Multilevel Feedback Queue Scheduling

Multilevel feedback queue-scheduling algorithm allows a process to move between queues. It uses many ready queues and associate a different priority with each queue.

The Algorithm chooses to process with highest priority from the occupied queue and run that process either preemptively or unpreemptively. If the process uses too much CPU time it will moved to a lower-priority queue. Similarly, a process that wait too long in the lower-priority queue may be moved to a higher-priority queue may be moved to a highest-priority queue. Note that this form of aging prevents starvation.

Example:

Figure 5.7 pp. 140 in Sinha

  • A process entering the ready queue is placed in queue 0.
  • If it does not finish within 8 milliseconds time, it is moved to the tail of queue 1.
  • If it does not complete, it is preempted and placed into queue 2.
  • Processes in queue 2 run on a FCFS basis, only when queue 2 run on a FCFS basis, only when queue 0 and queue 1 are empty.`
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