MADE EASY TEST SERIES

Question

Consider the following preemptive priority scheduling algorithms based on dynamically changing priorities. Large priority numbers imply higher priority. When the process is waiting for the CPU in ready queue, its priority changes at a rate ‘α’; when its running, its priority changes at a rate ‘β’. All processes are given a priority, when they enter the ready queue. Which one of the CPU scheduling algorithm results from α > β > 0 ?

• Round Robin Algorithm
• Shortest Job First Algorithm
• First Come First Serve Algorithm
• Last-In-First-Out

Comments

i think round robin should be answer.

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I also answered same but made easy says option D is the correct answer. Exact solution provided by Made easy is: "New process in this algorithm will always ran immediately and older process will sit in the ready queue until the most recent process finishes. This is essentially last in first out algorithm." Please guide.

How LIFO can be used for process scheduling? Could you please give me an example. Thank you.

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it will be LIFO if $\alpha<\beta<0$

Answer 1

i think round robin should be answer.

if u consider a case where there are 3 processes and all have same priority and let that priority be x

Let alpha be 'a' and beta be 'b'

assume P₁ will be executed first and in case of equal priority lower index process will be executed first

Process	t=0	t=1	t=2	t=3	t=4	t=5
P1	x	x+b	x+b+a	x+b+a+a	x+b+a+a+b	x+b+a+a+b+a
P2	x	x+a	x+a+b	x+a+b+a	x+b+a+a+a	x+b+a+a+a+b
P3	x	x+a	x+a+a	x+a+a+b	x+a+a+b+a	x+a+a+b+a+a

Now from above table I have bold the priority which is higher at a particular time

From the above table we also found that the processes are getting executed in RR fashion

Also if we go optionwise C) and D) will never be the answer becoz they are not preemptive scheduling algo

Also when a process is getting executed it's running time gonna decrease. So we should keep executing that process. But according to questing we are increasing the priority of running process by 'b' and ready process by 'a'. Also a>b, so after some time priority of one of the ready process will become greater than running process, as a result even though the running process has shorter remaining time it will get preempted