The -par_threshold{n} option sets a threshold for the auto-parallelization of loops based on the probability of profitable execution of the loop in parallel, n=0 to 100. This option is used for loops whose computation work volume cannot be determined at compile-time.
-par_threshold0 - loops get auto-parallelized regardless of computation work volume.
-par_threshold100 - loops get auto-parallelized only if profitable parallel execution is almost certain.
The intermediate 1 to 99 values represent the percentage probability for profitable speedup. For example, n=50 would mean parallelize only if there is a 50% probability of the code speeding up if executed in parallel. Default: n=75.
The compiler applies a heuristic that tries to balance the overhead of creating multiple threads versus the amount of work available to be shared amongst the threads.