To run the Intel® compiler in OpenMP mode, invoke the compiler with the -openmp (Linux*) or /Qopenmp (Windows*) option using a command structured similar to the following:
Platform |
Description |
|---|---|
|
Linux |
ifort -openmp input_file |
|
Windows |
ifort /Qopenmp input_file |
Before you run the multithreaded code, you can set the number of desired threads in the OpenMP environment variable, OMP_NUM_THREADS. For more information, see the OpenMP Environment Variablessection. The Intel Extension Routines topic describes the OpenMP extensions to the specification that have been added by Intel to the Intel® compiler.
The -openmp (Linux*) or /Qopenmp (Windows*) option enables the parallelizer to generate multithreaded code based on the OpenMP directives. The code can be executed in parallel on both uniprocessor and multiprocessor systems.
The -openmp (Linux) or /Qopenmp (Windows) option works with both -O0 (Linux) and /Od (Windows), or with any optimization level of -O1, -O2 and -O3. (Linux) or /O1, /O2 and /O3 (Windows). Specifying -O0 (Linux) or /Od (Windows) with the OpenMP option helps to debug OpenMP applications.
When you use the openmp option, the compiler sets the -auto (Linux) or /Qauto (Windows) option, which causes all variables to be allocated on the stack, rather than in local static storage.
The OpenMP directives use the following format:
Example |
|---|
|
<prefix> <directive> [<clause> [[,] <clause> . . .]] |
where the brackets above mean:
<prefix>: the prefix and directive are required
[<clause>]: if a directive uses one clause or more, the clause(s) is required
[,]: commas between the <clause>s are optional.
For fixed form source input, the prefix is !$OMP or C$OMP
For free form source input, the prefix is !$OMP only.
The prefix is followed by the directive name; for example: !$OMP PARALLEL
Since OpenMP directives begin with an exclamation point, the directives are interpreted as comments if you omit the /Qopenmp (-openmp) option.
The OpenMP constructs defining a parallel region have one of the following syntax forms:
Example Syntax |
|---|
|
!$OMP <directive> <structured block of code> !$OMP END <directive> or !$OMP <directive> <structured block of code> or !$OMP <directive> |
where <directive> is the name of a particular OpenMP directive.
The -openmp-report (Linux) or /Qopenmp-report (Windows) option controls the OpenMP* parallelizer's diagnostic levels 0, 1, or 2 as follows:
Windows* |
Linux* |
Description |
|---|---|---|
|
/Qopenmp-report0 |
-openmp-report0 |
No diagnostic information is displayed. |
|
/Qopenmp-report1 |
-openmp-report1 |
Display diagnostics indicating loops, regions, and sections successfully parallelized. |
|
/Qopenmp-report2 |
-openmp-report2 |
Same as specifying 1 plus diagnostics indicating constructs like MASTER, SINGLE, CRITICAL, ORDERED, ATOMIC directives, and so forth are successfully handled. |
For more information about the option behaviors listed above, see the following topic in Compiler Options: