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Multilevel Feedback Queue Scheduling or Multilevel Adaptive Scheduling

 

To solve the problem multilevel feedback queue scheduling, allows a process to move between queues.

 

The idea is to separate processes according to the characteristics of their CPU bursts. If a process uses too much CPU time, it will be moved to a lower-priority queue. This scheme leaves I/O-bound and interactive processes in the higher-priority queues. In addition, a process that waits too long in a lower-priority queue may be moved to a higher-priority queue. This form of aging prevents starvation.

 

Fig: 19 

 

In general, a multilevel feedback queue scheduler is defined by the following parameters:

 

The number of queues.  

→ The scheduling algorithm for each queue.

→ The method used to determine when to upgrade a process to a higher priority queue.

→ The method used to determine when to demote a process to a lower priority queue.

→ The method used to determine which queue a process will enter when that process needs service.