Efficient implementation of Multilevel Feedback Queue Scheduling

In CPU scheduling various algorithms exist like FCFS (First come first serve), SJF (Shortest job first), SRTF (Shortest remaining time first), Priority Scheduling, Round Robin (RR), MLQ (Multilevel queue), MLFQ (Multilevel feedback queue) scheduling. Multilevel Feedback Queue (MLFQ) algorithm allows the switching of processes between queues depending on their burst time. The processes switch to the next queue when burst time is greater than time quantum. Each queue can define its own scheduling policy. In this paper we have implemented MLFQ technique using small burst time for the first queue thus making it analogous to RR scheduling and using SJF prior to RR from second queue onwards gives better CPU utilization. Dynamic time quantum is also used which further improves the efficiency of the scheduling. Here the dynamic time quantum of the queues is calculated based on the burst time of the processes. Time quantum of the second queue is the burst time of the (2n/3) ^th process (where n is the number of processes remaining after the execution in the first queue) and time quantum of the third queue is burst time of the largest remaining process. Thus 66% of the processes get executed in the second queue and remaining processes in the last queue thus preventing the problem of starvation of huge burst time processes.