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Suppose the following jobs are to be executed in a uniprocessor system.

Multilevel Feedback Queue(MLQ) is used with queues numbered 1-10, quantum = 2i, where i is thequeue level number and processes are initially placed in the first queue (i.e., level 1). In this schedulingpolicy, each process executes at a particular level for one quantum and then moves down a level; processesnever move up a level. The average process turnaround time, the normalized turnaround time for process2, and the processor efficiency using MLQ is,

1.

11.4, 2, 83.3%

2. 

18, 4.25, 71.4%

3.

18.6, 3.375, 71.4%

4.

11.6, 3.75, 80.6%

 

Need good explanation :( (answer given is b.)

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In multilevel queue scheduling , if one level time quantum exits, it goes to next lower level 

ML Queue Scheduling uses RR scheduling

Here it is given time quantum of 1st level queue is 2 ms

2nd level of queue is 4 ms

and 3rd level queue is 8 ms

Now, solve accordingly

$P_{1}$ $P_{2}$ $P_{3}$ $P_{1}$ $P_{2}$ $P_{4}$ $P_{5}$ $P_{4}$ $P_{5}$ $P_{2}$

$0.$          $2$          $4$.         $6$.            $8$.         $12$        $14$.        $16$.        $20$.       $23$.        $25$

$\underbrace{.{\color{Magenta}{1st- level-queue } } }$$\underbrace{.{\color{blue}{2nd-- level } } }$$\underbrace{.{\color{Magenta}{1st-- level } } }$$\underbrace{.{\color{blue}{2nd-level } } }$$\underbrace{.{\color{red}{3rd- level } } }$

Now, Throughput for all processes $\frac{8+24+3+10+11}{5}=11.2 ms$

Efficiency $\frac{25}{\left ( 2\times 5 \right )+\left ( 4\times 4 \right )+8}\times 100=73.5 ms$

https://www.youtube.com/watch?v=cApdURNWJPc

https://www.cs.uic.edu/~jbell/CourseNotes/OperatingSystems/5_CPU_Scheduling.html

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