OpenMP
krisrak
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Hello OpenMP
The sections below shows how to write a simple OpenMP program.
Include Header File
OpenMP program will have to include the omp.h header file
#include <omp.h>
OpenMP Offload
#pragma omp target map(from:is_cpu) map(tofrom:data[0:N])
Loop Parallelism
#pragma omp parallel for
Hands-on Demo
The OpenMP example shown on the right will allocate memory for an array which is initialized to some values, next the task of doubling the array values is offloaded to a device and then finally the result is printed out on the host.
Input array is inialized to:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Expected output after computation on device:
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
hello.cpp
Compiling OpenMP code
To compile a OpenMP program, initialize environment variables and then use icpx to compile as shown below:
source /opt/intel/inteloneapi/setvars.sh
icpx -fiopenmp -fopenmp-targets=spir64 hello.cpp
Check OpenMP Compiler Version
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#include <omp.h>
#include <iostream>
static const int N = 16;
int main(){
int is_cpu = true;
int *data = static_cast<int*>(malloc(N * sizeof(int)));
for(int i=0; i<N; i++) data[i] = i;
#pragma omp target map(from:is_cpu) map(tofrom:data[0:N])
{
is_cpu=omp_is_initial_device();
#pragma omp parallel for
for (int i=0; i<N; i++)
data[i] *= 2;
}
printf ("Running on %s\n", (is_cpu?"CPU":"GPU"));
for(int i=0; i<N; i++) std::cout << data[i] << std::endl;
free(data);
return 0;
}
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