A Comparative Study on PBRR CPU Scheduling Algorithm for Different Time Quantum and Priority

Abstract

CPU Scheduling is one of the fundamental concepts of Operating System [4]. Most CPU scheduling algorithms concentrate on maximizing CPU utilization and throughput and minimizing turnaround time, waiting time, response time and number of context switching for a set of requests. Some of the popular CPU scheduling algorithms are First-Come-First-Served (FCFS), Shortest Job First (SJF), Priority Based (PB) and Round Robin (RR). Round Robin is the most popular choice in time shared system, but it may not be suitable for real time systems because of larger waiting time, turnaround time and more number of context switches [7, 8]. As processor is the important resource, CPU scheduling becomes very important in accomplishing the operating system (OS) design goals [5]. In this paper we have discussed scheduling criteria, viz.; CPU Utilization, Throughput, Waiting Time, Turnaround Time and Response Time and different types of scheduler, viz.; short-term, mid-term and long-term scheduler. We have also discussed the working principles of existing scheduling algorithms, viz.; FCFS, SJF, ED and RR. In this paper we have discussed CPU scheduling algorithm called PBRR (Priority Based Round Robin), which is based on traditional RR algorithm. We have also done a comparative analysis on the performance on scheduling criteria for PBRR scheduling algorithm through twenty five different cases where we take five different time quantum, such as 1ms, 2ms, 3ms, 4ms and 5ms under the five different priority ranges for each time quantum. At the end we have analysed the changes of average waiting time, average turnaround time and number of context switches over different time quantum.