fft_test.cpp

#include <fftw3.h>
#include <chrono>
#include <iostream>
#include <omp.h>
#include <vector>





int main(int argc, char ** argv){

	using namespace std::chrono;
	fftwf_complex *in, *out;

	size_t n1 = 256;
	size_t n2 = 256;
	size_t n3 = 64;	
	size_t tot = n1*n2*n3;

	size_t repeats = 1000;
	in = (fftwf_complex*) fftw_malloc(sizeof(fftwf_complex)*tot);
	out = (fftwf_complex*) fftw_malloc(sizeof(fftwf_complex)*tot);

	const int n[2] = {n1,n2};
	

	auto start1 = system_clock::now();
	
	for (size_t i = 0; i < repeats; i++){
		auto p_standard = fftwf_plan_dft_2d(n1,n2,in,out,FFTW_FORWARD,FFTW_ESTIMATE);
#pragma omp parallel for 
		for (size_t k = 0; k < n3; k++){
			fftwf_execute_dft(p_standard,in+n1*n2*k,out+n1*n2*k);
		}
	}
	auto end1 = system_clock::now();

	std::cout << "OMP loop (warmup): " << duration_cast<milliseconds>(end1-start1).count() << std::endl;


	start1 = system_clock::now();
	
	for (size_t i = 0; i < repeats; i++){
		auto p_standard = fftwf_plan_dft_2d(n1,n2,in,out,FFTW_FORWARD,FFTW_ESTIMATE);
#pragma omp parallel for 
		for (size_t k = 0; k < n3; k++){
			fftwf_execute_dft(p_standard,in+n1*n2*k,out+n1*n2*k);
		}
	}
        end1 = system_clock::now();

	std::cout << "OMP loop (second run): " << duration_cast<milliseconds>(end1-start1).count() << std::endl;

	fftwf_init_threads();
	fftwf_plan_with_nthreads(omp_get_max_threads());
	
		
	auto start = system_clock::now();
	for (size_t i = 0; i < repeats; i++) {
	auto p = fftwf_plan_many_dft(2,n,n3,in,n,1,n1*n2,out,n,1,n1*n2,FFTW_FORWARD,FFTW_ESTIMATE);

	fftwf_execute(p);
	}
	auto end = system_clock::now();

	std::cout << "Naive: " << duration_cast<milliseconds>(end-start).count() << std::endl;
	
	start = system_clock::now();
	for (size_t i=0; i < repeats; i++){
		auto p = fftwf_plan_many_dft(2,n,n3,in,n,1,n1*n2,in,n,1,n1*n2,FFTW_FORWARD,FFTW_ESTIMATE);
		fftwf_execute(p);
	}

	end = system_clock::now();
	std::cout << "In place: " << duration_cast<milliseconds>(end-start).count() << std::endl;

	start = system_clock::now();
	for (size_t i = 0; i < repeats; i++){
		auto p = fftwf_plan_many_dft(2,n,n3,in,n,1,n1*n2,out,n,1,n1*n2,FFTW_FORWARD,FFTW_MEASURE);
		fftwf_execute(p);
	}


	end = system_clock::now();
	
	std::cout << "Optimized: " << duration_cast<milliseconds>(end-start).count() << std::endl;


}

Compile with

g++ fft_test.cpp -fopenmp -std=c++11 -lfftw3f -lfftw3_omp -lfftw3f_omp  -lfftw3 -lm -O3