Highest Response Ratio Next (HRRN) CPU Scheduling
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.
Processes | Arrival time | Burst Time |
---|---|---|
P1 | 0ms | 3ms |
P2 | 2ms | 6ms |
P3 | 4ms | 4ms |
P4 | 6ms | 5ms |
P5 | 8ms | 2ms |
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.
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time | Remaining Burst Time |
---|---|---|---|---|---|---|---|
0-2ms | P1 | 0ms | P1 | 2ms | 3ms | 1ms |
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
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time | Remaining Burst Time |
---|---|---|---|---|---|---|---|
2-3ms | P2 | P1 | |||||
P2 | 2ms | 0ms | 6ms | 6ms |
At time = 3,
- Process P1 finish its execution
- Process P2 starts executing as it is only process available.
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time | Remaining Burst Time |
---|---|---|---|---|---|---|---|
3-4ms | P2 | 2ms | P2 | 1ms | 6ms | 5ms |
At time = 4,
- Process P3 arrives and wait for process P2 to execute
- Process P2 continue its execution
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time | Remaining Burst Time |
---|---|---|---|---|---|---|---|
4-6ms | P2 | 2ms | P3 | P2 | 2ms | 5ms | 3ms |
P3 | 4ms | 0ms | 4ms | 4ms |
At time = 6,
- Process P4 arrives and wait for the process P2 to execute
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time | Remaining Burst Time |
---|---|---|---|---|---|---|---|
6-8ms | P2 | 2ms | P3, P4 | P2 | 2ms | 3ms | 1ms |
P3 | 4ms | 0ms | 4ms | 4ms | |||
P4 | 6ms | 0ms | 5ms | 5ms |
At time = 8,
- Process P5 arrives and wait for its execution in the ready queue
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time | Remaining Burst Time |
---|---|---|---|---|---|---|---|
8-9ms | P3, P4, P5 | P2 | |||||
P3 | 4ms | 0ms | 4ms | 4ms | |||
P4 | 6ms | 0ms | 5ms | 5ms | |||
P5 | 8ms | 0ms | 2ms | 2ms |
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
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time | Remaining Burst Time |
---|---|---|---|---|---|---|---|
9-13ms | P4, P5 | P3 | |||||
P4 | 6ms | 0ms | 5ms | 5ms | |||
P5 | 8ms | 0ms | 2ms | 2ms |
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
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time | Remaining Burst Time |
---|---|---|---|---|---|---|---|
13-15ms | P4 | 6ms | P4 | P5 | 0ms | 5ms | 5ms |
At time = 15,
- After completion of process P5, Process P4 is selected at last and execute till it gets finished
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time | Remaining Burst Time |
---|---|---|---|---|---|---|---|
15-20ms |
At time = 20,
- Process P4 will finish its execution.
- The overall execution of the processes will be as shown below:
Time Instance | Process | Arrival Time | Ready Queue | Running Queue | Execution Time | Initial Burst Time | Remaining Burst Time |
---|---|---|---|---|---|---|---|
0-2ms | P1 | 0ms | P1 | 2ms | 3ms | 1ms | |
2-3ms | P2 | P1 | |||||
P2 | 2ms | 0ms | 6ms | 6ms | |||
3-4ms | P2 | 2ms | P2 | 1ms | 6ms | 5ms | |
4-6ms | P2 | 2ms | P3 | P2 | 2ms | 5ms | 3ms |
P3 | 4ms | 0ms | 4ms | 4ms | |||
6-8ms | P2 | 2ms | P3, P4 | P2 | 2ms | 3ms | 1ms |
P3 | 4ms | 0ms | 4ms | 4ms | |||
P4 | 6ms | 0ms | 5ms | 5ms | |||
8-9ms | P3, P4, P5 | P2 | |||||
P3 | 4ms | 0ms | 4ms | 4ms | |||
P4 | 6ms | 0ms | 5ms | 5ms | |||
P5 | 8ms | 0ms | 2ms | 2ms | |||
9-13ms | P4, P5 | P3 | |||||
P4 | 6ms | 0ms | 5ms | 5ms | |||
P5 | 8ms | 0ms | 2ms | 2ms | |||
13-15ms | P4 | 6ms | P4 | P5 | 0ms | 5ms | 5ms |
15-20ms |
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,
Processes | AT | BT | CT | TAT | WT |
---|---|---|---|---|---|
P1 | 0 | 3 | 3 | 3-0 = 3 | 3-3 = 0 |
P2 | 2 | 6 | 9 | 9-2 = 7 | 7-6 = 1 |
P3 | 4 | 4 | 13 | 13-4 = 9 | 9-4 = 5 |
P4 | 6 | 5 | 20 | 20-6 = 14 | 14-5 = 9 |
P5 | 8 | 2 | 15 | 15-8 = 7 | 7-2 = 5 |
Output:
Total Turn Around Time = 40 ms
So, Average Turn Around Time = 40/5 = 8.00 msAnd, 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 <bits/stdc++.h> 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 <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 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 |
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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