Your run-times seem significantly faster than mine are -> mine are closer to 7500 seconds for 0.05 and 128 threads. As for run time measurements, are you using clock() to measure the time? I found when using that it seemed to actually accumulate total run time across all cores, so was not a good measure of overall time. I have been using the double omp_get_wtime() function built into openMP instead, and that gave me values closer to what I expected