7. Consider a proposed process scheduler that uses a characteristics: multilevel

Question

7. Consider a proposed process scheduler that uses a characteristics: multilevel feedback queueing network with the following a) The quantum in the first level is 0.5ms. b) Th are five levels and each lower level has a quantum twice the size of the quantum at the previous level. cess cannot be preempted until its quantum expires ere The system runs background and interactive jobs. At times, jobs may be CPU-bound or 1/O bound processe What problem(s) might this scheme cause and what minimal changes would you suggest?

Explanation / Answer

Suppose there is 100 process with 0.2ms executing multiple times and a single process with 10ms.Now,each of 100 process completes its execution in the given time quantum of 0.5ms at level 1(1 is first level).Now consider process with 10ms time gets a chance and executed 0.5ms.So,there are still 9.5ms burst time remaining.As a result of this its priority reduced and shifted to level 2.Now each 100 process will be executed first and then this remaining 9.5ms will be executed.So,waiting time for this big process become very high.

So,basically the problem is A proccess in lower priority queue suffers from starvation due to some short process in higher priority level.

Solution : Increase the priority of process in the lower priority queue at regular time interval.So these process can get up to higher level (level 1) so it become a higher priority process and gets chance to be executed.This process is called Aging.

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