Cheatography
https://cheatography.com
Process Scheduling in Operating System
Scheduling Queue
Job Queue :A process when enters a system is put into a job queue . |
Ready Queue: The processes residing in main memory and ready for execution are put in the ready queue. |
Device Queue: The processes waiting for a particular I/O device are put into the device queue. |
Scheduling Criteria
1. CPU Utilization: It should be maximum. 40% minimum- 90% maximum. |
2. Throughput: Number of processes that are completed per unit time are called throughput. It should be maximum. |
3. Turnaround Time: The interval from time of submission of process to time of completion. Turnaround time= period spent waiting+ready queue time+execution+I/O interrupt time. It should be minimum. |
1. First Come First Serve (FCFS)
Priority Scheduling Diagram
5. Multilevel Queue Scheduling
|
|
Scheduling Queue Diagram
Medium Term scheduler Diagram
SCHEDULING ALGORITHM
Scheduling Algorithm decides which process should the CPU be allocated to. There are six scheduling algorithms. |
First Come First Serve Shortest Job First
The process that requests for the CPU first, gets the access first. |
Each process has the length of the next CPU burst. |
FIFO queue is used in handling the process. |
The process with the smallest next CPU burst gets access to the process. |
Long waiting time for the next processes. |
Comparitively less waiting time for next process. |
It is a non-preemptive algorithm. |
It can be premptive or non-preemptive algorithm. |
Priority Scheduling Round Robin Scheduling
Each process has a priority. |
There is a fixed time quantum. |
CPU allocated to the process with higher priority. |
Ready queue is treated as a circular queue and CPU is allocated to the First process for specific time quantum. |
Problem: Starvation of low priority process.Solution: AGING |
Problem: If time quantum is too large, algorithm works as FCFS. |
It can be preemptive or non-preemptive |
It is preemptive. |
Multilevel Queue Multilevel Feedback Queue
Ready queue is divided into: Foreground (interactive) process and Background (batch) process. |
Allows the process from one queue to move to the next queue. |
Foreground implements Round Robin Scheduling. and Background implements FCFS. |
Here processes are separated according to their CPU burst. |
|
|
Scheduler
Long Term Scheduler: Also known as job scheduler selects process from disk and puts into memory. |
Short Term Scheduler: Also known as CPU scheduler select process from memory and allocates a CPU to it. |
Medium Term Scheduler: It is used to remove a process from and reduce degree of multi-programing .Later it can be re-introduced from point where it was left . This is called as swapping. |
Scheduling Criteria
4. Waiting Time: The time for which the process has to wait in the ready queue is waiting time. It should be minimum. |
5. Response Time: Time taken to respond to a process is response time. It should be minimum. |
2. Shortest Job First (SJF)
4. Round Robin Scheduling Diagram
6. Multilevel Feedback Queue Scheduling
|
Created By
Metadata
Favourited By
Comments
No comments yet. Add yours below!
Add a Comment
Related Cheat Sheets