OpenMP Environment Variables

This topic describes the standard OpenMP environment variables (with the OMP_ prefix) and Intel-specific environment variables (with the KMP_ prefix) that are Intel extensions to the standard Fortran Compiler .

Standard Environment Variables

Variable

Description

Default

OMP_SCHEDULE

Sets the run-time schedule type and chunk size.

static, no chunk size specified

OMP_NUM_THREADS

Sets the number of threads to use during execution.

Number of processors

OMP_DYNAMIC

Enables (true) or disables (false) the dynamic adjustment of the number of threads.

false

OMP_NESTED

Enables (true) or disables (false)nested parallelism.

false

Intel Extension Environment Variables

Environment Variable

Description

Default

KMP_LIBRARY

Selects the OpenMP runtime library throughput. The options for the variable value are: serial, turnaround, or throughput indicating the execution mode. The default value of throughput is used if this variable is not specified.

throughput
(execution mode)

KMP_STACKSIZE

Sets the number of bytes to allocate for each parallel thread to use as its private stack. Use the optional suffix b, k, m, g, or t, to specify bytes, kilobytes, megabytes, gigabytes, or terabytes.

IA-32: 2m

Itanium compiler: 4m