CPU Scheduling Algorithm

Various CPU Scheduling Algorithm

1Bindu Singh

1Assistant Professor (CSE)

Vadodara Institute of Engineering, Vadodara (VIE)

Abstract: This paper explains a various C P U scheduling algorithms used in operating system. In a multiprogrammng environement multiple processes or threads competing for the CPU at the same time. If at a time only one process can run then we have to select which process to run next. The part of the operating system that takes this the decision is called the scheduler, and the algorithm it uses is called the scheduling algorithm.

Keywords:CPU scheduling,scheduler,scheduling Algorithms, Turnaround time, Waiting Time, Response Time, Burst Time.

1. INTRODUCTION

The assignment

Many parameters are used to evaluate the scheduling algorithm. Some commonly used scheduling criteria are described below.

1. CPU Utilization Scheduling Criteria:

The CPU must be busy as much as possible to perform different activities. The percentage of time, the CPU is executing a process may range from 0 to 100 percent. CPU utilization is very important in real time and multiprogramming system. In a real time system the CPI utilization should be 50 percent (lightly loaded system) to 95 percent (heavily loaded system). It means that load on a system affects the CPU utilization. The high CPU utilization is achieved on heavily loaded system.

2. Balanced Utilization Scheduling Criteria:

Balanced utilization represents the percentage of the time al the resource utilized. In addition to considering he CPU utilization the utilization of memory, I/O devices and other system resources are also considered.

3. Through Put Scheduling Criteria:

The number of process executed by the system in a specific period of time this time unit is called through put. For long process this rate may be one process per minute. Similarly for short process, it may be 100 processes per minute. The evaluation of through must be considered on the basis of average

New processes go to the end of the queue. When the scheduler needs to run a process, it picks the process that is at the head of the queue. This scheduler is non-preemptive. If the process has to block on I/O, it enters the waiting state and the scheduler picks the process from the head of the queue. When I/O is complete and that waiting (blocked) process is ready to run again, it gets put at the end of the queue

2. Round Robin

Round robin scheduling is a preemptive version of first-come, first-served scheduling. Processes are dispatched in a first-in-first-out sequence but each process is allowed to run for only a limited amount of time. This time interval is known as a time-slice or quantum. If a process does not complete or get blocked because of an I/O operation within the time slice, the time slice expires and the process is preempted. This preempted process is placed at the back of the run queue where it must wait for all the processes that were already in the queue to cycle through the CPU.

3. Shortest remaining time first