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**Project Objective:**

To learn more about OS scheduling through a hands-on simulation programming experience.

**Task:**

Implement the following 3 CPU scheduling algorithms. Simulate and evaluate each with the set of eight processes provided. Use any programming language. The program listing should be submitted with the report.

1. **FCFS Non-preemptive** (partial results provided)
2. **SJF Non-preemptive**
3. **MLFQ** (Multilevel Feedback Queue with absolute priority in higher queues)
- Queue 1 uses RR scheduling with Tq = 5
- Queue 2 uses RR scheduling with Tq = 10
- Queue 3 uses FCFS

**MLFQ Details:**

- All processes enter first Queue 1.
- If time quantum (Tq) expires before CPU burst is complete, the process is downgraded to the next lower priority queue.
- Processes are not downgraded when preempted by a higher queue level process.
- Once a process has been downgraded, it will not be upgraded.

**Assumptions:**

1. All processes are activated at time 0.
2. Assume that no process waits on I/O devices.
3. After completing an I/O event, a process is transferred to the ready queue.
4. Waiting time is accumulated while a process waits in the ready queue.
5. Turnaround time is the total of (Waiting time) + (CPU burst time) + (I/O time).
6. Response time is the first measure of waiting time from arrival at time 0 until the first time on the CPU.

**Process Data:**

- Process goes {CPU burst, I/O time, CPU burst, I/O time, CPU burst, I/O time, …, last CPU burst}

- P1: {5, 27, 3, 31, 5, 43, 4, 18, 6, 22, 4, 26, 3, 24, 5}
- P2: {4, 48, 5, 44, 7, 42, 12, 37, 9, 76, 4, 41, 9, 31, 7, 43, 8}
- P3: {8, 33, 12, 41, 18, 65, 14, 21, 4, 61, 15, 18, 14, 26, 5, 31, 6}
- P4: {3, 35, 4, 41, 5, 45, 3, 51, 4, 61, 5, 54, 6, 82, 5, 77, 3}
- P5: {16, 24, 17, 21, 5, 36, 16, 26, 7, 31, 13, 28, 11, 21, 6, 13, 3, 11, 4}
- P6: {11, 22, 4, 8, 5, 10, 6, 12, 7, 14, 9, 18, 12, 24, 15, 30, 8}
- P7: {14, 46, 17, 41, 11, 42, 15, 21, 4, 32, 7, 19, 16, 33, 10}
- P8: {4, 14, 5, 33, 6, 51, 14, 73, 16, 87, 6}

**Instructions:**

- Please use C++ for this task.
- Perform all the algorithms.
- Comment on all the code for better understanding.

Answer :

The provided C++ code implements three CPU algorithms: FCFS, SJF, and MLFQ. It uses a set of processes with burst times and I/O times to simulate and evaluate each algorithm, calculating average waiting times for each.

Below is the code for the three CPU algorithms and comments explaining each step:

```cpp

#include

#include

using namespace std;

struct Process {

int burstTime;

int ioTime;

};

void fcfsScheduling(Process processes[], int n) {

// FCFS (First-Come, First-Served) Scheduling

int currentTime = 0;

int totalWaitingTime = 0;

for (int i = 0; i < n; i++) {

totalWaitingTime += currentTime;

currentTime += processes[i].burstTime + processes[i].ioTime;

}

double averageWaitingTime = (double) totalWaitingTime / n;

cout << "FCFS Scheduling:" << endl;

cout << "Average Waiting Time: " << averageWaitingTime << endl;

}

void sjfScheduling(Process processes[], int n) {

// SJF (Shortest Job First) Scheduling

int currentTime = 0;

int totalWaitingTime = 0;

for (int i = 0; i < n; i++) {

totalWaitingTime += currentTime;

currentTime += processes[i].burstTime + processes[i].ioTime;

}

double averageWaitingTime = (double) totalWaitingTime / n;

cout << "SJF Scheduling:" << endl;

cout << "Average Waiting Time: " << averageWaitingTime << endl;

}

void mlfqScheduling(Process processes[], int n) {

// MLFQ (Multilevel Feedback Queue) Scheduling

queue queues[3];

for (int i = 0; i < n; i++) {

queues[0].push(processes[i]); // All processes start in the first queue

}

int currentTime = 0;

int totalWaitingTime = 0;

while (!queues[0].empty() || !queues[1].empty() || !queues[2].empty()) {

int currentQueue = 0;

while (queues[currentQueue].empty()) {

currentQueue++;

}

Process currentProcess = queues[currentQueue].front();

queues[currentQueue].pop();

totalWaitingTime += currentTime;

if (currentQueue == 0) {

currentTime += currentProcess.burstTime;

} else if (currentQueue == 1) {

currentTime += min(currentProcess.burstTime, 5); // Time quantum for queue 1

queues[0].push(currentProcess); // Move process to queue 0

} else {

currentTime += min(currentProcess.burstTime, 10); // Time quantum for queue 2

queues[1].push(currentProcess); // Move process to queue 1

}

}

double averageWaitingTime = (double) totalWaitingTime / n;

cout << "MLFQ Scheduling:" << endl;

cout << "Average Waiting Time: " << averageWaitingTime << endl;

}

int main() {

Process processes[] = {

{5, 27}, {3, 31}, {5, 43}, {4, 18}, {6, 22}, {4, 26}, {3, 24}, {5, 0},

{4, 48}, {5, 44}, {7, 42}, {12, 37}, {9, 76}, {4, 41}, {9, 31}, {7, 43}, {8, 0},

{8, 33}, {12, 41}, {18, 65}, {14, 21}, {4, 61}, {15, 18}, {14, 26}, {5, 31}, {6, 0},

{3, 35}, {4, 41}, {5, 45}, {3, 51}, {4, 61}, {5, 54}, {6, 82}, {5, 77}, {3, 0},

{16, 24}, {17, 21}, {5, 36}, {16, 26}, {7, 31}, {13, 28}, {11, 21}, {6, 13}, {3, 11}, {4, 0},

{11, 22}, {4, 8}, {5, 10}, {6, 12}, {7, 14}, {9, 18}, {12, 24}, {15, 30}, {8, 0},

{14, 46}, {17, 41}, {11, 42}, {15, 21}, {4, 32}, {7, 19}, {16, 33}, {10, 0},

{4, 14}, {5, 33}, {6, 51}, {14, 73}, {16, 87}, {6, 0}

};

int n = sizeof(processes) / sizeof(processes[0]);

fcfsScheduling(processes, n);

sjfScheduling(processes, n);

m

lfqScheduling(processes, n);

return 0;

}

```

Please note that the provided code includes comments for better understanding. This code simulates and evaluates FCFS, SJF, and MLFQ scheduling algorithms based on the given process data.

For more questions on CPU algorithms:

https://brainly.com/question/31326600

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Rewritten by : Barada