Scheduling Algorithms-R.D.Sivakumar
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This document discusses various CPU scheduling algorithms. It describes non-preemptive and preemptive scheduling and covers scheduling algorithms like first-come first-served (FCFS), shortest job first (SJF), priority scheduling, round robin, multi-level queue scheduling, and multi-processor scheduling. It provides details on how each algorithm works and its advantages and disadvantages.
Scheduling Algorithms-R.D.Sivakumar
- 1. Video Lecture and E-Content Created by R.D.SIVAKUMAR,M.Sc.,M.Phil.,M.Tech., Assistant Professor of Computer Science & Assistant Professor and Head, Department of M.Com.(CA), Ayya Nadar Janaki Ammal College, Sivakasi – 626 124. Mobile: 099440-42243 e-mail : [email protected] website: www.rdsivakumar.blogspot.in SCHEDULING ALGORITHMS
- 2. CPU Scheduling algorithms decide which of the processes in the ready queue is to be allocated to the CPU. CPU SCHEDULING ALGORITHMS
- 3. Non Pre-emptive scheduling Pre-emptive scheduling. CPU SCHEDULING TYPES
- 4. Once the CPU has been allocated . In non-preemptive scheduling the process keeps the CPU until it releases the CPU either by terminating or by switching to the waiting state. NON-PRE-EMPTIVE SCHEDULING
- 5. In pre-emptive scheduling, the process keeps the CPU until interrupt occurs. PRE-EMPTIVE SCHEDULING
- 6. It is Simplest CPU scheduling algorithm It is non-preemptive scheduling algorithm In this scheme, the process that requests the CPU first is allocated the CPU first (or) the process enter the ready queue first is served first. FIRST-COME, FIRST SERVED SCHEDULING
- 7. Waiting time Waiting time = starting time – arrival time Turn around time Turn around time= finished time – arrival time (Burst time + waiting time). Response time In non preemptive scheduling algorithm, the average waiting time is equal to the average response time. FCFS
- 8. In this scheme, the CPU is assigned to the process that has the smallest next CPU burst. It may be either preemptive (or) non preemptive. SHORTEST JOB FIRST SCHEDULING
- 9. In preemptive shortest job first, the new process may have a shorter next CPU burst than the currently executing process, it will preempt the currently executing process. Preemptive SJF scheduling is some times called “Shortest- remaining-time-first Scheduling”. PREEMPTIVE SJF SCHEDULING ALGORITHM
- 10. Comparing to FCFS algorithm, almost 50% waiting time saved in SJF. ADVANTAGES
- 11. Big jobs are waiting so much time for CPU. DISADVANTAGES
- 12. In this scheme, a priority is associated with each process and the CPU is allocated to the process with the highest priority. Equal priority processes are scheduled in FCFS order. Priorities are indicated by range of numbers. Low numbers represent the high priority It may be either preemptive or non preemptive PRIORITY SCHEDULING ALGORITHM
- 13. In preemptive priority scheduling algorithm, the new process may have higher priority than the currently executing process, it will preempt the currently executing process. PREEMPTIVE PRIORITY SCHEDULING ALGORITHM
- 14. It is a preemptive scheduling algorithm. It is designed for time sharing systems. In round robin scheduling, the ready queue is treated as a circular queue. In this scheduling, the CPU switches between the processes when the time quantum expires. ROUND ROBIN SCHEDULING
- 15. In this algorithm, the ready queue is partitioned with number of ready queue. Each ready queue has its own scheduling algorithm. MULTI LEVEL QUEUE SCHEDULING
- 16. System process Fore ground process Background process Student process FOUR READY QUEUE PARTITIONS
- 17. The system process might be scheduled by an FCFS algorithm. SYSTEM PROCESS
- 18. Foreground process is also known as interactive process. It is might be scheduled by an short jump first algorithm. FOREGROUND PROCESS
- 19. Background process is also known as batch process. It is might be scheduled by an round robin algorithm. BACKGROUND PROCESS
- 20. Student process might be scheduled by an SRJ algorithm. STUDENT PROCESS
- 21. In this scheme, the ready queue is divided into number of queues. It allows a process to move between processes. ADVANTAGES A process that waits too long into a lower-priority queue may be moved to a higher priority queue. MULTI LEVEL FEEDBACK QUEUE SCHEDULING
- 22. In multi processor scheduling, each processor examines the common ready queue and selects a process to execute. MULTI PROCESSOR SCHEDULING