Multilevel Feedback Queue Scheduling (MLFQ) CPU Scheduling


MLFQ Programming is an instance of CPU scheduling technique that works through preserving several queues based on priority, each with a distinct time quantum. The delay period of those with greater importance queues is shorter, whereas the duration period of the ones with lower importance holds is longer.

When a fresh procedure emerges, it is assigned to the top of the importance queue. The timer for the CPU chooses the most significant operation from the most important queue and allocates the processing power to it. The procedure is permitted to continue for a set amount of time or as long as it is completed, whatever comes first. If the task finishes prior to the duration of the period running out, the processor's scheduler moves on to the next task in the queue.

MLFQ Use Cases

The CPU scheduling method, Multilevel Feedback Queue (MLFQ) scheduling allocates procedures goals according to how they operate and changes those priorities on the fly. Listed below provide a few instances of MLFQ CPU programming in real-time.

  • Interactive Applications − For applications which require quick reaction instances, MLFQ is a good fit. Think about an internet browser with several tabs active as an example. A distinct handle is represented by every screen. Although background tabs obtain less attention, MLFQ can give the currently active tab more importance, making sure that users have a pleasant experience through rapidly completing its assignments

  • Video Rendering − MLFQ is frequently implemented in video rendering programmes to order real-time processing of video tasks. Video encoding and decoding operations can be handled in a high-priority queue to ensure lag-free listening and effective execution. Non-real-time assignments like reading and writing files and background-providing operations can be handled in additional queues with lower priorities

  • Real-Time Systems − MLFQ can also be used in real-time systems in which assignments must complete in a specific amount of time. Examples of simultaneous operations include detector tracking, gathering data, and control algorithms in a production control framework. In order to guarantee prompt execution and adhere to pressing system time constraints, MLFQ can prioritise control procedures that call for quick responses

  • Gaming Application − MLFQ is frequently used in gaming applications to enhance the experience of playing. Background duties like listening to audio or communicating via the network are able to be considered a lower importance while time-critical assignments such as providing video game structures, handling input from players, and physics computations might be given greater importance. This guarantees that regardless of periods of high resource usage, the game continues to be adaptable and run effortlessly

Important Points

If the allotted quantum runs out beforehand the procedure is finished, it is delayed and shifted into the following queue. The process that needs execution is then chosen from the list of processes with the highest priority. This procedure is repeated as long as the procedure is finished or it attains the lowest level of the queue.

MLFQ scheduling, along with preempting procedures depending on their duration quantum, employs aging methods to guarantee that good-running procedures are ultimately given an opportunity to execute. Since its position of importance rises as it utilizes a longer period within a lower-priority queue. This guarantees that long waiting processes ultimately move into a higher-priority list and receive CPU time.


In contemporary platforms, Multilevel Feedback Queue (MLFQ) established as an instruction set algorithm for scheduling has multiple benefits. Among the benefits are −

  • Improved Response Time − MLFQ scheduling improves the reaction speed of procedures by giving immediate attention to short tasks with the shortest waiting time.

  • Good Throughput − MLFQ scheduling uses aging methods to ensure that long-running processes receive adequate CPU power. This balancing mechanism allows for the CPU to be fully utilized

  • Dynamic Priority Adjustment − MLFQ scheduling automatically adjusts the priority of a process based on its behavior. Processes that require less CPU power can be moved to lower priority queues, while CPU-intensive tasks can be moved to higher priority queues

  • Efficient Use of CPU − MLFQ scheduling optimizes CPU utilization by preempting a process when it's allocated time quantum expires.

  • Scalability − MLFQ scheduling is scalable and capable of handling a large number of processes simultaneously. It can effectively manage a high workload without sacrificing system performance.

  • Easy to Implement − MLFQ scheduling is relatively easy to implement as it only requires specific data structures to maintain multiple queues with different priorities.


In contemporary platforms, Multilevel Feedback Queue (MLFQ) established as an instruction set algorithm for scheduling has multiple benefits along with few drawbacks. Among them are −

  • Complexity − MLFQ scheduling is a complex technique that requires the management of multiple queues with different priorities and time quantum for each queue. This complexity makes it more challenging to implement and maintain compared to simpler scheduling approaches

  • Priority Inversion −There is a possibility of priority inversion in MLFQ scheduling, where a lower-priority process holds a resource that a higher priority process requires, causing the higher-priority process to wait.

  • Overhead − MLFQ scheduling has a higher overhead because the scheduling algorithm needs to constantly track and adjust the priority order of processes within each queue. This overhead can result in decreased performance.

  • Poor Predictability − The unpredictable nature of MLFQ scheduling makes it difficult to accurately predict the completion time of processes.


MLFQ scheduling impacts an appropriate equilibrium among the requirements of both multimedia and programs, which makes it a good fit for general-purpose platforms. Alternative scheduling algorithms, including Shortest Job First (SJF), Priority Scheduling, and Round Robin (RR), may be better suited for specific tasks or assignments. The final decision on the scheduling method for the CPU is based on the machine's particular requirements and the compromises that must be made among multiple variables that include reaction time, productivity, equity, accuracy, and complexity.

Updated on: 26-Jul-2023


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