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Unformatted text preview: Assignment 4 , Mechtron/Sfwr Eng 4aa4
1) Explain the diﬀerences between RM, DM, EDF scheduling. Which of
these follow a dynamic priority policy?
Ans: All are priority based algorithms. In RM priority of a task is
ﬁxed based on its period and it remains ﬁxed during the life time of
the system, whereas in DM the priority is ﬁxed based on the deadline
of a task. A task that has the shortest period/relative deadline has
the highest priority. In EDF priorities are calculated based on absolute deadlines of diﬀerent tasks at a given time. The task that has
the earliest absolute deadline gets the highest priority. EDF is a dynamic priority algorithm in which priorites of tasks keep on changing
2) Consider the following 5 independent tasks with the speciﬁed periods:
A(30, 5), B (4, 1), C (10, 2), D (8, 1), E (20, 1)
a) Conﬁrm that the task set is EDF schedulable.
As the periods of the tasks are equal to their deadlines, to be EDF
= 0.79166 ≤ 1
30 4 10 8 20
Therefore the task set is EDF schedulable.
U= b) Draw a graph showing how an EDF (Earliest Deadline First) policy would attempt to schedule the tasks for t = 0 to 40.  1 Figure 1: 2 3) Consider an overloaded system consisting of the following task set:
T1 (2, 1), T2 (5, 3)
a) Graphically show a schedule based on RM algorithm and another
based on EDF algorithm for 15 time units.[4 + 4]
b) Comparing the two schedules, what can be concluded about predictability of the two algorithms?  Figure 2: EDF and RM schedules
Comparing the two schedules it is obvious that RM is more pridictable
as the same lower priority task misses the dealines. 3 ...
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This note was uploaded on 12/13/2011 for the course SOFTWARE E SFWR ENG 4 taught by Professor Bokhari during the Fall '11 term at McMaster University.
- Fall '11