List scheduling in Operating System


List scheduling is an operating system technique for managing the execution of processes in a computer system. It entails making a list of processes to be carried out and then scheduling them based on their priority or other criteria. In this article, we will explore the necessary things to understand in List Scheduling in Operating System.

Essential points about List Scheduling in O.S

Here are some important points to remember about list scheduling in operating systems −

  • Since list scheduling is a preemptive scheduling algorithm, processes can be interrupted and rescheduled based on their priority.

  • Processes usually reside in a stack, with higher-priority procedures at the front.

  • The scheduler selects the next process in the queue to run and allocates it to processors.

  • The scheduling program may use an assortment of criteria for assessing process priority, including the quantity of CPU time the procedure previously used, the quantity of storage it requires, or how crucial it is to the task it is working on.

  • List scheduling is commonly used in systems that operate in real-time where assignments must be answered within a certain amount of time.

Process of List Scheduling in Operating System

A queue is basically used to store the list of processes, with each one of them assigned a value. The priority value is used by the scheduler for deciding which procedure should be performed in order. Higher-priority procedures are typically assigned at the first of the processing queue, later on, lower-priority procedures are arranged.

The scheduler selects the next process in the queue to execute and gives it to a processor inside. If more than one processor is accessible, the scheduler can allocate multiple processes to run at the same time. The scheduling tool also monitors the execution of the processes and may anticipate or reconsider them based on priority or additional requirements.

A number of variables influence a process's priority. This includes the amount of CPU energy it has already consumed, the quantity of RAM it requires, and the significance of the assignment it is performing. In a few cases, the scheduler may use one or more of those variables to determine process priority.

List time management is frequently utilized in systems that operate in real-time where assignments must be answered within a certain amount of time. In these systems, the scheduler has to make sure that important assignments get done quickly and that lower-priority tasks are not interfering with critical task completion.

The drawback of list scheduling is that if greater-priority methods are added to the wait indefinitely, some lower-priority processes may be starved of CPU time. Some scheduling algorithms, such as aging or round-robin scheduling, address this issue by ensuring that all procedures, irrespective of the order of importance, receive some CPU time.

List arranging can be a productive scheduling technique when it comes to resource utilization. The algorithm tries to maximize CPU utilization by maintaining it busy with process execution. This may be accomplished by reducing idle time on the processor and maintaining that all procedures are finished within as little time as possible.

In the list-based scheduling system, the scheduler selects the process that needs to be carried out from the starting point of the waiting list, which is typically the procedure with the greatest amount of priority. The selected process is subsequently assigned to the processor. When the procedure is completed, the processor can proceed to the subsequent one in the queue. This makes sure the computer's processor does not remain idle and that it is being used effectively.

Advantages of List Scheduling in Operating System

List planning can reduce queued processes' waiting time while also increasing CPU utilization. Because interprets alongside higher priority are carried out first, significant duties can be completed quickly. This is particularly relevant for real-time systems with short response times.

Since it can handle tasks with varying levels of priority, list scheduling is useful for real-time systems. Real-time systems are those in which the correctness of the system is determined not only by the results of computations but also by their timing. In other words, to function properly, real-time systems must adhere to strict deadlines.

List scheduling is able to be used to guarantee that tasks with the highest priority are completed first. This contributes to the system meeting its deadlines and completing critical tasks on time. In real-time systems, list scheduling can often be combined with additional strategies, such as deadline-driven planning or rate monotonic planning, in order to guarantee that assigned duties are completed on time.

Not only is list scheduling effective for systems that operate in real-time, but it also happens to be relatively simple to put into effect. The basic algorithm consists of maintaining on top of a list of operations, each with an importance value, and then executing the procedure with the greatest importance first. Because of the algorithm's simplicity, it is easy to put into effect in the majority of operating systems. Additionally, the procedure can be expanded to deal with situations that are more complicated, such as incorporate-processor systems or platforms with multiple tasks.

Disadvantages of List Scheduling in Operating System

List scheduling, including any other scheduling technique, has some disadvantages that may happen in specific circumstances. Some of these disadvantages include starvation, inefficiency, and rigidity.

The risk of starvation is one disadvantage of list scheduling. When a high-priority process repeatedly enters the queue, it prevents lower-priority processes from being executed. If the high-priority process never finishes, the lower-priority processes may be denied CPU time and never executed. To mitigate this risk, the scheduler may need to employ additional techniques, such as aging, to ensure that lower-priority processes are executed eventually.

Inefficiency is another potential disadvantage of list scheduling, particularly when dealing with long-running processes. Because list scheduling selects processes solely on their priority, some processes may be delayed for an extended period before being executed. If these processes run for a long time, they may consume a large amount of CPU time, leaving other processes waiting and causing the system to crash.

In terms of modifying priorities, list scheduling may additionally be rigid. once an operation has been allocated a priority, changing it without disrupting the procedure's execution may be difficult. As a result, adjusting the algorithm for scheduling on the fly in order to accommodate altering system conditions may be difficult.

To address these potential issues, alternative scheduling algorithms could be used. To ensure that every application receives a proportionate amount of CPU time, preemptive scheduling algorithms such as the round-robin or shortest job first can be used. In order to minimize the possibility of starvation and inefficiency, other techniques such as flexible priority modification or process aging can be used.


List scheduling is a method of scheduling that can be employed by operating systems to allocate CPU resources more efficiently. In this article, we learned that List Scheduling includes maintaining a list of operations, and each of these has an assigned priority price. Performing the highest priority process comes first. List scheduling can be beneficial for real-time systems with short response times, and it is easy to implement.

Updated on: 03-May-2023


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