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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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