Simulation of 3 CPU Scheduling Algorithms

CPU scheduling algorithms represent the core mechanism in operating systems for determining process execution order, and simulating these algorithms helps us deeply understand their operational principles and performance differences. This article discusses the simulation implementation and key metric analysis of three classical scheduling algorithms: Shortest Job First (SJF), Highest Response Ratio Next (HRRN), and Round Robin (RR).

Shortest Job First (SJF) The SJF algorithm prioritizes processes with the shortest execution time. This algorithm effectively reduces average waiting time, but relies on accurate prediction of process execution times, making it challenging to implement in practical systems. In simulation, we maintain a ready queue and select the process with the shortest remaining execution time each time until completion. Key metrics include response time (R), CPU utilization (U), and system throughput (S). The implementation typically involves sorting processes by their burst time and using a min-heap data structure for efficient selection.

Highest Response Ratio Next (HRRN) HRRN is an improved version of SJF that avoids starvation problems by comprehensively considering both waiting time and execution time. The response ratio is calculated using the formula: (Waiting Time + Execution Time) / Execution Time. During simulation, we select the process with the highest response ratio each time, ensuring fair scheduling for long jobs. HRRN generally achieves a good balance between throughput and fairness. The algorithm implementation requires tracking each process's waiting time and dynamically updating response ratios during scheduling decisions.

Round Robin (RR) The RR algorithm employs fixed time slices to execute each ready process in rotation, making it suitable for time-sharing systems. Simulation requires setting the time quantum size and cycling through processes in the queue. The algorithm's performance highly depends on time slice selection: too small causes frequent context switching, reducing CPU efficiency; too large degenerates into First-Come-First-Served (FCFS). RR provides good fairness but may result in higher average waiting times. Code implementation typically uses a circular queue structure with timer interrupts to manage time slices.

Key Performance Metrics Response Time (R): Duration from process arrival to first CPU allocation CPU Utilization (U): Ratio of CPU productive working time to total simulation time System Throughput (S): Number of completed processes per unit time These metrics can be calculated during simulation by maintaining timestamps for process events and aggregating statistical data.

By comparing these three algorithms through simulation, we can more intuitively understand their applicability in different scenarios. For example, SJF performs excellently in batch processing systems, while RR is more suitable for interactive systems. The simulation code typically involves process control blocks, queue management, and metric collection modules to accurately represent each algorithm's behavior.