Scheduling exercises

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Let's practice the algorithms:

Given those processes:

Process	Arrival time	Burst time (ms)
P1	1	4
P2	0	3
P3	3	5
P4	2	8
P5	3	1
P6	2	7
P7	4	5

Exercise 1: Apply Round Robin with q = 3 and write the Gantt chart

💡Answer

A solution is to add them by arrival time. P1, then P4, P6, and P3, P5.

Queue time 0 :

Process	Time left
P2	3

Queue time 3:

Process	Time left
P1	4
P4	8
P6	7
P3	5
P5	1

Queue time 6:

Process	Time left
P4	8
P6	7
P3	5
P5	1
P7	5
P1	1

(we've added P7 first, and then P1)
...

Exercise 2: Calculate average wait time for the Round Robin with q = 3

💡Answer

P1 : 2 + 13 = 51 wait time
P2: 0
P3: 12 - 3 + 26 - 15 = 18
P4: 4 + 11 + 7 = 32
P5: 12
P6: 7 + 11 + 6 = 24
P7: 12 + 9 = 21

Avg wait time: 16

Exercise 3: write the gantt chart for SJF preemptive

💡Answer

On the exam, you can split in multiple boxes from 1 to 1 time unit.
e.g. P2 0 1, P2 1 2, P2 1 3... (to illustrate that you verify for other processes) (but specify you don't do a context switch there)

Exercise 4: Average time for SJF preemptive.

Given this table with processes:

Process	Arrival time	Burst time (ms)	Priority
P1	0	4	3
P2	2	3	5
P3	4	5	1
P4	2	8	2
P5	3	1	4
P6	6	7	5

Exercise 5: Do the Gantt chart for SJF preemptive and non-preemptive

Hint: When you are running a process, if another comes with a bigger priority or same one but smaller burst time, context switch. After you end the process, take the smallest job first.

💡Answer