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Issues about Scheduling for Dependent Multimedia Tasks
電機所控制組 R92921065 馮天俊 R92921066 戴兆弘
Adviser :陳少傑 老師Date : 2004/06/01
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Outline
Motivation Introduction to Multimedia Task Allocation & Scheduling Issue Scheduling Algorithms Conclusion & Future Work References
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Outline
Motivation Introduction to Multimedia Task Allocation & Scheduling Issue Scheduling Algorithms Conclusion & Future Work References
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Motivation
A popular issue along with the progressive
network technology Get the inspiration from the talk introduced by
Professor Huang three weeks ago
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Outline
Motivation
Introduction to Multimedia Task Allocation & Scheduling Issue Scheduling Algorithms Conclusion & Future Work References
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What is Multimedia ? Different kinds of data Combination of two or more continuous
media (audio and video)
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Characteristics of Multimedia [3: Barroso et al. 1998]
The quality of information depends on the
time it is presented to the user Soft real-time task Produced and retrieved by periodic
processes
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Scheduling Problem Addressing [3: Barroso et al. 199
8]
A labeled, directed, acyclic graph
node : a task link : a precedence betw
een two tasks Three types of tasks
• Multimedia Task Graph (MTG) model
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Outline
Motivation Introduction to Multimedia
Task Allocation & Scheduling Issue Scheduling Algorithms Conclusion & Future Work References
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Task Allocation & Scheduling Issue
Task allocation : Task dependence Level dependence
Scheduling issue : Fully Synchronized Pipelining (FSP) Approach Partially Synchronized Pipelining (PSP) Approach
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Task Allocation ---Task Dependence [2: Hwang 1994]
The scheduling algorithm can be implemented in the following steps : Step 1 Initiate the ready task set Step 2 Select and schedule a task in the ready task set Step 3 If there are any tasks whose precedence constraints are satisfied due to the execution of Step 2, add it to the ready task set Step 4 Go to Step 2 until all tasks are scheduled
1st round : T1 T2 T3 < if T1 is scheduled > 2nd round : T4 T2 T3 < if T3 is scheduled > 3rd round : T4 T7 T8 …
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Task Allocation ---Level Dependence [2: Hwang 1994]
The level number of task Ti can be defined as :
where length(Ti)= the longest path among all the paths traversed from the starting nodes
to the Ti L=1 : T1 T2 T3 L=2 : T4 T5 T6 T7 T8 L=3 : T9 T10 T11 L=4 : T12 T13
otherwiseTilength
taskstartingaisTiwheniL
),(
,1)(
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Scheduling Issue---FSP [2: Hwang 1994]
All tasks with same period are scheduled into
the same slot of processors
Advantage Simplicity
Disadvantage Longer response time A task system with tight deadlines may become unschedula
ble
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Scheduling Issue---PSP [2: Hwang 1994]
Only the start time of periodic starting tasks
is synchronized
Advantage Overlap on task’s executions Produce results with shorter response time
Disadvantage More complicated Require longer scheduling time
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Outline
Motivation Introduction to Multimedia Task Allocation & Scheduling Issue
Scheduling Algorithms Conclusion & Future Work References
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The Branch and bound Algorithm [2]
It is divided two parts Allocation procedure
The search tree is extended by considering the allocation of T1 to every processor ,denoted by ,
Ex. Tasks=3, Processors=2
jP
jPT 1mj ~1
T1
T2
T3
T1
T2
T3
P1 P2
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The Branch and bound Algorithm (cont’d) It is divided two parts
Scheduling procedure
Branch P1 : T1T3 P2 : T2
T1
T2
T3
T1
T2
T3
P1
P2T1
T2
T3
T1
T2
T3
P1 choose T1P1 choose T3
P2 choose T2
T1
T2
T3
T1
T2
T3
T1
T2
T3
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The Dependent Earliest-Deadline-First Algorithm A variation of traditional earliest-deadline-first
policy
Earliest-deadline-first (EDF) algorithm : [5: Liu & Layland 1973] [6: Krishna & Shin 1997]
Higher priority for earlier deadline Dynamic priority scheduling algorithm Schedulable iff
n
i i
i
P
eU
1
1
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The Dependent Earliest-Deadline-First Algorithm (cont’d) Using the task dependence approach Only the tasks in LR can participate in the
scheduling selection competition LR : A list of ready tasks
The winner is the one with earliest deadline Schedule the tasks with EDF
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The Level Oriented Algorithm [2]
The tasks are scheduled level by level The sorting makes the tasks with the smallest
period go first The tasks in the same level are allocated in
different processors
Advantage Can reduce execution time by parallel
processing
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Comparison of above three algorithms
Here, consider two criteria : The number of processors The execution time of the algorithms
Conclusion One compromise can be made with weighting for each Criterion Weighting can be defined case by case
B & B Dependent EDF Level Oriented
# of processors Fewest Medium Most
Execution time Longest Medium Shortest
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Outline
Motivation Introduction to Multimedia Task Allocation & Scheduling Issue Scheduling Algorithms
Conclusion & Future Work References
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Conclusion & Future Work
Conclusion A brief study about the problem of dependent
real-time multimedia task scheduling A set of scheduling techniques for multimedia
tasks on distributed system are investigated
Future Work Add more hardware consideration in our
project
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Outline
Motivation Introduction to Multimedia Task Allocation & Scheduling Issue Scheduling Algorithms Conclusion & Future Work
References
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References
[1] Hsing Mei Hwang, ”Scheduling Dependent Real-Time Multimedia Tasks on Distributed Systems,” The 19th Annual International Computer Software & Application Conference, Dallas, USA,1995, pp.306-311. [2] Hsing Mei Hwang, ”Scheduling Multimedia Tasks on Distributed Systems Based on MTG Model,” Technical Report 94-M001, CSIE Department, Fu Jen Catholic University, Jan 1994. [3] Andre Barroso, Andreas Manoli, Michail Petropoulos, “Issues in Multimedia Task Scheduling,“ Nov.21, 1998[4] John Regehr, Michael B. Jones, John A. Stankovic, “Operating System Support for Multimedia: The Programming Model Matters,” Technical Report MSR-TR-2000-89, Microsoft Corporation, Sep. 2000[5] C.L. Liu, J.W. Layland, "Scheduling Algorithms for Multiprogramming in a Hard-real-time Environment," Journal of ACM, Vol. 20, No. 1, pp. 46-61, Jan. 1973 [6] Krishna & Shin, “Real-Time Systems,” 1997
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