Question $4-$ Process Scheduling $(40$ points$)$

$($This question is related to ILO$22a-$ "discuss the mechanisms and policies in efficiently sharing of CPU

resources" and ILO$3-$ "analyze and evaluate the algorithm and explain the performance issues".$)$

Consider there are seven processes running on a single$-$core processor machine. The following

table shows the arrival times and CPU burst times of the seven processes. Assume new processes

always be inserted to the ready queue just before the arrival time, e$.$g$.,$ at $t=7,B$ has been added to

the end of the ready queue.

Suppose a system uses Round Robin $($RR$)$ scheduling policy with a time quantum of $4$ time

units, and the context switching time is $1$ time unit.

a$.$ Draw the Gantt $($timeline$)$ diagram illustrating the execution of these processes under this

RR policy.

b$.$ What is the average turnaround time for the processes?

c$.$ What is the average waiting time for the processes?

d$.$ What is the average response time for the processes?

Consider another system using a variant of the Multilevel Feedback Queues $($MLFQ$)$

scheduling policy. This MLFQ system adopts the following set of rules:

It has $3$ priority levels with level $3$ as the highest priority and level $1$ is the lowest.

For level $3,$ its time quantum is set to $4$ time units; for level $2,$ it is set to $8$ time units; for

level $1,$ it is set to $12$ time units. Furthermore, assume the context switching time is $1$ time

unit.

Once a process uses up its time quantum at a given level, its priority is reduced $($i$.$e$.,$ it

moves down one queue$).$

Once a process is scheduled to be executed by the processor, it will only be switched out

by the scheduler if its time quantum has reached, i$.$e$.,$ it will not be preempted by the

arrival of higher priority processes.

a$.$ Draw the Gantt diagram illustrating the execution of those processes under this MLFQ

policy.

b$.$ What is the average turnaround time for the processes?

c$.$ What is the average waiting time for the processes?

d$.$ What is the average response time for the processes?