Question

Part I: Theory In this part you need to discuss different process scheduling algorithm. The main points to include in your project are: 1. Goals of processor scheduling. 2. Preemptive vs. nonpreemptive scheduling. 3. Priorities in scheduling. 4. Common scheduling algorithms. First-In-First Out (FIFO) Round Robin (RR) Shortest-Process-First (SPF)

Answer 1

PROCESSOR SCHEDULING:-

WHEN?

1. WHEN PROCESS IS GOING FROM RUNNING STATE TO TERMINATION STATE

2. When the process is going from Running state to Wait/block/IO state

3. When the process is going from Running state to Ready State due to pre-emption

4. When the process is going from Wait state to ready state due to high priority

Functionality:-

To allocate the CPU for  the process execution

GOAL:-

i) Increase the Cpu utilization and throughput of the system

ii) Minimize the average Waiting time, Average turn around time of the processes.

In preemptive scheduling, A process in running state can be fetched out called as context switching in ready state and another process from the ready state gets chance in running state at any time either the process in running state is completed its execution or not.pre-emption of the process can be done at any time. usually, pre-emption happens when high priorities process arrives in the ready state.

Whereas in Case of Nonpreemptive scheduling once a process gets inside the running state it will not leave the running state until its complete its execution no matter either high priority process arrives in a ready state or not.

Priorities in scheduling are set just for giving a process more important than other processes and if a process has higher priority then it gets chance to be in running state for execution as compared to processes with low priority.

1. First in first out(FIFO):-

This scheduling algorithm is based on the criteria of ARRIVAL TIME i.e Process with low arrival time will be executed first in Running state. And it also uses the Non-preemptive mode of scheduling.

If the arrival time of the processes is the same then schedule the process which has the lowest processId.

In FIFO, If the process is having large Burst time then it will have a drastic effect on the average waiting time of all the processes. This effect is called Convoy effect.

2. Round Robin(RR):-

In Round Robin, there is a term used QUANTUM or TIME SLICE i.e a time slice or quantum time is set and Every process will be executed till that time slice one by one. (for example, if there are two processes and quantum time is 1 sec then the first process will execute for 1 sec and then the second process will execute for 1 sec and again the first process will execute for 1 sec and so on till all processes complete its execution).

It uses the preemptive mode of scheduling

If the time quantum is very very large then RR degenerates to FIFO algorithm

RR is used to decrease the Response time.

3. Shortest process First(SPF):-

This scheduling algorithm is based on the criteria of Burst TIME i.e Process with low Burst time will be executed first in Running state. And it also uses the Non-preemptive mode of scheduling.

If the Burst time of the processes is the same then schedule the process which has the lowest arrival time.

If the arrival time of the processes is the same then schedule the process which has the lowest processId.