A Comparative Study of CPU Scheduling Algorithms for Efficient Process Management

Abstract

CPU scheduling is a fundamental component of operating system design, ensuring that computational resources are allocated optimally among multiple processes. This paper examines the concepts and methods used in CPU scheduling, focusing on major algorithms like First-Come, First-Served (FCFS), Shortest Job Next (SJN), Round Robin (RR), and Priority Scheduling. Through a detailed comparison of performance metrics including waiting time, turnaround time, and CPU utilization, we examine how these algorithms perform under varying system loads and requirements. The study reveals the trade-offs between simplicity and efficiency, highlighting the advantages of pre-emptive methods in dynamic environments and the challenges faced by non-pre-emptive approaches. Finally, the paper discusses the potential of hybrid and adaptive scheduling techniques, emphasizing their role in meeting the demands of modern, multi-core systems. These results offer meaningful insights into improving CPU efficiency in modern operating systems.

Introduction

In a single-processor system, only one process executes at a time, leaving the CPU idle during I/O waits. Multiprogramming addresses this by keeping multiple processes in memory and switching the CPU to ready processes, maximizing CPU utilization. CPU scheduling—a core operating system function—determines the execution order of processes to optimize performance metrics such as CPU utilization, throughput, turnaround time, waiting time, response time, and fairness.

Processes move through various states: New, Ready, Running, Blocked/Waiting, Terminated, and suspended states (Ready/Wait) for memory management. CPU scheduling algorithms can be preemptive or non-preemptive, and common types include:

• FCFS (First-Come, First-Served): Simple FIFO, but may cause long waits (convoy effect).

• SJF (Shortest Job First): Minimizes average waiting time but can starve long tasks.

• LJF (Longest Job First): Executes longest tasks first, may increase waiting time.

• Priority Scheduling: Executes higher-priority tasks first; risk of starvation.

• Round Robin (RR): Preemptive, assigns fixed time slices, ensuring fairness.

• SRTF (Shortest Remaining Time First), LRTF (Longest Remaining Time First), HRRN, Multilevel Queue, and MLFQ: Advanced or dynamic algorithms to balance fairness, responsiveness, and efficiency.

Each algorithm has advantages and trade-offs related to efficiency, fairness, and system responsiveness. Modern systems require hybrid and adaptive scheduling to handle multi-core processors, real-time applications, and dynamic workloads effectively.

Conclusion

Efficient CPU scheduling is essential for enhancing the performance and effectiveness of operating systems. By effectively managing the order and allocation of CPU time among various processes, it ensures maximum utilization of resources, minimizes waiting times, and enhances overall system throughput. Each scheduling criterion, such as turnaround time, waiting time, and response time, addresses specific aspects of system performance, highlighting the need for tailored algorithms based on the requirements of different applications. The research demonstrates that while traditional algorithms like FCFS, SJF, and Round Robin have laid the foundation for CPU scheduling, modern trends such as hybrid and adaptive approaches are paving the way for more dynamic and efficient systems. However, challenges such as handling dynamic workloads and ensuring fairness across processes remain areas for further exploration. Many contemporary computer systems support multiple processors and allow each processor to schedule itself independently. Typically, each processor maintains its own private queue of processes (or threads), all of which are available to run. Additional issues related to multiprocessor scheduling include processor affinity, load balancing, and multicore processing. A real-time computer system requires that results arrive within a deadline period; results arriving after the deadline has passed are useless. Hard real-time systems must guarantee that real-time tasks are serviced within their deadline periods. Soft real-time systems are less restrictive, assigning real-time tasks higher scheduling priority than other tasks. Real-time scheduling algorithms include rate-monotonic and earliest deadline-first scheduling. Rate-monotonic scheduling assigns tasks that require the CPU more often a higher priority than tasks that require the CPU less often. Earliest-deadline-first scheduling assigns priority according to upcoming deadlines—the earlier the deadline, the higher the priority. Proportional share scheduling divides up processor time into shares and assigning each process several shares, thus guaranteeing each process a proportional share of CPU time. The POSIX Pthread API provides various features for scheduling real-time threads as well. Operating systems supporting threads at the kernel level must schedule threads—not processes—for execution. This is the case with Solaris and Windows. Both systems schedule threads using pre-emptive, priority-based scheduling algorithms, including support for real-time threads. The Linux process scheduler uses a priority-based algorithm with real-time support as well. The scheduling algorithms for these three operating systems typically favour interactive over CPU-bound processes. In conclusion, selecting the right CPU scheduling algorithm is crucial for achieving a balance between efficiency, predictability, and system responsiveness, making it an essential focus for ongoing research and development in operating systems.

References

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Copyright

Copyright © 2025 Khushboo .. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.