OpenMP more threads drastically increases total time - c++

Question

I am writing a Pi estimator for class. The point is to estimate Pi using OpenMP and to analyze the speedup provided by using three separate schedules, static, dynamic and guided. However my total time skyrockets when I add threads. My total time for 1 thread is around 21 seconds, and for 2 threads is roughly 145 seconds. I can't figure out why. Here is my code:
#include <stdio.h>
#include <time.h>
#include <ctime>
#include <omp.h>
#include <assert.h>
#include <cstdlib>
#include <string>
#include <iostream>
#include <stdlib.h>
using namespace std;
void computePi(int, int);
int main(int argc, char *argv[])
{
cout.precision(20);
omp_set_dynamic(0);
int i, p;
int n;
// loop {number of iterations} [number of threads]
if (argc > 1)
{
n = atoll(argv[1]);
p = atoi(argv[2]);
}
else
{
n = 10000000;
p = 8;
}
printf("Debug: dart throws = %d \n", n);
printf("Debug: number of requested threads = %d\n", p);
omp_set_num_threads(p);
double time = omp_get_wtime();
//dispArray(a,n);
computePi(n, p);
time = omp_get_wtime() - time;
printf("Total time = %f seconds \n ", time);
return 0;
}
void computePi(int n, int p) {
omp_set_num_threads(p);
int i;
int hits = 0;
srand(time(NULL));
double timeStatic = omp_get_wtime();
#pragma omp parallel for shared(i) schedule(static) reduction(+:hits)
for (i = 0; i<n; i++)
{
float r, x, xdiff, y, ydiff;
x = (float)rand() / (float)RAND_MAX;
y = (float)rand() / (float)RAND_MAX;
if (y > .50)
{
ydiff = y - .50;
}
else
{
ydiff = .50 - y;
}
if (x > .50)
{
xdiff = x - .50;
}
else
{
xdiff = .50 - x;
}
xdiff *= xdiff;
ydiff *= ydiff;
r = sqrt(ydiff + xdiff);
if (r <= .50)
{
hits += 1;
}
}
timeStatic = omp_get_wtime() - timeStatic;
float percentage;
percentage = (float)hits / (float)n;
cout << "Static Loop" << endl;
cout << "Hit Percentage: " << percentage * 100 << "%" << endl;
cout << "Pi Estimation: " << percentage * 4 << endl;
cout << "Time Taken: " << timeStatic << endl << endl;
hits = 0;
double timeDynamic = omp_get_wtime();
#pragma omp parallel for shared(i) schedule(dynamic) reduction(+:hits)
for (i = 0; i<n; i++)
{
float r, x, xdiff, y, ydiff;
x = (float)rand() / (float)RAND_MAX;
y = (float)rand() / (float)RAND_MAX;
if (y > .50)
{
ydiff = y - .50;
}
else
{
ydiff = .50 - y;
}
if (x > .50)
{
xdiff = x - .50;
}
else
{
xdiff = .50 - x;
}
xdiff *= xdiff;
ydiff *= ydiff;
r = sqrt(ydiff + xdiff);
if (r <= .50)
{
hits += 1;
}
}
timeDynamic = omp_get_wtime() - timeDynamic;
percentage = (float)hits / (float)n;
cout << "Dynamic Loop" << endl;
cout << "Hit Percentage: " << percentage * 100 << "%" << endl;
cout << "Pi Estimation: " << percentage * 4 << endl;
cout << "Time Taken: " << timeDynamic << endl << endl;
hits = 0;
double timeGuided = omp_get_wtime();
#pragma omp parallel for shared(i) schedule(guided) reduction(+:hits)
for (i = 0; i<n; i++)
{
float r, x, xdiff, y, ydiff;
x = (float)rand() / (float)RAND_MAX;
y = (float)rand() / (float)RAND_MAX;
if (y > .50)
{
ydiff = y - .50;
}
else
{
ydiff = .50 - y;
}
if (x > .50)
{
xdiff = x - .50;
}
else
{
xdiff = .50 - x;
}
xdiff *= xdiff;
ydiff *= ydiff;
r = sqrt(ydiff + xdiff);
if (r <= .50)
{
hits += 1;
}
}
timeGuided = omp_get_wtime() - timeGuided;
percentage = (float)hits / (float)n;
cout << "Guided Loop" << endl;
cout << "Hit Percentage: " << percentage * 100 << "%" << endl;
cout << "Pi Estimation: " << percentage * 4 << endl;
cout << "Time Taken: " << timeGuided << endl << endl;
return;
}
Any help would be appreciated.