Page 130 - DCAP608_REAL TIME SYSTEMS

Gurwinder Kaur, Lovely Professional University Unit 13: Working of Priority-driven Scheduling of Periodic Tasks

Unit 13: Working of Priority-driven Notes
Scheduling of Periodic Tasks

CONTENTS
Objectives
Introduction

13.1 Optimality of RM and DM Algorithm
13.2 Schedulability Test
13.2 .1 A Schedulability Test for Fixed-Priority Tasks with Short Response Times
13.2 .2 A Schedulability Test for Fixed-Priority Tasks with Arbitrary
Response Times
13.3 Summary
13.4 Keywords

13.5 Review Questions
13.6 Further Readings

Objectives

After studying this unit, you will be able to:

 Describe Optimality of RM and DM Algorithm
 Enumerate A Schedulability Test for Fixed-Priority Tasks with Short Response Times
 Explain A Schedulability Test for Fixed-Priority Tasks with Arbitrary Response Times

Introduction

Utilization-based conditions are deduced for finding out if a periodic task system fulfils each
deadline when scheduled by means of the EDF scheduling algorithm upon a given multiprocessor
platform. In the context of the uniprocessor, when exactly one shared processor is obtainable
upon which to perform every job generated by each task in the system, it is known that the EDF
(earliest deadline first) scheduling algorithm, which executes at every instant in time the presently
active job is a best scheduling algorithm. That is, if a system can be arranged such that every
deadline can be fulfilled, this system is fulfilled by earliest deadline first. Algorithm will schedule
in order to fulfil every deadline. In this unit, we will discuss the Working of Priority Driven
Scheduling of Periodic Tasks.

13.1 Optimality of RM and DM Algorithm

Fixed priority algorithms can be optimal in restricted systems. A system of periodic tasks is
simply periodic if the period of each task is an integer multiple of the period of the other tasks:
p = n p
k i
where p < p (p has higher priority than p ) and n is a positive integer; for all T and T .
i k i k i k
We discussed a flight control system, the shortest period was 1/180 seconds and the other two
periods were 2*1/180 and 6*1/180.

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