In an operating system, a CPU scheduler is a component responsible for selecting processes from the ready queue and assigning them to the CPU for execution. There are different types of CPU schedulers, and they differ in their scheduling policies and algorithms.
The primary goal of a CPU scheduler is to achieve good system performance by optimizing CPU utilization, throughput, response time, and fairness.
Here are some of the commonly used CPU scheduling algorithms:
1. First-Come, First-Served (FCFS): In this scheduling algorithm, processes are selected in the order they enter the ready queue. The process that arrives first gets executed first. FCFS is a non-preemptive algorithm, which means that once a process is assigned to the CPU, it runs to completion, and only then another process is selected.
2. Shortest Job First (SJF): In this scheduling algorithm, processes with the shortest expected processing time are given priority. SJF is also a non-preemptive algorithm, which means that once a process is assigned to the CPU, it runs to completion, and only then another process is selected.
3. Round Robin (RR): In this scheduling algorithm, each process is assigned a fixed time slice or quantum, and the CPU switches between processes in a cyclic manner, giving each process a chance to execute for a fixed amount of time. If a process does not complete execution within its time slice, it is preempted, and the CPU switches to the next process in the queue.
4. Priority Scheduling: In this scheduling algorithm, each process is assigned a priority, and the CPU selects the process with the highest priority for execution. If two or more processes have the same priority, then the scheduling algorithm may use FCFS or SJF as a tiebreaker.
5. Multilevel Feedback Queue: This scheduling algorithm uses multiple queues with different priorities and time slices. Processes are initially assigned to the highest priority queue, and if a process does not complete its execution within its time slice, it is demoted to a lower priority queue. Similarly, if a process completes its execution within its time slice, it is promoted to a higher priority queue.