Prerequisite – CPU Scheduling, Multilevel Queue SchedulingThis Scheduling is prefer Multilevel Queue(MLQ) Scheduling yet in this process can move between the queues. Multilevel Feedback Queue Scheduling (MLFQ) keeps examining the habits (time that execution) of processes and according to which it alters its priority. Now, look at the diagram and also explanation listed below to recognize it properly.
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Now permit us intend that queues 1 and 2 follow round robin with time quantum 4 and 8 respectively and also queue 3 monitor FCFS. One implementation of MFQS is given listed below –
When a procedure starts executing climate it first enters queue 1.In queue 1 procedure executes for 4 units and also if it completes in this 4 unit or it gives CPU for I/O operation in this 4 unit then the priority of this process does not change and if the again comes in the ready queue then it again starts its execution in Queue 1.If a procedure in queue 1 go not finish in 4 devices then that priority gets reduced and it shifted to queue 2.Above clues 2 and 3 are also true because that queue 2 processes however the time quantum is 8 units.In a general case if a procedure does not complete in a time quantum climate it is change to the lower priority queue.In the last queue, processes are booked in one FCFS manner.A procedure in a lower priority queue can only execute only when greater priority queues are empty.A process running in the reduced priority queue is interrupted by a procedure arriving in the greater priority queue.Well, the above implementation may differ for instance the last queue can likewise follow Round-robin Scheduling.Problems in the above implementation – A procedure in the reduced priority queue have the right to suffer indigenous starvation as result of some brief processes acquisition all the CPU time.Solution – A an easy solution have the right to be to boost the priority of every the processes after consistent intervals and place them all in the highest priority queue.What is the need for such complex Scheduling?Firstly, the is more flexible than multilevel queue scheduling.To optimize turnaround time algorithms favor SJF are essential which need the running time of procedures to schedule them. However the running time of the process is not recognized in advance. MFQS operation a procedure for a time quantum and also then that can change its priority(if that is a lengthy process). Thus it learns from past behavior of the procedure and climate predicts that future behavior. This means it tries to run a shorter process very first thus optimizing come back time.MFQS additionally reduces the an answer time.Example –Consider a mechanism that has actually a CPU-bound process, which needs a explode time the 40 seconds. The multilevel Feed back Queue scheduling algorithm is used and the queue time quantum ‘2’ seconds and also in every level that is incremented through ‘5’ seconds. Then how many times the process will it is in interrupted and also on which queue the procedure will terminate the execution?Solution –Process P demands 40 secs for total execution.At Queue 1 the is executed for 2 seconds and then interrupted and also shifted come queue 2.At Queue 2 that is executed because that 7 seconds and then interrupted and shifted come queue 3.At Queue 3 the is executed because that 12 seconds and also then interrupted and shifted to queue 4.At Queue 4 the is executed for 17 seconds and then interrupted and shifted to queue 5.At Queue 5 the executes because that 2 seconds and then the completes.Hence the process is interrupted 4 times and completes top top queue 5.Advantages:It is much more flexible.It enables different procedures to move in between different queues.It stays clear of starvation by moving a procedure that waits too lengthy for the lower priority queue come the greater priority queue.
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Disadvantages:For the selection of the finest scheduler, it calls for some other method to pick the values.It produces much more CPU overheads.It is the most complicated algorithm.This article is added by Ashish Sharma. If you prefer starrkingschool.net and also would favor to contribute, you can also write an article using write.starrkingschool.net or mail your article to review-team
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