# Highest Response Ratio Next (HRRN) CPU Scheduling

• Difficulty Level : Easy
• Last Updated : 14 Nov, 2022

Given N processes with their Arrival times and Burst times, the task is to find average waiting time and an 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.

## Characteristics of HRRN CPU Scheduling:

• Highest Response Ratio Next is a non-preemptive CPU Scheduling algorithm and it is considered as one of the most optimal scheduling algorithm.
• The criteria for HRRN is Response Ratio, and the mode is Non-Preemptive.
• HRRN is basically considered as the modification of Shortest Job First in order to reduce the problem of starvation.
• In comparison with SJF, during HRRN scheduling algorithm, the CPU is allotted to the next process which has the highest response ratio and not to the process having less burst time.

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.

## Advantages of HRRN CPU Scheduling

• HRRN Scheduling algorithm generally gives better performance than the shortest job first Scheduling.
• There is a reduction in waiting time for longer jobs and also it encourages shorter jobs.

## Disadvantages of HRRN CPU Scheduling

• The on ground implementation of HRRN scheduling is not possible as it is not possible know the burst time of every job in advance.
• In this scheduling, there may occur overload on the CPU.

## Performance of HRRN –

• Shorter Processes are favoured.
• Aging without service increases ratio, longer jobs can get past shorter jobs.

Let us consider the following examples.

Example-1: Consider the following table of arrival time and burst time for four processes P1, P2, P3, P4 and P5.

The Highest Response Ratio Next CPU Scheduling Algorithm will work on the basis of steps as mentioned below:

At time= 0,

• Available Processes: P1, Hence P1 starts executing till its completion.

At time = 2,

• Available Processes: P1, P2
• But P1 keep executing as HRRN is a non-preemptive algorithm and thus it will finish its execution

At time = 3,

• Process P1 finish its execution
• Process P2 starts executing as it is only process available.

At time = 4,

• Process P3 arrives and wait for process P2 to execute
• Process P2 continue its execution

At time = 6,

• Process P4 arrives and wait for the process P2 to execute

At time = 8,

• Process P5 arrives and wait for its execution in the ready queue

At time = 9,

• Process P2 completes its execution
• Now there are 3 processes available, P3, P4 and P5. Since, P3, P4, P5 were available after 4, 6 and 8 units respectively.
• Therefore, waiting time for P3, P4 and P5 are (9 – 4 =)5, (9 – 6 =)3, and (9 – 8 =)1 unit respectively.
• Using the formula given above,  (Response Ratio = (W + S)/S) calculate the Response Ratios of P3, P4 and P5 respectively as 2.25, 1.6 and 1.5.
• Clearly, P3 has the highest Response Ratio and so it gets scheduled

At time = 13,

• Available Processes: P4 and P5
• Response Ratios of P4 and P5 are 2.4 and 3.5 respectively using the above formula.
• Clearly, P5 has the highest Response Ratio and so it gets scheduled

At time = 15,

• After completion of process P5, Process P4 is selected at last and execute till it gets finished

At time = 20,

• Process P4 will finish its execution.
• The overall execution of the processes will be as shown below:

Gantt Chart –

Since, completion time (C.T) can be directly determined by Gantt chart, and

Turn Around Time (TAT)
= (Completion Time) – (Arrival Time)

Also, Waiting Time (WT)
= (Turn Around Time) – (Burst Time)

Therefore, final table look like,

Output:

Total Turn Around Time = 40 ms
So, Average Turn Around Time = 40/5 = 8.00 ms

And, Total Waiting Time = 20 ms
So, Average Waiting Time = 20/5 = 4.00 ms

Implementation of HRRN Scheduling –

• Input the number of processes, their arrival times and burst times.
• Sort them according to their arrival times.
• At any given time calculate the response ratios and select the appropriate process to be scheduled.
• Calculate the turn around time as completion time – arrival time.
• Calculate the waiting time as turn around time – burst time.
• Turn around time divided by the burst time gives the normalized turn around time.
• 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.

Below is the implementation of above approach:

## C++

 `// C++ program for Highest Response Ratio Next (HRRN)``// Scheduling``#include ``using` `namespace` `std;``// 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;``            ``}``        ``}``    ``}``}` `int` `main()``{``    ``int` `i, j, sum_bt = 0;``    ``char` `c;``    ``float` `t, 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();``    ``cout << ``"PN\tAT\tBT\tWT\tTAT\tNTT"``;``    ``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 process 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;``        ``cout << ``"\n"` `<< p[loc].name << ``"\t"` `<< p[loc].at;``        ``cout << ``"\t"` `<< p[loc].bt << ``"\t"` `<< p[loc].wt;``        ``cout << ``"\t"` `<< p[loc].tt << ``"\t"` `<< p[loc].ntt;``    ``}``    ``cout << ``"\nAverage waiting time: "` `<< avgwt / n << endl;``    ``cout << ``"Average Turn Around time:"` `<< avgtt / n;``}``// This code is contributed by shivi_Aggarwal`

## C

 `// C program for Highest Response Ratio Next (HRRN) Scheduling``#include ` `// 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 process 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);``}`

## Python3

 `# Python3 program for Highest Response Ratio``# Next (HRRN) Scheduling` `# Function to sort process by arrival time``def` `sortByArrival(at, n):``    ` `    ``# Selection Sort applied ``    ``for` `i ``in` `range``(``0``, n ``-` `1``):``        ``for` `j ``in` `range``(i ``+` `1``, n):``            ` `            ``# Check for lesser arrival time ``            ``if` `at[i] > at[j]:``                ` `                ``# Swap earlier process to front``                ``at[i], at[j] ``=` `at[j], at[i]` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ` `    ``sum_bt ``=` `0``    ``avgwt ``=` `0``    ``avgTT ``=` `0``    ``n ``=` `5``    ` `    ``completed ``=``[``0``] ``*` `n``    ``waiting_time ``=` `[``0``] ``*` `n``    ``turnaround_time ``=` `[``0``] ``*` `n``    ``normalised_TT ``=` `[``0``] ``*` `n``    ` `    ``# Predefined arrival times ``    ``arrival_time ``=` `[ ``0``, ``2``, ``4``, ``6``, ``8` `]``    ` `    ``# Predefined burst times ``    ``burst_time ``=` `[ ``3``, ``6``, ``4``, ``5``, ``2` `]``    ``process ``=` `[]``    ` `    ``# Initializing the structure variables ``    ``for` `i ``in` `range``(``0``, n):``        ``process.append(``chr``(``65` `+` `i))``        ``sum_bt ``+``=` `burst_time[i]``        ` `    ``# Sorting the structure by arrival times ``    ``sortByArrival(arrival_time, n)``    ``print``(``"Name"``, ``"Arrival time"``,``          ``"Burst time"``, ``"Waiting Time"``,``          ``"Turnaround "``, ``"Normalized TT"``)``    ``t ``=` `arrival_time[``0``]``    ` `    ``while``(t < sum_bt):``        ` `        ``# Set lower limit to response ratio ``        ``hrr ``=` `-``9999``        ``temp, loc ``=` `0``, ``0``        ` `        ``for` `i ``in` `range``(``0``, n):``            ` `            ``# Checking if process has arrived``            ``# and is Incomplete ``            ``if` `arrival_time[i] <``=` `t ``and` `completed[i] !``=` `1``:``                ` `                ``# Calculating Response Ratio ``                ``temp ``=` `((burst_time[i] ``+``                        ``(t ``-` `arrival_time[i])) ``/``                         ``burst_time[i])``                         ` `                ``# Checking for Highest Response Ratio ``                ``if` `hrr < temp:``                    ` `                    ``# Storing Response Ratio ``                    ``hrr ``=` `temp``                    ` `                    ``# Storing Location``                    ``loc ``=` `i``                    ` `        ``# Updating time value ``        ``t ``+``=` `burst_time[loc]``        ` `        ``# Calculation of waiting time``        ``waiting_time[loc] ``=` `(t ``-` `arrival_time[loc] ``-``                                 ``burst_time[loc])``        ` `        ``# Calculation of Turn Around Time ``        ``turnaround_time[loc] ``=` `t ``-` `arrival_time[loc]``        ` `        ``# Sum Turn Around Time for average ``        ``avgTT ``+``=` `turnaround_time[loc]``        ` `        ``# Calculation of Normalized Turn Around Time ``        ``normalised_TT ``=` `float``(turnaround_time[loc] ``/``                              ``burst_time[loc])``        ` `        ``# Updating Completion Status``        ``completed[loc] ``=` `1``        ` `        ``# Sum Waiting Time for average ``        ``avgwt ``+``=` `waiting_time[loc]``        ` `        ``print``(process[loc], ``"\t\t"``, arrival_time[loc],``              ``"\t\t"``, burst_time[loc], ``"\t\t"``,``              ``waiting_time[loc], ``"\t\t"``,``              ``turnaround_time[loc], ``"\t\t"``,``              ``"{0:.6f}"``.``format``(normalised_TT))` `    ``print``(``"Average waiting time: {0:.6f}"``.``format``(avgwt ``/` `n))``    ``print``(``"Average Turn Around time:  {0:.6f}"``.``format``(avgTT ``/` `n))` `# This code is contributed by etcharla revanth rao`

Output

```PN    AT    BT    WT    TAT    NTT
A    0    3    0    3    1
B    2    6    1    7    1.16667
C    4    4    5    9    2.25
E    8    2    5    7    3.5
D    6    5    9    14    2.8
Average waiting time: 4
Average Turn Around time:8```

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