Highest Response Ratio Next (HRRN) Scheduling

Prerequisite –

Given n processes with their Arrival times and Burst times, the task is to find average waiting time and average turn around time using HRRN scheduling algorithm.
The name itself states that we need to find the response ratio of all available processes and select the one with the highest Response Ratio. A process once selected will run till completion.

Criteria – Response Ratio

Mode – Non-Preemptive

 

Response Ratio = (W + S)/S

Here, W is the waiting time of the process so far and S is the Burst time of the process.
Performance of HRRN

Shorter Processes are favoured.

1.      Aging without service increases ratio, longer jobs can get past shorter jobs

 

 

 

 

Explanation

§  At t = 0 we have only one process available, so A gets scheduled.

§  Similarly at t = 3 we have only one process available, so B gets scheduled.

§  Now at t = 9 we have 3 processes available, C, D and E. Since, C, D and E were available after 4, 6 and 8 units respectively. Therefore, waiting time for C, D and E are (9 – 4 =)5, (9 – 6 =)3, and (9 – 8 =)1 unit respectively.

§  Using the formula given above we calculate the Response Ratios of C, D and E respectively as 2.25, 1.6 and 1.5.

§  Clearly C has the highest Response Ratio and so it gets scheduled

§  Next at t = 13 we have 2 jobs available D and E.

§  Response Ratios of D and E are 2.4 and 3.5 respectively.

§  So process E is selected next and process D is selected last.

Implementation of HRRN Scheduling

1.      Input the number of processes, their arrival times and burst times.

2.      Sort them according to their arrival times.

3.      At any given time calculate the response ratios and select the appropriate process to be scheduled.

4.      Calculate the turn around time as completion time – arrival time.

5.      Calculate the waiting time as turn around time – burst time.

6.      Turn around time divided by the burst time gives the normalized turn around time.

7.      Sum up the waiting and turn around times of all processes and divide by the number of processes to get the average waiting and turn around time.

Code

#include <stdio.h>

 

// Defining process details

struct process {

    char name;

    int at, bt, ct, wt, tt;

    int completed;

    float ntt;

} p[10];

 

int n;

 

// Sorting Processes by Arrival Time

void sortByArrival()

{

    struct process temp;

    int i, j;

 

    // Selection Sort applied

    for (i = 0; i < n - 1; i++) {

        for (j = i + 1; j < n; j++) {

 

            // Check for lesser arrival time

            if (p[i].at > p[j].at) {

 

                // Swap earlier process to front

                temp = p[i];

                p[i] = p[j];

                p[j] = temp;

            }

        }

    }

}

 

void main()

{

    int i, j, t, sum_bt = 0;

    char c;

    float avgwt = 0, avgtt = 0;

    n = 5;

 

    // predefined arrival times

    int arriv[] = { 0, 2, 4, 6, 8 };

 

    // predefined burst times

    int burst[] = { 3, 6, 4, 5, 2 };

 

    // Initializing the structure variables

    for (i = 0, c = 'A'; i < n; i++, c++) {

        p[i].name = c;

        p[i].at = arriv[i];

        p[i].bt = burst[i];

 

        // Variable for Completion status

        // Pending = 0

        // Completed = 1

        p[i].completed = 0;

 

        // Variable for sum of all Burst Times

        sum_bt += p[i].bt;

    }

 

    // Sorting the structure by arrival times

    sortByArrival();

    printf("\nName\tArrival Time\tBurst Time\tWaiting Time");

    printf("\tTurnAround Time\t Normalized TT");

    for (t = p[0].at; t < sum_bt;) {

 

        // Set lower limit to response ratio

        float hrr = -9999;

 

        // Response Ratio Variable

        float temp;

 

        // Variable to store next processs selected

        int loc;

        for (i = 0; i < n; i++) {

 

            // Checking if process has arrived and is Incomplete

            if (p[i].at <= t && p[i].completed != 1) {

 

                // Calculating Response Ratio

                temp = (p[i].bt + (t - p[i].at)) / p[i].bt;

 

                // Checking for Highest Response Ratio

                if (hrr < temp) {

 

                    // Storing Response Ratio

                    hrr = temp;

 

                    // Storing Location

                    loc = i;

                }

            }

        }

 

        // Updating time value

        t += p[loc].bt;

 

        // Calculation of waiting time

        p[loc].wt = t - p[loc].at - p[loc].bt;

 

        // Calculation of Turn Around Time

        p[loc].tt = t - p[loc].at;

 

        // Sum Turn Around Time for average

        avgtt += p[loc].tt;

 

        // Calculation of Normalized Turn Around Time

        p[loc].ntt = ((float)p[loc].tt / p[loc].bt);

 

        // Updating Completion Status

        p[loc].completed = 1;

 

        // Sum Waiting Time for average

        avgwt += p[loc].wt;

        printf("\n%c\t\t%d\t\t", p[loc].name, p[loc].at);

        printf("%d\t\t%d\t\t", p[loc].bt, p[loc].wt);

        printf("%d\t\t%f", p[loc].tt, p[loc].ntt);

    }

    printf("\nAverage waiting time:%f\n", avgwt / n);

    printf("Average Turn Around time:%f\n", avgtt / n);

}

 

Output

 

 

Name    Arrival Time    Burst Time    Waiting Time    TurnAround Time     Normalized TT

A        0        3        0        3        1.000000

B        2        6        1        7       1.166667

C        4        4        5        9        2.250000

E        8        2        5        7        3.500000

D        6        5        9        14        2.800000

Average waiting time:4.000000

Average Turn Around time:8.000000