Read the following and answer the questions that follow. Consider the following set of processes with the arrival time and length of CPU Burst time given in milli-seconds (ms):Process Arrival Time Burst Time P1 0 5 P2 2 3 P3 2 2 P4 5 3 P5 6 1
Calculate the average response time for these processes with nonpreemptive priority Scheduling algorithm? Priority of the process are as follows and consider that all the processes came at zero (0) time. (Note low numbers represent high priority).Process Burst Time Priority P1 5 3 P2 3 1 P3 2 5 P4 3 4 P5 1 2
5.6 ms
Response time is the time from a process's arrival until it first gets the CPU. In non-preemptive priority scheduling the highest-priority ready process (here the smallest number) runs to completion before the next one is chosen.
Step 1 — All five processes are ready at t = 0, so the order is by priority: P2 (1), P5 (2), P1 (3), P4 (4), P3 (5).
Step 2 — Build the schedule:
| Process | Priority | Burst | Start | Finish | Response |
|---|---|---|---|---|---|
| P2 | 1 | 3 | 0 | 3 | 0 |
| P5 | 2 | 1 | 3 | 4 | 3 |
| P1 | 3 | 5 | 4 | 9 | 4 |
| P4 | 4 | 3 | 9 | 12 | 9 |
| P3 | 5 | 2 | 12 | 14 | 12 |
Step 3 — \(\text{Average response time} = \dfrac{0+3+4+9+12}{5} = \dfrac{28}{5} = 5.6\ \text{ms}\).
Averaging the finish times would give 42/5 = 8.4 ms and the order by burst time would give smaller values, so 5.2 ms, 4.7 ms and 3.8 ms do not follow from the priority order with arrival at time 0.
5.6 ms option is correct.
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Important Questions from CPU Scheduling
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- $M_2$ uses priority of execution for the processes as, $P_2 > P_3 > P_4 > P_1$, i.e., $P_2$ and $P_1$ have highest and lowest priorities, respectively.
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