Arrival Time: Time at which the process arrives in the ready queue.
Waiting Time(W.T): Time Difference between turn around time and burst time. Waiting Time = Turn Around Time - Burst Time
Burst Time: Time required by a process for CPU execution.
Completion Time: Time at which process completes its execution.
Turn Around Time: Time Difference between completion time and arrival time.
Turn Around Time = Completion Time - Arrival Time
Q3. What are the scheduling techniques used by Multilevel Feedback Queue Scheduling Algorithm?
Ans. The scheduling technique used by Multilevel Feedback Queue Scheduling Algorithm is:
A new job enters queue Q0 that is served FCFS. When it gains CPU, job receives 8 milliseconds. If it does not finish in 8 milliseconds, job is moved to queue Q1.
At Q1 job is again served FCFS and receives 16 additional milliseconds. If it still does not complete, it is preempted and moved to queue Q2.
Several queues arranged in some priority order.
Each queue could have a different scheduling discipline/ time quantum.
Figure: Multilevel Feedback Queue Scheduling
Q1. Explain Multilevel Feedback Queue Scheduling.
Ans. Before multilevel feedback scheduling algorithm, we used only multilevel scheduling algorithm which was not so flexible, but this one uses separate queue for handling the processes, it automatically adjust the priority of the process. If the priority is high and the process will be allotted to lower priority queue, then automatically it can switch to the higher priority queue.
For example:
One queue may implement round robin algorithm the other may use first come fir serve algorithm, the allocation is based on the type of process, and that is, the process is either of CPU bound to I/O bound etc.
This type of scheduling allows the process to move between the various queues. The idea is to implement aging. The process that takes too much CPU time is assigned with lower priority queues, in addition to the process that waits too long for processing and is assigned to higher priority.
Q3. What are the scheduling techniques used by Multilevel Feedback Queue Scheduling Algorithm?
Ans. The scheduling technique used by Multilevel Feedback Queue Scheduling Algorithm is:
A new job enters queue Q0 that is served FCFS. When it gains CPU, job receives 8 milliseconds. If it does not finish in 8 milliseconds, job is moved to queue Q1.
At Q1 job is again served FCFS and receives 16 additional milliseconds. If it still does not complete, it is preempted and moved to queue Q2.
Several queues arranged in some priority order.
Each queue could have a different scheduling discipline/ time quantum.
Figure: Multilevel Feedback Queue Scheduling
Q1. Explain Multilevel Feedback Queue Scheduling.
Ans. Before multilevel feedback scheduling algorithm, we used only multilevel scheduling algorithm which was not so flexible, but this one uses separate queue for handling the processes, it automatically adjust the priority of the process. If the priority is high and the process will be allotted to lower priority queue, then automatically it can switch to the higher priority queue.
For example:
One queue may implement round robin algorithm the other may use first come fir serve algorithm, the allocation is based on the type of process, and that is, the process is either of CPU bound to I/O bound etc.
This type of scheduling allows the process to move between the various queues. The idea is to implement aging. The process that takes too much CPU time is assigned with lower priority queues, in addition to the process that waits too long for processing and is assigned to higher priority.
What are the parameters of Multilevel Feedback Queue Scheduler?
Ans. Multilevel feedback queue scheduler defined by the following parameters:
- Number of queues.
- Scheduling algorithm for each queue.
- Method used to determine when to upgrade a process.
- Method used to determine when to denote a process.
- Method used to determine which queue a process will enter when that process needs service.
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