Question

Answer the following question: A Multi Level Feedback (MLF) algorithm uses 5 priority levels. All levels are using Round Robin (RR) Scheduling algorithm with Quantum: 1 ms, 2 ms, 4 ms, 8 ms, 16 ms respectively. Processes start at highest priority (Q=1) and is down graded to the lower priority if it didn't finish within 1 quantum. The following processes are to be scheduled: Arrival Io Wait 0 3 Process P1 P2 P3 CPU Burst 2 4 15 4 1 2 10 wait time is the time it takes for the process to become ready again. Show the CPU allocation every 1 ms till process p3 terminates after completing its 15 ms burst. Assume the scheduling algorithm is non-preempt-able, i.e. when a quantum starts it has to finish. The following is how the sequence starts, copy and complete the sequence: 123,.... (format: don't leave spaces or use any comma or separator)

Answer 1

In starting only P1 will be available in the ready queue and then at time 1 and 2 process P2 and P3 will arrive

Execution in highest priority level (Order in ready queue: P1P2P3)

0 $\rightarrow$ 1ms ----P1 // P1 down graded to the 1st lower priority level ready queue

1 $\rightarrow$ 2ms ----P2 // P2 down graded to the 1st lower priority level ready queue

2 $\rightarrow$ 3ms ----P3 // P3 down graded to the 1st lower priority level ready queue

Execution in 1st lower priority level (Order in ready queue: P1P2P3)

3 $\rightarrow$ 4ms ----P1 // P1 CPU time is completed. Now CPU will move to I/O state

4 $\rightarrow$ 6ms ----P2 // P2 down graded to the 2nd lower priority level ready queue

6 $\rightarrow$ 8ms ----P3 // P3 down graded to the 2nd lower priority level ready queue

At 7ms P1 will complete its I/O operation and and move to 2nd lower priority level ready queue

Execution in 2nd lower priority level (Order in ready queue: P2P1P3)

8 $\rightarrow$ 9ms ----P2 // P2 CPU time is completed. Now CPU will move to I/O state

9 $\rightarrow$ 11ms ----P1 // P1 CPU time is completed. Now CPU will move to I/O state

11 $\rightarrow$ 15ms ----P3 // P3 down graded to the 3rd lower priority level ready queue

At 13ms P2 will complete its I/O operation and and move to 3rd lower priority level ready queue while at 14ms P1 will complete its I/O operation and and move to 3rd lower priority level ready queue

Execution in 3rd lower priority level (Order in ready queue: P2P1P3)

15 $\rightarrow$ 19ms ----P2 // P2 CPU time is completed. Now CPU will move to I/O state

19 $\rightarrow$ 21ms ----P1 // P1 CPU time is completed. Now CPU will move to I/O state

21 $\rightarrow$ 29ms ----P3 // P3 will execute at this time.

Sequence of execution for every 1 ms: 12312233211333322221133333333

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