CPU Scheduling

CPU scheduling is a process which allows one process to use the CPU while the execution of another process is on hold(in waiting state) due to unavailability of any resource like I/O etc, thereby making full use of CPU. The aim of CPU scheduling is to make the system efficient, fast and fair.


Scheduling Criteria

CPU utilization

– keep the CPU as busy as possible

Throughput

– no. of processes that complete their execution per time unit

Turnaround time

– amount of time to execute a particular process

Waiting time

– amount of time a process has been waiting in the ready queue

Response time

– amount of time it takes from when a request


Scheduling Algorithm Optimization Criteria

Max CPU utilization
Max throughput
Min turnaround time
Min waiting time
Min response time


Scheduling Algorithms

First in first out
Shortest remaining time
Fixed priority (pre-emptive) scheduling
Round-robin scheduling
Multilevel queue scheduling


Overview

Scheduling algorithm CPU Overhead Throughput Turnaround time Response time
First In First Out Low Low High Low
Shortest Job First Medium High Medium Medium
Priority based scheduling Medium Low High High
Round-robin scheduling High Medium Medium High
Multilevel Queue scheduling High High Medium Medium




Quantitative Aptitude
Reasoning
Programming
Interview