Linear Scheduling Method in Operating System


Linear Scheduling Method is a scheduling algorithm designed for real-time systems in which tasks must be completed within specific time frames to ensure the system's proper operation. It is a straightforward algorithm that assigns tasks based on their deadlines and provides them with fixed time slices to complete their execution. In this article, we will learn about the Linear Scheduling Method its various elements, its advantages and disadvantages of usage in an Operating System

What is Linear Scheduling Method in Operating System?

The tasks in LSM are arranged in a linear order, and the scheduler moves through the list, allocating time slices to each task in turn. The length of each time slice is fixed and determined by the system and task characteristics.

The LSM allots a time slice to an action as soon as it is assigned. The task needs to get completed during this time slice. The timer moves on to the next task on the list if the present task is done before the completion of the allotted time slice. The LSM preempts the tasks that are not completed within the time slice allotted. Post this, the timetable program shifts to the next subsequent task, assigning the remainder of the time from the prior task's time slice.

LSM ensures that actions that can be scheduled are finished by the deadline. If the structure has enough assets to complete every assignment by their assigned deadlines, LSM ensures that every one of the tasks will be completed on time. However, if the system's capacities are insufficient, certain duties may fail to meet their deadlines, which leads to system problems or poor performance.

LSM has the added benefit of being straightforward and simple to implement. It's also predictable, which means scheduling decisions are based solely on time constraints and resource availability. As an outcome, it is known and capable of ensuring a minimum level of functionality in real-time systems.

However, LSM might not represent the most effective method of scheduling for every kind of system. It requires secured and well-defined deadlines for tasks, and these may not be the case for all applications. It can also be inefficient in platforms with an extensive variety of tasks or in systems that require an excessive amount of flexibility.

Elements of Linear Scheduling Method

  • Time Slices − Each task in the system is assigned a fixed time slice by LSM. The length of each time slice is determined by the system characteristics and the requirements of the tasks.

  • Task Order − LSM arranges tasks in sequential order, with each task following the one before it. The scheduler iterates through the tasks on the list, allocating time slices to each one in turn.

  • Preemption − The LSM tends to preempt those tasks that do not complete their fulfillment inside the time slice assigned. The scheduler then moves on and allocates this task’s remaining time slice to the next task.

  • Deterministic Scheduling − LSM employs a deterministic scheduling approach in which scheduling decisions are solely based on task deadlines and resource availability. This ensures the scheduling algorithm's predictability and dependability.

Advantages of the Linear Scheduling Method

  • Task Prioritizing − Tasks are prioritized based on their deadlines, with earlier deadlines receiving higher priority.

  • Time Slicing − The length of each time slice is determined by the system and task characteristics. The time slice should be long enough to allow the task to finish within the deadline but short enough to allow the scheduler to move on to the next task as soon as possible.

  • Preemption − If a task does not finish its completion within the period of time slice allocated to it, it gets preempted, as well as the scheduling system shifts on to the following task, allocating the remaining time slice from the previous task.

  • Deterministic Scheduling − The method of scheduling is known and reliable because decisions regarding scheduling solely depend on deadlines for tasks and resource availability.

  • Timekeeping − In order to guarantee that tasks get finished on time, the scheduling program tracks the time and remaining period for every task's time slice.

  • Resource Management − LSM requires that sufficient resources be available for completing every assignment by their assigned deadlines. As a consequence, asset management is vital for making sure the system has sufficient resources to complete the tasks.

Disadvantages of the Linear Scheduling Method

Although the Linear Scheduling Method (LSM) has advantages, it also has disadvantages, which are as follows −

  • Inefficient use of resources − No matter the number of hours it takes to carry out a task, LSM provides predetermined time slices to it. As a result, some tasks may finish considerably sooner than the given time slice, whereas other ones may take far more time, which leads to inadequate utilization or excessive utilization of system resources.

  • Limited flexibility − LSM is less flexible compared to other scheduling algorithms because it is a simple and predictable scheduling algorithm. It is inappropriate for dealing with fluid or erratic changes in the machine's workload and changes to the task sequence and time slice length may be required to accommodate changes.

  • Difficulty in dealing with real-time constraints − Adjusted time frames may not be competent to make sure that every assignment will meet its deadlines, so LSM may rather be suited to platforms with strict real-time constraints.

  • Priority inversion − Higher-priority tasks are carried out first in LSM, which may result in an inversion of priority for lower-priority duties if higher-priority tasks block them. As a result, lower-priority tasks can get delayed, leading to these individuals' due dates.

Although the theory of LSM is straightforward, its implementation can be challenging, particularly in structures that have numerous processing units, in which task relocation and coordination may be required.


The Linear Scheduling Method (LSM) is a straightforward and deterministic scheduling algorithm that assigns fixed time slices to each task in a linear order. LSM is well-suited for systems with well-defined characteristics and requirements, but it has limitations in terms of resource utilization, flexibility, dealing with real-time constraints, and the possibility of priority inversion. Despite its limitations, LSM can be a useful scheduling algorithm for some systems. Time slicing, task prioritization, preemption, deterministic scheduling, timekeeping, and resource management must all be carefully considered when implementing LSM.

Updated on: 03-May-2023


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