Difference between revisions of "How to Use OpenMP"
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| − | This will give you a general overview of how to compile and execute a program that has been [[Parallel_Programming|parallelized]] with [[ | + | This will give you a general overview of how to compile and execute a program that has been [[Parallel_Programming|parallelized]] with [[OpenMP]]. |
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For example: if you plan to use an Intel compiler for your OpenMP code written in C, you have to type this to create an application called "omp_code.exe": | For example: if you plan to use an Intel compiler for your OpenMP code written in C, you have to type this to create an application called "omp_code.exe": | ||
$ icc -fopenmp omp_code.c -o omp_code.exe | $ icc -fopenmp omp_code.c -o omp_code.exe | ||
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| + | == How to Run an OpenMP Application == | ||
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| + | === Setting OMP_NUM_THREADS === | ||
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| + | If you forget to set OMP_NUM_THREADS to any value, the default value of your cluster environment will be used. In most cases, the default is 1, so that your program is executed serially. | ||
| + | |||
| + | One way to specify the number of threads | ||
Revision as of 16:05, 4 April 2018
Basics
This will give you a general overview of how to compile and execute a program that has been parallelized with OpenMP.
How to Compile OpenMP Code
As opposed to MPI, you do not have to load any modules to use OpenMP, but set an additional compiler flags to tell the compiler to enable OpenMP. Otherwise, the OpenMP pragmas in the code will be ignored by the compiler.
Depending on which compiler you have loaded, use one of the flags below to compile your code.
| Compiler | Flag |
| GNU | -fopenmp |
| Intel | -openmp |
| Oracle | -xopenmp |
For example: if you plan to use an Intel compiler for your OpenMP code written in C, you have to type this to create an application called "omp_code.exe":
$ icc -fopenmp omp_code.c -o omp_code.exe
How to Run an OpenMP Application
Setting OMP_NUM_THREADS
If you forget to set OMP_NUM_THREADS to any value, the default value of your cluster environment will be used. In most cases, the default is 1, so that your program is executed serially.
One way to specify the number of threads