Round Robin Scheduling Algorithm

Round Robin Scheduling Algorithm 

The round-robin (RR) scheduling algorithm is designed especially for time-sharing systems. It is similar to FCFS scheduling, but pre-preemption is added to switch between processes. A small unit of time, called a time quantum or time slice, is defined. A time quantum is generally from 10 to 100 milliseconds. The ready queue is treated as a circular queue.

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It is one of the oldest, simplest, and fairest and most widely used scheduling algorithms, designed especially for time-sharing systems. A small unit of time, called time-slice or quantum, is defined. All runnable processes are kept in a circular queue. The CPU scheduler goes around this queue, allocating the CPU to each process for a time interval of one quantum. New processes are added to the tail of the queue.

CPU : Central Processing Unit

C program for solving round robin

Algorithm  :   without arrival time

#include<stdio.h>

void main()

   {

      int j,q,i,n,ts;

      int aw;                        //total waiting time      

      float awt;                     //average waiting time

      int bt[10],wt[10],te[10],rt[10];j=0; clrscr();

      printf("enter number of process :\t");

      scanf("%d",&n);

      printf("\n enter brust time \n");

      for(i=0;i<n;i++)

       {

                printf("P%d\t",i+1);

                scanf("%d",&bt[i]);

                rt[i]=bt[i];

                te[i]=0;     wt[i]=0;                

       }  

     printf("\n enter time slice\t");

     scanf("%d",&ts); q=0;   clrscr();

     printf("\nprocess      :")  ;

     for(i=0;i<n;i++) 

       {

             printf("  %d",i+1);

       }

     printf("\nBrust time   :");

     for(i=0;i<n;i++)

          {

              printf("  %d",bt[i]);

          }

     printf("\n Gaint chart \n");

     while(j<=n)

         {
            j++;

           for(i=0;i<n;i++)

                 {

                     if(rt[i]==0)  continue;

                     if(rt[i]>ts) 

                            {

                                 printf("\n %d\t P%d",q,i+1);

                                 q=q+ts;

                                 rt[i]=rt[i]-ts;

                                 te[i]=te[i]+1;

                            }

                     else
                           {

                                printf("\n %d\t P%d",q,i+1);

                                wt[i]=q-te[i]*ts;  

                                q=q+rt[i];
                                 rt[i]=rt[i]-rt[i];

                            }

                 }

          }                                               //end of while loop
     awt=0;

     printf("\n Process   Waitnig time");

     for(i=0;i<n;i++) 

         {

              printf("\n P%d      :   %d",i+1,wt[i]); awt=awt+wt[i];

         }
     aw=awt;

     printf("\ntotal waiting time %d",aw);

     printf("\n Avg wainting time %f ",awt/n);

     getch();

  }

OUTPUT:-

Burst Time is actually time that is required to complete execution of particular task or process.