1 Course Matters
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1
Course Matters
NUS.SOC.CS5248OOI WEI TSANG
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Paper Review
October 2003
Mon Tue Wed Thu Fri Sat Sun
17 18 19
20 21 22 23 24 25 26
Paper Reviews Due20% off for each late day
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Diwali/Deepavali
October 2003
Mon Tue Wed Thu Fri Sat Sun
17 18 19
20 21 22 23 24 25 26
No Class
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Guest Lecture
October 2003
Mon Tue Wed Thu Fri Sat Sun
17 18 19
20 21 22 23 24 25 26
CS6212 Guest Lecture“A/V Synchronization”SR1 4-6pm
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Books
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Project Grading
Proposal5%
Paper20%
Poster20%
Contribution20%
Methodology 35%
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Previously, on CS5248
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Cello
OS disk schedulerSupport multiple classesProtect classes from each otherWork conservingUse two-level scheduling
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CPU vs Disk SchedulingTask computation time
unpredictable
Task can be preemptive
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Problem
How can multimedia applications co-exists with normal applications?
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Same Old Idea
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Same Gang
P. Goyal, X. Guo, and H. M. Vin.
“A hierarchical CPU scheduler formultimedia operating systems.”
OSDI’96
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So Far
Best-Effort Real-Time
Scheduling
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How to Guarantee Services?
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Resource Reservation: CPU
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Resource Reservations
How to reserve?Overbook?Overuse?
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Example: Memory
How to reserve?malloc
Overbook? return NULL
Overuse? crash, throw exception
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Example: Memory
How to reserve?“I will need 128KB”
Overbook? “Sorry!”
Overuse? malloc returns NULL
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Example: CPU
How to reserve?Overbook?Overuse?
Memory is discrete. CPU time is continuous.
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How to Reserve?
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CPU Reservation
“I need C units of time, out of every T units.”
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Two Problems
How to determine C?take measurement and estimate
What if C is not constant?take the maximum
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Effects of T and C
0%10%20%30%40%50%60%70%80%90%
100%
0 10 20 30 40 50 60Reservation Period (ms)
% F
ram
es
Re
ndere
d
20% 15% 10%
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CPU Scheduling Algorithm
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Classic Real-Time Scheduler
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Rate Scheduling AlgorithmsRate MonotonicEarliest Deadline First
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Rate Monotonic
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EDF
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Classic Schedulability TheoremsRate Monotonic Scheduler
Earliest Deadline First2ln
i
i
T
C
2lni
i
T
C
1i
i
T
C
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Assumptions
programs are periodiccomputation time is constantzero context switch timeprograms are independent
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Why do we care about RM?Theoretically, RM has lower CPU
utilization (70%) butRM is more efficient than EDFCan support up to 80-90% CPU
utilization in practiceDon’t want to commit 100% CPU
anyway (for emergency)
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Rialto Scheduler
From MS Research
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Overview
Given a set of task, pre-compute a scheduling graph
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Task A B C D E F
Amount 4 3 2 1 1 5
Period 20 10 40 20 10 40
EB CA
EB FD
EB A
EB D
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Task A B C D E F
Amount 4 3 2 1 1 5
Period 20 10 40 20 10 40
C
F
A
D
EB
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Advantages
Only need to make new scheduling decisions when new task is added
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Computing Scheduling GraphInput: A set of tasks with their
reservationsOutput: A scheduling graph if
feasible
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Many Possible Solutions
C
F
A
D
EBF
C
A
D
EB
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Task A B C D E F
Amount 4 3 2 1 1 5
Period 20 10 40 20 10 40
C
F
F
A
D
EB
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Computing Scheduling GraphInput: A set of tasks with their
reservationsOutput: A scheduling graph if
feasibleGoals: (a) Minimize context
switches (b) Distribute free time evenly
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Life is Tough..
NP-Hard
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Heuristic
10
10
10
10
10
10
10
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10
5
10
10
5
10
5
F
Task A B C D E F
Amount 4 3 2 1 1 5
Period 20 10 40 20 10 40
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6
1
6
6
1
6
1
F
B+E
Task A B C D E F
Amount 4 3 2 1 1 5
Period 20 10 40 20 10 40
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4
1
1
1
1
1
1
F
B+E
A+D
C
Task A B C D E F
Amount 4 3 2 1 1 5
Period 20 10 40 20 10 40
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Task A B C D E F
Amount 4 3 2 1 1 5
Period 20 10 40 20 10 40
EB C
EB DA
EB F
EB A D
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Time Constraints
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Time Constraint
“I need to run the following code, that takes 30ms, 100ms from now, and the deadline is (now+180ms).”
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Pseudocode
can = begin_constraint(start_time, deadline, estimate)
if can schedule thendo work
elseadapt
time_taken = end_constraint()
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Scheduling Constraints
C
F
F
A
D
EB
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Scheduling Constraints
C
F
F
A
D
EB
C1, C2, C5
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Advantages of Scheduling GraphOnly need to make new
scheduling decisions when new task is added
Feasibility of time constraint can be predicted accurately
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Peaceful Coexistence
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Running Unreserved Task
C
F
F
A
D
EB
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Media Player on Rialto/NT
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Look inside NT SchedulerScheduling unit : ThreadPriority level: 1-15, 16-31
rt 24 high 13 normal 8 idle 4
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Priority Boosting
Example:Priority +6 after awaken by
keyboard input
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Anti-Starvation
If hasn’t run for 3 secondsBoost priority to 14
Avoid “Priority Inversion”
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Mars Pathfinder
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Rialto/NT
NT Scheduler
RialtoC
F
F
A
D
EB
Boost Priorityto 30
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Win Media Player 6.4
Period Priority Thread
10 24 Kernel Mixer
45 8 GUI
100 15 Timer
100 9 MP3 Decoder
500 8 Unknown
2000 8 Disk Reader
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Experiment 1
WMP running alone
Period Priority Thread
10 24 Kernel Mixer
45 8 GUI
100 15 Timer
100 9 MP3 Decoder
500 8 Unknown
2000 8 Disk Reader
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Experiment 2
WMP running with priority 8 competitor
Period Priority Thread
10 24 Kernel Mixer
45 8 GUI
100 15 Timer
100 9 MP3 Decoder
500 8 Unknown
2000 8 Disk Reader
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Experiment 3
WMP running with priority 10 competitor
Period Priority Thread
10 24 Kernel Mixer
45 8 GUI
100 15 Timer
100 9 MP3 Decoder
500 8 Unknown
2000 8 Disk Reader
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Experiment 5
WMP running with priority 10 competitor
Period Priority Reservation Thread
10 24 Kernel Mixer
45 8 GUI
100 15 Timer
100 9 40/1024 MP3 Decoder
500 8 Unknown
2000 8 Disk Reader
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Experiment 6
WMP running with priority 10 competitor
Period Priority Reservation Thread
10 24 1/16 Kernel Mixer
45 8 GUI
100 15 Timer
100 9 40/1024 MP3 Decoder
500 8 Unknown
2000 8 Disk Reader
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Experiment 7
WMP running with priority 10 competitor
Period Priority Reservation Thread
10 24 Kernel Mixer
45 8 GUI
100 15 Timer
100 9 20/512 MP3 Decoder
500 8 Unknown
2000 8 Disk Reader
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Summary
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CPU Scheduling
With guaranteepercentage of CPU timetask with deadline
AlgorithmsRate-monotonicEDFRialto
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CS5248 Summary
Network
Encoder
Sender
Middlebox
Receiver
Decoder
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Last Two Lectures
October/November 2003
Mon Tue Wed Thu Fri Sat Sun
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3 4 5 6 7 8 9
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Last Two Lectures
Papers from recent conferences and journals.
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