Assignment 2

Reference Document: A 2.pdf

Q1

Write an OpenMP program that should create 8 threads to run in parallel and display thread id of each created thread.

#include <iostream>
#include <omp.h>
 
using namespace std;
 
int main() {
	#pragma omp parallel num_threads(8)
	cout << omp_get_thread_num();
	return 0;
}

Q2

#include <iostream>
#include <omp.h>
 
using namespace std;
 
int main() {
	int nums[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
	omp_set_num_threads(3);
 
	#pragma omp parallel for schedule(static, 3)
	for (int j = 0; j < 10; j++) {
		nums[j] *= (j+3);
		int x = omp_get_thread_num();
		cout << "At thread: " << x << " iteration: ";
		cout << j << endl;
	}
	for (int i = 0; i < 10; i++) {
		cout << nums[i] << " ";
	}
	cout << endl;
	return 0;
}

Output

At thread: 0 iteration 0
At thread: 0 iteration 1
At thread: 0 iteration 2
At thread: 1 iteration 3
At thread: 1 iteration 4
At thread: 1 iteration 5
At thread: 2 iteration 6
At thread: 2 iteration 7
At thread: 2 iteration 8
At thread: 0 iteration 9

3 8 15 24 35 48 63 80 99 120

Q3

Can you describe the use of the following terms or clauses in OpenMP:

a) lastprivate(var)

The lastprivate(var)​ clause in OpenMP is used to tell the compiler to copy the result of the last thread that will be working on the variable var​ to the same global or overall system variable

b) schedule(static, 4)

The schedule(static, 4)​ clause is used by OpenMP to dictate the order in which iterations are split and assigned to the threads. According to this static​ clause, the iterations should be split into chunks of size 4​. These chunks are then further assigned to the threads for processing in a round robin fashion.

Q4

Calculate the total communication cost required to transfer 400 mbits of data from Sender to Receiver3. Bandwidth of the link is 10 mbits/s.

Communication Architecture
​​

Store and forward routing

$$\text{Cost}=t_s+n{t}_h+mn{t}_w$$ $$\text{Cost}=1+(3)(5)+(400)(3)(\frac{1}{10})$$

Packet routing

$$\text{Cost}=t_s+n{t}_h+m{t}_w$$ $$\text{Cost}=1+(3)(5)+(400)(\frac{1}{10})$$

Cut through routing: t_w = 0.01

Since $t_w$ = $0.01$ then Bandwidth = $100$ mbits/s

$$\text{Cost}=t_s+n{t}_h+m{t}_w$$ $$\text{Cost}=1+(3)(5)+(400)(\frac{1}{100})$$

Simplified cost model: t_h = 0 and t_w = 0.01

$$\text{Cost}=t_s+m{t}_w$$ $$\text{Cost}=1+(400)(\frac{1}{100})$$