The compiler offers you two methods of implementing shared memory program parallelization. Program parallelization using pragma directives compliant to the OpenMP Application Program Interface specification. All methods of program parallelization are enabled when the -qsmp compiler option is in effect without the omp suboption. Parallel regions of program code are executed by multiple threads, possibly running on multiple processors. The number of threads created is determined by the run-time options and calls to library functions.
Work is distributed among available threads according to the specified scheduling algorithm.
IBM directives exploit shared memory parallelism through the parallelization of countable loops . A loop is considered to be countable if it has any of the forms described in Countable Loops . The compiler can automatically locate and where possible parallelize all countable loops in your program code. The compiler must be invoked using a thread-safe compiler mode. You can also explicitly instruct the compiler to parallelize selected countable loops.