omp

The results look suspicious to me… But I wrote down this note many days ago 🦥. Maybe I need to evaluate it again. Multiple Parallel Regions The cost of constructing parallel region is expensive in OpenMP. Let’s use two example for illustration: Three loops operating on a vector of size 2^31, e.g., for(size_t i = 0; i < vec.size(); i++) vec[i] += 1, vec[i] *= 0.9, vec[i] /= 7, Case 1: a large parallel region including the three loops by omp parallel { omp for }...

One of my old-day notes 🦥. Collapse of Nested Loops The collapse clause converts a prefect nested loop into a single loop then parallelize it. The condition of a perfect nested loop is that, the inner loop is tightly included by the outer loop, and no other codes lying between: for(int i = 0 ... ) { for(int j = 0 ...) { task[i][j]; } } Such condition is hard to meet....