我有下面的代碼的問題:平行與OMP stucks
int *chosen_pts = new int[k];
std::pair<float, int> *dist2 = new std::pair<float, int>[x.n];
// initialize dist2
for (int i = 0; i < x.n; ++i) {
dist2[i].first = std::numeric_limits<float>::max();
dist2[i].second = i;
}
// choose the first point randomly
int ndx = 1;
chosen_pts[ndx - 1] = rand() % x.n;
double begin, end;
double elapsed_secs;
while (ndx < k) {
float sum_distribution = 0.0;
// look for the point that is furthest from any center
begin = omp_get_wtime();
#pragma omp parallel for reduction(+:sum_distribution)
for (int i = 0; i < x.n; ++i) {
int example = dist2[i].second;
float d2 = 0.0, diff;
for (int j = 0; j < x.d; ++j) {
diff = x(example,j) - x(chosen_pts[ndx - 1],j);
d2 += diff * diff;
}
if (d2 < dist2[i].first) {
dist2[i].first = d2;
}
sum_distribution += dist2[i].first;
}
end = omp_get_wtime() - begin;
std::cout << "center assigning -- "
<< ndx << " of " << k << " = "
<< (float)ndx/k * 100
<< "% is done. Elasped time: "<< (float)end <<"\n";
/**/
bool unique = true;
do {
// choose a random interval according to the new distribution
float r = sum_distribution * (float)rand()/(float)RAND_MAX;
float sum_cdf = dist2[0].first;
int cdf_ndx = 0;
while (sum_cdf < r) {
sum_cdf += dist2[++cdf_ndx].first;
}
chosen_pts[ndx] = cdf_ndx;
for (int i = 0; i < ndx; ++i) {
unique = unique && (chosen_pts[ndx] != chosen_pts[i]);
}
} while (! unique);
++ndx;
}
正如你可以看到我使用OMP for循環使並行。它工作正常,我可以實現顯着的加速。但是,如果我增加x.n
價值超過2000萬的功能停止工作8-10循環後:
- 它doestn產生任何輸出(STD ::法院)
- 只有一個核心工作
- 沒有錯誤,無論如何
如果我註釋掉而循環,它再次按預期工作。所有內核都很忙,每次迭代後都會有輸出,我可以根據需要增加超過1億的k.n
。
謝謝!我本人從未想過自己。浮點運算的問題是未來需要注意的問題。 – user1930254