Operating System

Explain about multilevel queue scheduling ?

Multilevel queue scheduling (MLQ) is a CPU scheduling method that organizes tasks into queues based on priority, and then assigns each group of processes a queue. Each queue has its own priority level, with higher-priority processes in higher-priority queues. The processes are then assigned to a queue based on their characteristics, such as memory size, process priority, or process type. A scheduler periodically checks the queues for waiting tasks and allocates processor resources accordingly. 

In MLQ, the ready queue is divided into different queues based on process properties like memory size, process priority, or process type. The appropriate level is then assigned to the processes based on their characteristics, such as priority, memory requirements, and CPU usage. For example, the foreground queue might be scheduled by the Round Robin algorithm, while the background queue is scheduled by an FCFS algorithm. 

MLQ does not permit moving processes of different priorities or types between queues. For example, no batch process could run until interactive and system queues are empty. 

MLQ has several advantages, including:

  • Users can apply different scheduling methods to every queue to distinguish the processes.
  • The scheduling overhead is very low. 

In MLQ, batch processes are allocated resources based on their priority, but they are generally given lower priority compared to interactive processes. For example, a standard division of processes is between a foreground (interactive) process and a background (batch) process. 

Multilevel feedback queue (MLFQ) is a similar CPU scheduling algorithm to MLQ, but in MLFQ, processes can move between queues. This makes MLFQ more efficient than MLQ. MLFQ also has the following characteristics:

  • Flexibility: MLFQ is more flexible than MLQ.
  • Turnaround time: MLFQ optimizes turnaround time by learning from a process’s past behavior and predicting its future behavior.
  • Response time: MLFQ reduces response time

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