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SCHEDULING ALGORITHMS
This document discusses different types of scheduling algorithms used by operating systems to determine which process or processes will run on the CPU. It describes preemptive and non-preemptive scheduling, and provides examples of common scheduling algorithms like first-come, first-served (FCFS), shortest job first (SJF), round robin, and priority-based scheduling. Formulas for calculating turnaround time and waiting time are also presented.
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An overview of scheduling algorithms prepared by Dhaval Sakhiya and Prakash Asadiya.
Definition of scheduling with CPU and processes; introduces preemptive and non-preemptive scheduling.
Explains preemptive scheduling: interruption of processes, time quantum, and process selection.
Explains non-preemptive scheduling: process completion requirements and operation details.
Describes long-term, medium-term, and short-term schedulers and their functions in CPU scheduling.
Discusses process and thread interchangeability, and the scheduling state transitions of processes.
Formulas for calculating Turnaround Time (TAT) and Waiting Time (WT) essential in scheduling.
Details on FCFS scheduling, where processes are served in the order they arrive.
Indicates SJF as an efficient scheduling method to minimize waiting time with implementation challenges.
Example of SJF non-preemptive scheduling with process arrival and burst times, showcasing optimality.
Illustrates an example of preemptive SJF scheduling with arrival and burst times for processes.
Explains Round Robin scheduling with time quantum and context switching for process execution.
Describes priority-based scheduling, where processes are executed based on assigned priority.
Example of non-preemptive priority scheduling with illustrated process execution and timelines.
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SCHEDULING ALGORITHMS
- 1. SCHEDULING ALGORITHMS PREPARED BY :DHAVAL SAKHIYA(13CSE533) PRAKASH ASADIYA(13CSE501)
- 2. What is scheduling? One CPU with a number of processes. Only one process can use the CPU at a time which process is going to be execute that thing decide a by scheduler and it’s whole thing is called scheduling. Two types of scheduling: 1. Preemptive 2.Non- Preemptive
- 3. Preemptive : i. Inpreemptive scheduling, the currently running process may be interrupted and move to the ready state by OS(forcefully). ii. It selects a process and lets it run for a specific time duration, called time quantum. iii. If process is still running at the end of the time interval, it is suspended and the scheduler selects another process to run.
- 4. Non-Preemptive : i. Innon-preemptive scheduling, the running process can only lose the processor voluntarily by terminating or by requesting and I/O. OR, once CPU given to a process it can not be preempted until the process completes its CPU burst. ii. It selects a process to run and then just lets it run until it blocks or terminates.
- 5. Types of scheduler Long-term scheduler: load a job in memory Runs infrequently Medium-term scheduler: Select ready process to run on CPU Should be fast Short-term scheduler: Reduce multiprogramming or memory consumption
- 6. Process Scheduling • “process”and “thread” used interchangeably • Which process to run next • Many processes in “ready” state New Ready Running Exit Waiting
- 7. FORMULA : TURNAROUND TIME: TAT=(Waiting Time)(W.T) + (Burst Time)(B.T) OR = (Completion Time)(C.T) – (Arrival Time)(AT) WAITING TIME: WT=(Turn Around Time)(TAT) – (Burst Time)(B.T) OR =(Completion Time)(C.T) – (Arrival Time)(A.T) – (Burst Time)(B.T)
- 8. First-Come First-Serve (FCFS) One ready queue; OS runs the process at head of the queue; New processes come in at the end of the queue; Running process does not give up the CPU until it terminates or it performs IO.
- 10. Shortest Job First(SJF) Best approach to minimize waiting time. Impossible to implement. Processer should know in advance how much time process will take.
- 11. SJF isoptimal – gives minimum average waiting time for a given set of processes. Process Arrival Time Burst Time P1 0 7 P2 2 4 P3 4 1 P4 5 4 SJF (non-preemptive): 0 7 8 12 16
- 12. P1 P2 P3P2 P4 P1 Example of Preemptive SJF Process Arrival Time Burst Time P1 0 7 P2 2 4 P3 4 1 P4 5 4 SJF (preemptive) 0 2 4 5 7 11 16
- 13. Round Robin Scheduling Each process is provided a fix time to execute called quantum. Once a process is executed for given time period. Process is preempted and other process executes for given time period. Context switching is used to save states of preempted processes.
- 15. Priority Based Scheduling Each process is assigned a priority. Process with highest priority is to be executed first and so on. Processes with same priority are executed on first come first serve basis. Priority can be decided based on memory requirements, time requirements or any other resource requirement.
- 16. Priority based nonpre-preemptive Algo Example 0 P4 P2 P1 P3 6 9 14 17