I am a little confused about creating many_plan by calling fftwf_plan_many_dft_r2c() and executing it with OpenMP. What I am trying to achieve here is to see if explicitly using OpenMP and organizing FFTW data could work together. ( I know I "should" use multithreaded version of fftw but I failed to get a expected speedup from it ).
My code looks like this:
/* I ignore some helper APIs */
#define N 1024*1024 //N is the total size of 1d fft
fftwf_plan p;
float * in;
fftwf_complex *out;
omp_set_num_threads(threadNum); // Suppose threadNum is 2 here
in = fftwf_alloc_real(2*(N/2+1));
std::fill(in,in+2*(N/2+1),1.1f); // just try with a random real floating numbers
out = (fftwf_complex *)&in[0]; // for in-place transformation
/* Problems start from here */
int n[] = {N/threadNum}; // according to the manual, n is the size of each "howmany" transformation
p = fftwf_plan_many_dft_r2c(1, n, threadNum, in, NULL,1 ,1, out, NULL, 1, 1, FFTW_ESTIMATE);
#pragma omp parallel for
for (int i = 0; i < threadNum; i ++)
{
fftwf_execute(p);
// fftwf_execute_dft_r2c(p,in+i*N/threadNum,out+i*N/threadNum);
}
What I got is like this:
If I use fftwf_execute(p), the program executes successfully, but the result seems not correct. ( I compare the result with the version of not using many_plan and openmp )
If I use fftwf_execute_dft_r2c(), I got segmentation fault.
Can somebody help me here? How should I partition the data across multiple threads? Or it is not correct in the first place.
Thank you in advance.
flyree