Last Updated on May 26, 2023 by Prepbytes
MLQ scheduling is designed to handle situations where processes have different levels of priority or belong to different categories. It divides the ready queue, which contains all the processes waiting to be executed, into multiple separate queues, each with its own scheduling algorithm and priority level. The higher priority queues are given preference in accessing the CPU, while the lower priority queues receive CPU time only when higher priority queues are empty.
MLFQ (Multilevel Feedback Queue) is a CPU scheduling algorithm that operates based on the principle of multiple queues with different priorities and time quantum values. MLFQ is designed to handle the dynamic behavior of processes and adaptively adjust their priorities based on their resource requirements and execution patterns. It aims to strike a balance between fairness and efficiency in CPU utilization.
What is Multilevel Queue Scheduling?
In multilevel queue scheduling, all the processes are assigned permanently to the queue at the time of entry. Processes will not move between queues and it may happen that the processes in the queue can be divided into different classes where classes have their own scheduling. For example, interactive process and batch process.
The main advantage of multilevel queue scheduling is that the processes are permanently assigned to the queue.
For example let’s take three different processes:
- System process
- Interactive process
- Batch process
- In system processes the CPU itself has their own process to run which is called system process.
- In an interactive process there should be the same type of interaction.
- Batch processing is a technique of the operating system which collects the programs and data in the form of a batch before the starting of the process.
Advantages of Multilevel Queue Scheduling:
- As MLQ assigns permanent queue to the processes therefore, it has an advantage of low scheduling overhead.
- We can use MLQ to apply different scheduling methods to distinct processes.
Disadvantages of MQL Scheduling:
- Some processes may face starvation as higher priority queues are never becoming empty.
- MQL is inexorable in nature.
Multilevel Feedback Queue scheduling:
In multilevel feedback scheduling, the processes are allowed to move in between the queues, the idea behind is to separate the processes with different CPU – burst characteristics. If any process uses too much CPU then it’ll be moved to the lower priority queue and if a process waiting too much for the CPU is moved to the high priority queue this prevents starvation. Multilevel feedback queue is the most general scheme and also the most complex.
Advantages of MLFQ:
- MLFQ allows different processes to move between different queues.
- It prevents starvation.
- MLFQ is more flexible.
| Multilevel queue scheduling(MLQ) | Multilevel feedback queue scheduling(MLFQ) |
|---|---|
| In MLQ processes are assigned permanently into the queues. | In MLFQ processes are not assigned permanently to the queues. |
| Processes are divided on the basis of their priorities or size. | Processes are divided on the basis of CPU burst characteristics. |
| In this, queues are classified into two groups, background processes and foreground processes. | In this, queues are classified as higher priority queue and lower priority queue. |
| In MLQ priority is fixed. | In MLFQ priority is dynamic as processes are allowed to move between the queues. |
| As processes are not allowed to move in between queues therefore it has low scheduling overhead and is inflexible. | As in MLFQ processes are allowed to move in between queues therefore it has high scheduling overhead and is flexible. |
Conclusion In conclusion, MLQ (Multi-Level Queue) and MLFQ (Multilevel Feedback Queue) are two CPU scheduling algorithms that aim to efficiently manage the execution of processes in an operating system.
Both MLQ and MLFQ have their advantages and can be effective in different scenarios. MLQ is suitable when processes have distinct priority levels or types, whereas MLFQ is more adaptable to handle varying resource demands and dynamic behavior. MLFQ’s ability to dynamically adjust priorities and incorporate aging and priority boosting makes it more flexible in managing the CPU scheduling process.
Ultimately, the choice between MLQ and MLFQ depends on the specific requirements and characteristics of the system, such as the types of processes, fairness considerations, and the desired trade-off between responsiveness and resource utilization. Both algorithms contribute to improving CPU scheduling efficiency in multitasking operating systems.
Frequently Asked Questions
Q1. What is the main difference between MLQ and MLFQ CPU scheduling algorithms? Ans. The main difference lies in their approach to managing process priorities and adaptability. MLQ divides the ready queue into separate queues with fixed priorities, while MLFQ uses multiple queues with varying priorities that can dynamically change based on process behavior and resource requirements.
Ans. 2. Which algorithm provides better fairness in CPU scheduling? Ans. MLFQ is generally considered to provide better fairness in CPU scheduling. It incorporates priority boosting and aging mechanisms to prevent starvation of lower priority processes and allows them to move up in priority over time.
Q3. Which algorithm is more suitable for systems with different process types? Ans. MLQ is more suitable for systems with different process types because it allows processes to be categorized into separate queues based on their types or priorities. Each queue can have its own scheduling algorithm, optimizing the execution for different categories of processes.
Q4. Can MLQ and MLFQ be combined or used together in a system? Ans. Yes, MLQ and MLFQ can be combined or used together in a system. In fact, some systems employ a hybrid approach where MLFQ is used as the main scheduling algorithm, and within each MLFQ queue, MLQ scheduling is applied to further categorize and manage processes.
Q5. Which algorithm is more efficient in utilizing CPU resources? Ans. The efficiency of CPU resource utilization depends on the specific system and workload characteristics. MLQ is generally considered to be more efficient in utilizing CPU resources when processes have distinct priorities, as it ensures higher priority processes get executed first. However, MLFQ’s adaptability and dynamic adjustment of priorities can also lead to efficient utilization by preventing long-term starvation of lower-priority processes.
Q6. Can MLQ and MLFQ algorithms handle real-time processes? Ans. Both MLQ and MLFQ algorithms can handle real-time processes, but they may need additional modifications or extensions to guarantee specific real-time requirements, such as meeting deadlines or ensuring predictable response times. Real-time scheduling often requires specialized algorithms beyond the scope of MLQ and MLFQ.