Difference between Multi Level Queue (MLQ) Scheduling and Round Robin (RR) algorithms
Last Updated :
10 May, 2025
Queue Scheduling refers to the process of managing and organizing tasks (or processes) that need to be executed by a system. In an operating system, tasks are often placed in queues waiting for CPU to execute them. Queue scheduling helps the system decide which task to run next, and in what order, ensuring efficient and fair use of CPU.
Multi Level Queue Scheduling (MLQ)
Multilevel Queue(MLQ) CPU scheduling is a type of scheduling that is applied at the operating system level with the aim of sectioning types of processes and then being able to manage them properly. As with the MQ Series, processes are grouped into several queues using MLQ based on known parameters such as priority, memory, or type. Every queue has its scheduling policy and processes that are in the same queue are very similar too.
Generally, the topmost level of queue has the highest priority which decreases as we move to the lower levels. If the upper level has an absolute priority over lower levels then it is non-preemptive else if the time slice is divided between various queues then it becomes preemptive in nature.
MLQAdvantages of Multilevel Queue CPU Scheduling
- Customizable: The scheduling algorithm can be customized to meet the specific requirements of different types of processes.
- Prioritization: Priorities are assigned to processes based on their type, characteristics, and importance, which ensures that important processes are executed in a timely manner.
Disadvantages of Multilevel Queue CPU Scheduling
- Some processes may starve for CPU if some higher priority queues are never becoming empty.
- It is inflexible in nature.
- There may be added complexity in implementing and maintaining multiple queues and scheduling algorithms.
Round Robin
Round Robin Scheduling is a method used by operating systems to manage the execution time of multiple processes that are competing for CPU attention. It is called round robin because the system rotates through all the processes, allocating each of them a fixed time slice or quantum, regardless of their priority. This algorithm mainly depends on the time quantum.
Round Robin Scheduling FlowchartVery large time quantum makes RR same as the FCFS while a very small time quantum will lead to the overhead as context switch will happen again and again after very small intervals. The major advantage of this algorithm is that all processes get executed one after the other which does not lead to starvation of processes or waiting by process for quite long time to get executed.
Advantages of Round Robin Scheduling
- Fairness: Each process gets an equal share of the CPU.
- Simplicity: The algorithm is straightforward and easy to implement.
- Responsiveness: Round Robin can handle multiple processes without significant delays, making it ideal for time sharing systems.
Disadvantages of Round Robin Scheduling
- Overhead: Switching between processes can lead to high overhead, especially if the quantum is too small.
- Underutilization: If the quantum is too large, it can cause the CPU to feel unresponsive as it waits for a process to finish its time.
Difference between MLQ and Round-Robin (RR) scheduling algorithm
| Aspect | Multilevel Queue (MLQ) | Round-Robin (RR) |
|---|
| Scheduling Approach | Executes processes based on the priority of the queue and the algorithm used in that queue. | Executes each process for a fixed time quantum in a cyclic manner. |
| Preemption | Can be both preemptive and non-preemptive depending on the configuration. | Always preemptive in nature. |
| Average Waiting Time | Depends on the combination of algorithms used across multiple queues. | Generally lower and depends on the time quantum. |
| Implementation Complexity | Complex and difficult to implement. | Simple and easy to implement. |
| Starvation | Lower priority processes may suffer from starvation. | All processes get CPU time, so starvation is unlikely. |
| CPU Time Allocation | Uneven depends on queue priority and algorithm. | Fair each process gets equal CPU time in turns. |
| Overhead | Switching between queues introduces overhead. | Too small a time quantum can cause high overhead due to frequent context switches. |
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