PGI Fortran Reference manual - The Portland Group

OpenMP Directives for Fortran8.9.3. OMP_NESTEDOMP_NESTED currently has no effect. Typically this variable enables (TRUE) or disables(FALSE) nested parallelism.8.9.4. OMP_NUM_THREADSOMP_NUM_THREADS specifies the number of threads to use during execution of parallel regions.The default value for this variable is 1. For historical reasons, the environment variable NCPUS issupported with the same functionality. In the event that both OMP_NUM_THREADS and NCPUSare defined, the value of OMP_NUM_THREADS takes precedence.OMP_NUM_THREADS defines the threads that are used to execute the program, regardless of thenumber of physical processors available in the system. As a result, you can run programs using morethreads than physical processors and they execute correctly. However, performance of programs executedin this manner can be unpredictable, and oftentimes will be inefficient.8.9.5. OMP_PROC_BINDOMP_PROC_BIND specifies whether executing threads should be bound to a core duringexecution. Allowable values are "true" and "false".8.9.6. OMP_SCHEDULEOMP_SCHEDULE specifies the type of iteration scheduling to use for DO and PARALLEL DOloop directives that include the SCHEDULE(RUNTIME) clause, described in SCHEDULE. Thedefault value for this variable is STATIC.If the optional chunk size is not set, a chunk size of 1 is assumed except in the case of a staticschedule. For a static schedule, the default is as defined in DO...END DO.Examples of the use of OMP_SCHEDULE are as follows:% setenv OMP_SCHEDULE "STATIC, 5"% setenv OMP_SCHEDULE "GUIDED, 8"% setenv OMP_SCHEDULE "DYNAMIC"8.9.7. OMP_STACKSIZEOMP_STACKSIZE is an OpenMP 3.0 feature that controls the size of the stack for newly-createdthreads. This variable overrides the default stack size for a newly created thread. The valueis a decimal integer followed by an optional letter B, K, M, or G, to specify bytes, kilobytes,megabytes, and gigabytes, respectively. If no letter is used, the default is kilobytes. There is nospace between the value and the letter; for example, one megabyte is specified 1M. The followingexample specifies a stack size of 8 megabytes.% setenv OMP_STACKSIZE 8MPGI Fortran Reference Guide 185