Page 136 - DCAP608_REAL TIME SYSTEMS

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

 When a group of tasks share a common resource a scheduling policy is necessary to Notes
arbitrate access to the shared resource.

 During a process of interactive system design and rapid system prototyping, the system
designer typically makes a large number of calls to a feasibility-analysis algorithm, since
proposed designs are modified according to the feedback offered by the feasibility-analysis
algorithm

13.4 Keywords

Schedulability Test: A test for the purpose of validating that the given application system can
indeed meet all its hard deadlines when scheduled according to the chosen scheduling algorithm
is called a Schedulability test.

Scheduling Points: The scheduling points of a scheduler are the points on the time line at which
the scheduler makes decisions regarding which task is to be run next.
Time Demand Analysis: A schedulability test for fixed-priority systems is the time demand
analysis.
Utilization: The processor utilization of a task is the average time for which it executes per unit
time interval.

Valid Schedule: It is one where at most one task is assigned to a processor at a time, no task is
scheduled before its arrival time, and the precedence and resource constraints of all tasks are
satisfied.

13.5 Review Questions

1. Explain the term Schedulability test.
2. Explain the concept of Schedulability Test for Fixed-Priority Tasks with Short Response
Times.
3. What is time demand analysis?
4. Elucidate the Role of critical instants in fixed priority tasks.
5. Discuss the concept of Optimality of RM and DM Algorithm.

Answers: Self Assessment

1. Fixed priority 2. deadline
3. Algorithm 4. True
5. False 6. Schedulability
7. arbitrate 8. worst-case response

9. Critical applications 10. Fixed Priorities(FP)

13.6 Further Readings

Books Alan Burns and Andy Wellings (2001). Real-Time Systems and Programming
Languages, Addison Wesley.

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