CPU Scheduling Algorithms and Techniques

CPU Scheduling: Understanding Different Algorithms and Techniques

Computer processors require instructions from the operating system before they can execute tasks. These instructions determine how the processor will manage time, resources, and tasks. This is where CPU scheduling comes into play. CPU scheduling is a mechanism used by the operating system to decide which task must be executed next by the processor out of all those ready to run. In this article, we'll discuss different types of CPU scheduling algorithms and techniques, including FCFS (First-Come, First-Served), SJF (Shortest Job First), Round Robin, Priority Scheduling, and Multi-Level Queue Scheduling.

First-Come, First-Served (FCFS)

The simplest algorithm for CPU scheduling is FCFS. It selects processes in the order in which they arrive in the ready queue. Processes wait until their turn, and each process runs until it completes its job. While FCFS is simple and easy to implement, it has several shortcomings. For instance, if some processes have longer execution times than others, they may remain idle while waiting for their turn, leading to increased waiting times overall.

Shortest Job First (SJF)

The SJF technique involves executing jobs in the order of decreasing job size. A smaller job is given higher priority over larger jobs. This algorithm ensures that shorter jobs get executed first and helps reduce average waiting time. However, it lacks fairness because larger jobs take longer to complete, potentially delaying other jobs. Furthermore, it does not consider execution time estimates, so it cannot handle bursty processes or changing arrival rates effectively.

Round Robin

Round Robin is another common CPU scheduling algorithm. It allocates equal time intervals called time slices between processes in the ready queue. Each process gets a chance to execute during these fixed intervals, which makes it more equitable compared to other algorithms. Since each process gets a guaranteed time slice, it prevents any one process from monopolizing the CPU. However, it may result in high overhead due to context switching, which is the frequent saving and restoring of the state of a process.

Priority Scheduling

Priority scheduling assigns priorities to processes based on certain criteria such as resource requirements, current demand, or user-defined preferences. The CPU scheduler uses these priorities to decide which process receives access first. One common approach is the Earliest Deadline First (EDF) algorithm, which assigns a priority to each process based on the time remaining until its deadline. The process with the earliest deadline gets the highest priority, ensuring that time-critical tasks are given precedence.

Multi-Level Queue Scheduling

Multi-level queue scheduling is an extension of priority scheduling that uses multiple queues with different priority levels. Processes are placed in different queues based on their priority, and the CPU scheduler selects processes from the highest-priority queue. This algorithm allows for more control over process scheduling and can be more efficient in managing different types of processes with varying resource requirements.

In conclusion, CPU scheduling algorithms play a crucial role in managing CPU resources and ensuring efficient task execution. Each algorithm has its strengths and weaknesses, and their choice depends on the specific requirements of the system being implemented. Understanding these algorithms and their trade-offs can help system administrators make informed decisions about the scheduling algorithm to use in different scenarios.