Problem-
Consider the set of 5 processes whose arrival time and burst time are given below-
Process Id Arrival time Burst time
P0 0 3
P1 2 6
P2 4 4
P3 6 5
P4 8 2
If the CPU scheduling policy is Highest Response Ratio Next, calculate the average
waiting time and average turn around time.
Solution-
Step-01:
At t = 0, only the process P0 is available in the ready queue.
So, process P0 executes till its completion.
Step-02:
At t = 3, only the process P1 is available in the ready queue.
So, process P1 executes till its completion.
Step-03:
At t = 9, the processes P2, P3 and P4 are available in the ready queue.
The process having the highest response ratio will be executed next.
The response ratio are-
Response Ratio for process P2 = [(9-4) + 4] / 4 = 9 / 4 = 2.25
Response Ratio for process P3 = [(9-6) + 5] / 5 = 8 / 5 = 1.6
Response Ratio for process P4 = [(9-8) + 2] / 2 = 3 / 2 = 1.5
Since process P2 has the highest response ratio, so process P2 executes till completion.
Step-04:
At t = 13, the processes P3 and P4 are available in the ready queue.
The process having the highest response ratio will be executed next.
The response ratio are calculated as-
Response Ratio for process P3 = [(13-6) + 5] / 5 = 12 / 5 = 2.4
Response Ratio for process P4 = [(13-8) + 2] / 2 = 7 / 2 = 3.5
Since process P4 has the highest response ratio, so process P4 executes till completion.
Step-05:
At t = 15, only the process P3 is available in the ready queue.
So, process P3 executes till its completion.
Now, we know-
Turn Around time = Exit time – Arrival time
Waiting time = Turn Around time – Burst time
Also read- Various Times of Process
Process Id Exit time Turn Around time Waiting time
P0 3 3–0=3 3–3=0
P1 9 9–2=7 7–6=1
P2 13 13 – 4 = 9 9–4=5
P3 20 20 – 6 = 14 14 – 5 = 9
P4 15 15 – 8 = 7 7–2=5
Now,
Average Turn Around time = (3 + 7 + 9 + 14 + 7) / 5 = 40 / 5 = 8 units
Average waiting time = (0 + 1 + 5 + 9 + 5) / 5 = 20 / 5 = 4 units
