CPU Scheduling

Introduction

In an operating system, CPU scheduling plays a crucial role in managing the execution of processes. It determines the order in which processes are allocated CPU time, ensuring efficient utilization of the CPU and providing a fair allocation of resources. This topic covers the basic concepts of CPU scheduling, various scheduling algorithms, algorithm evaluation, multiple processor scheduling, and real-world applications.

Basic Concepts of CPU Scheduling

CPU scheduling involves the selection of processes from the ready queue and allocating them CPU time. There are two types of CPU scheduling: preemptive and non-preemptive. Preemptive scheduling allows a process to be interrupted and moved out of the CPU, while non-preemptive scheduling does not allow interruptions.

The criteria used for evaluating CPU scheduling algorithms include CPU utilization, throughput, turnaround time, waiting time, and response time.

Scheduling Algorithms

1. First-Come, First-Served (FCFS) Scheduling

FCFS scheduling is a non-preemptive algorithm that allocates CPU time to processes in the order they arrive. It has the advantage of simplicity but can lead to poor performance if long processes arrive first.

1. Shortest Job Next (SJN) Scheduling

SJN scheduling is a non-preemptive algorithm that selects the process with the shortest burst time. It minimizes the average waiting time but requires knowledge of the burst time in advance.

1. Round Robin (RR) Scheduling

RR scheduling is a preemptive algorithm that allocates a fixed time slice to each process in a circular manner. It ensures fairness but may result in high context switching overhead.

1. Priority Scheduling

Priority scheduling assigns priorities to processes and allocates CPU time to the highest priority process. It can be preemptive or non-preemptive.

1. Multilevel Queue Scheduling

Multilevel queue scheduling categorizes processes into multiple queues based on priority. Each queue can have its own scheduling algorithm.

Algorithm Evaluation

Scheduling algorithms are evaluated based on metrics such as CPU utilization, throughput, turnaround time, waiting time, and response time. Performance evaluation involves comparing the algorithms using real-world workload traces or simulations. The selection of an appropriate algorithm depends on the specific requirements of the system.

Multiple Processor Scheduling

Multiple processor scheduling involves allocating processes to multiple CPUs in a system. There are two types of multiple processor scheduling: asymmetric multiprocessing and symmetric multiprocessing. Load balancing techniques are used to distribute the workload evenly across the processors.

Real-World Applications and Examples

CPU scheduling is essential in various domains, including operating systems, cloud computing, and real-time systems. In operating systems, CPU scheduling ensures efficient utilization of resources. In cloud computing, it enables the allocation of virtual machines to physical servers. In real-time systems, it guarantees timely execution of critical tasks.

Advantages and Disadvantages of CPU Scheduling

CPU scheduling offers several advantages, such as improved CPU utilization, enhanced system performance, and fair allocation of resources. However, it also has disadvantages, including overhead and complexity, the possibility of starvation, and difficulty in predicting execution time.

Conclusion

In conclusion, CPU scheduling is a critical aspect of operating systems that determines the order in which processes are allocated CPU time. Understanding the basic concepts, various scheduling algorithms, and their evaluation is essential for efficient resource management. The selection of an appropriate algorithm depends on the specific requirements of the system and can greatly impact system performance.

Summary

CPU scheduling is a crucial aspect of operating systems that determines the order in which processes are allocated CPU time. This topic covers the basic concepts of CPU scheduling, various scheduling algorithms, algorithm evaluation, multiple processor scheduling, and real-world applications. It discusses the advantages and disadvantages of CPU scheduling and emphasizes the importance of selecting an appropriate scheduling algorithm.

Analogy

Imagine a restaurant with multiple tables and a single chef. The chef needs to decide which table to serve next based on certain criteria. The chef can follow different scheduling algorithms, such as serving the customers in the order they arrived (FCFS), serving the table with the fewest customers (SJN), or serving each table for a fixed amount of time (RR). The choice of algorithm affects the overall efficiency and fairness of the restaurant.