CPU Scheduling Criteria in Operating Systems

CPU Scheduling Criteria in Operating Systems –

CPU scheduling in an operating system is the process of determining which process gets to use the CPU at any given time. The goal of CPU scheduling is to achieve efficient and fair allocation of the CPU’s processing time among the various processes in the system.

CPU Scheduling Criteria in Operating Systems

Several criteria and algorithms are used to make these decisions, and they vary depending on the specific goals and requirements of the system. Here are some common CPU scheduling criteria in operating systems:

1. CPU Utilization: Maximizing CPU utilization is often a primary goal. The scheduler aims to keep the CPU busy as much as possible to ensure that it’s not idle.
2. Throughput: Throughput is a measure of how many processes can be completed in a given time period. Schedulers try to maximize the number of processes completed per unit of time.
3. CPU Burst Time: This is the time a process spends using the CPU to perform computations or calculations. It represents the time the process is actively executing instructions on the CPU. CPU burst times are usually relatively short.
4. Turnaround Time: Turnaround time is the total time taken to execute a process, including both waiting time and execution time. The scheduler may aim to minimize this time to ensure that processes complete quickly.
5. Waiting Time: Waiting time is the amount of time a process spends waiting in the ready queue before getting CPU time. Minimizing waiting time is desirable to provide a responsive system.
6. Response Time: Response time is the time it takes for a system to respond to a user’s request. Interactive systems aim to minimize response time to ensure a smooth user experience.
7. Completion Time (CT): Completion time is the time at which a process finishes its execution.
8. Fairness: Fairness is the equitable distribution of CPU time among competing processes. Schedulers aim to give each process a fair share of CPU time, which is essential in multi-user or multi-tasking systems.
9. Priority: Some systems allow processes to have priorities assigned to them. The scheduler may give precedence to higher-priority processes, which is important for real-time systems and critical tasks.
10. Preemption: Preemption refers to the ability of the scheduler to stop a running process and switch to another process. Preemptive scheduling is often used in real-time and multi-tasking systems to ensure that high-priority processes are not starved of CPU time.
11. CPU-bound vs. I/O-bound: The scheduler may consider the nature of processes (whether they are CPU-bound or I/O-bound) to make scheduling decisions. For example, I/O-bound processes might be given priority to reduce their wait times.
12. Aging: Aging is a technique to prevent starvation. Processes that have been waiting for a long time are given higher priority, ensuring that they eventually get CPU time.

The choice of which scheduling criteria to prioritize and the specific scheduling algorithm used depends on the operating system’s design goals and the type of workload it is expected to handle. Different scheduling algorithms, such as First-Come-First-Serve (FCFS), Round Robin, Shortest Job First (SJF), Priority Scheduling, and Multilevel Queue Scheduling, are used to achieve these criteria to varying degrees.