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?

15 Resource Reservation: CPU

NUS.SOC.CS5248 OOI WEI TSANG 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? Memory is discrete. CPU time is continuous.

20 How to Reserve?

NUS.SOC.CS5248 OOI WEI TSANG 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

24 CPU Scheduling Algorithm

25 Classic Real-Time Scheduler

NUS.SOC.CS5248 OOI WEI TSANG 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)

32 Rialto Scheduler From MS Research

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

NUS.SOC.CS5248 OOI WEI TSANG 34 TaskABCDEF Amount Period EBCA EBFD EBA EBD

NUS.SOC.CS5248 OOI WEI TSANG 35 TaskABCDEF Amount Period C F A D EB

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 F A D EB F C A D EB

NUS.SOC.CS5248 OOI WEI TSANG 39 TaskABCDEF Amount Period C F F A D EB

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

NUS.SOC.CS5248 OOI WEI TSANG F TaskABCDEF Amount Period

NUS.SOC.CS5248 OOI WEI TSANG F B+E TaskABCDEF Amount Period

NUS.SOC.CS5248 OOI WEI TSANG F B+E A+D C TaskABCDEF Amount Period

NUS.SOC.CS5248 OOI WEI TSANG 46 TaskABCDEF Amount Period EBC EBDA EBF EBAD

47 Time Constraints

NUS.SOC.CS5248 OOI WEI TSANG 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 F F A D EB

NUS.SOC.CS5248 OOI WEI TSANG 51 Scheduling Constraints C F F A D EB C1, C2, C5

NUS.SOC.CS5248 OOI WEI TSANG 52 Advantages of Scheduling Graph Only need to make new scheduling decisions when new task is added Feasibility of time constraint can be predicted accurately

53 Peaceful Coexistence

NUS.SOC.CS5248 OOI WEI TSANG 54 Running Unreserved Task C F F A D EB

55 Media Player on Rialto/NT

NUS.SOC.CS5248 OOI WEI TSANG 56 Look inside NT Scheduler Scheduling unit : Thread Priority level: 1-15, rt 24 high 13 normal 8 idle 4

NUS.SOC.CS5248 OOI WEI TSANG 57 Priority Boosting Example: Priority +6 after awaken by keyboard input

NUS.SOC.CS5248 OOI WEI TSANG 58 Anti-Starvation If hasn’t run for 3 seconds Boost priority to 14 Avoid “Priority Inversion”

NUS.SOC.CS5248 OOI WEI TSANG 59 Mars Pathfinder

NUS.SOC.CS5248 OOI WEI TSANG 60 Rialto/NT NT Scheduler Rialto C F F A D EB Boost Priority to 30

NUS.SOC.CS5248 OOI WEI TSANG 61 Win Media Player 6.4 PeriodPriorityThread 1024Kernel Mixer 458GUI 10015Timer 1009MP3 Decoder 5008Unknown 20008Disk Reader

NUS.SOC.CS5248 OOI WEI TSANG 62 Experiment 1 WMP running alone PeriodPriorityThread 1024Kernel Mixer 458GUI 10015Timer 1009MP3 Decoder 5008Unknown 20008Disk Reader

NUS.SOC.CS5248 OOI WEI TSANG 63 Experiment 2 WMP running with priority 8 competitor PeriodPriorityThread 1024Kernel Mixer 458GUI 10015Timer 1009MP3 Decoder 5008Unknown 20008Disk Reader

NUS.SOC.CS5248 OOI WEI TSANG 64 Experiment 3 WMP running with priority 10 competitor PeriodPriorityThread 1024Kernel Mixer 458GUI 10015Timer 1009MP3 Decoder 5008Unknown 20008Disk Reader

NUS.SOC.CS5248 OOI WEI TSANG 65 Experiment 5 WMP running with priority 10 competitor PeriodPriorityReservationThread 1024Kernel Mixer 458GUI 10015Timer /1024MP3 Decoder 5008Unknown 20008Disk Reader

NUS.SOC.CS5248 OOI WEI TSANG 66 Experiment 6 WMP running with priority 10 competitor PeriodPriorityReservationThread 10241/16Kernel Mixer 458GUI 10015Timer /1024MP3 Decoder 5008Unknown 20008Disk Reader

NUS.SOC.CS5248 OOI WEI TSANG 67 Experiment 7 WMP running with priority 10 competitor PeriodPriorityReservationThread 1024Kernel Mixer 458GUI 10015Timer /512MP3 Decoder 5008Unknown 20008Disk Reader

68 Summary

NUS.SOC.CS5248 OOI WEI TSANG 69 CPU Scheduling With guarantee percentage of CPU time task with deadline Algorithms Rate-monotonic EDF Rialto

NUS.SOC.CS5248 OOI WEI TSANG 70 CS5248 Summary Network Encoder Sender Middlebox Receiver Decoder

NUS.SOC.CS5248 OOI WEI TSANG 71 Last Two Lectures October/November 2003 MonTueWedThuFriSatSun

NUS.SOC.CS5248 OOI WEI TSANG 72 Last Two Lectures Papers from recent conferences and journals.