Page 128 - DCAP608_REAL TIME SYSTEMS

Unit 12: Priority-driven Scheduling of Periodic Tasks

12.5 Keywords Notes

Dynamic-priority Algorithm: A dynamic-priority algorithm assigns different priorities to the
individual jobs in each task.

EDF: Earliest-deadline-first scheduling, at every scheduling point the task having the shortest
deadline is taken up for scheduling.
Fixed-priority Algorithm: A fixed-priority algorithm assigns the same priority to all the jobs in
each task.
Rate Monotonic Algorithm: It is a static priority algorithm and is extensively used in practical
applications.
Scheduling Points: These are the points on time line at which the scheduler makes decisions
regarding which task is to be run next.
12.6 Review Questions

1. What is Priority-driven scheduling?
2. Explain the static assumptions of Priority-driven scheduling.
3. Define and Differentiate between Fixed-priority and Dynamic-priority.
4. Discuss the concept of schedulable utilization UALG of a scheduling algorithm with
example.
5. What do you mean by Rate Monotonic and Deadline Monotonic Algorithms?
6. Discuss types of EDF assigned tasks with the help of figures and illustration.

Answers: Self Assessment

1. Scheduler 2. static system
3. dynamic 4. multiprocessor
5. distributed systems 6. False
7. False 8. True

9. True 10. True
11. periodic tasks 12. LST rule

12.7 Further Readings

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

C. M. Krishna and K. G. Shin (1997). Real-Time Systems. McGraw-Hill International
Editions.
O’Reilly Editor (1995). Programming for the real world.

Ben-Ari, M. (1990). “Principles of Concurrent and Distributed Programming”, Prentice
Hall).

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