FFTW wrapper on MIC

FFTW wrapper on MIC

Hi everyone,

I'm trying to run the MKL fftw wrapper on MIC, but it doesn't work. The code compiles and I can run the binary, but since I don't have the offload report I guess that code don't was really executed on MIC. The code is this:

#include <stdlib.h>
#include <stdio.h>
#include <fftw3.h>

// MAX 480

#define N1 1000
#define N2 1000
#define N3 1000

double getTimeElapsed(struct timeval end, struct timeval start) {
    return (end.tv_sec - start.tv_sec) + (end.tv_usec - start.tv_usec) / 1000000.00;

int compute3DFFT(fftw_complex *dest, fftw_complex *src, int dim1, int dim2, int dim3, int type, unsigned int flags ) {

	if( !dest || !src || dim1<1 || dim2<1 || dim3<1 ) return 0;


	fftw_plan p = fftw_plan_dft_3d(dim1, dim2, dim3, src, dest, type, flags);
	#pragma offload target(mic:0) nocopy(p)

	return 1;


void print(fftw_complex *f, int n){

	int i;
	for(i=0; i<n; i++)
		printf("%d: (%g,%gi)\n", i, f[i][0], f[i][1]);


int main(void) {
	int i;
	fftw_complex *src, *dest;
	double time_elapsed;
	struct timeval start, end;

    	gettimeofday(&start, NULL);


	src = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * N1 * N2 * N3);
	dest = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * N1 * N2 * N3);

	for(i=0; i<N1*N2*N3; i++) {
		src[i][0] = i + 1.0;
		src[i][1] = i + 2.0;

	//print(src, N1*N2*N3);

	compute3DFFT(dest, src, N1, N2, N3, FFTW_FORWARD, FFTW_ESTIMATE);

	print(dest, N1*N2*N3);*/

	fftw_free(src); fftw_free(dest);

	gettimeofday(&end, NULL);
    time_elapsed = getTimeElapsed(end, start);

    printf("Time: %.3f seconds\n", time_elapsed);
	return 0;

I already changed nocopy(p) to in(p) and I get some warnings but the code executed in the same way.

I compiled with this command:

icc -o Xeon fftw_libmic.c -L$MKLROOT/lib/intel64 -lmkl_intel_lp64 -lmkl_core -lmkl_intel_thread -lpthread -lm -openmp -I$MKLROOT/include/fftw  -offload-attribute-target=mic -offload-option,mic,compiler,"  -L$MKLROOT/lib/mic -lmkl_intel_lp64 -lmkl_core -lmkl_intel_thread"

I also make export MKL_MIC_ENABLE=1 and export OFFLOAD_REPORT=2

Like I said, this code runs but only on CPU.

Can you help me ?

Best Regards

4 posts / 0 new
Last post
For more complete information about compiler optimizations, see our Optimization Notice.

I have not tried to do FFTs using offload, but aren't your arrays too big for the Xeon Phi?

If "fftw_complex" is based on "doubles", then your src and dest arrays are each 14.9 GiB.    Even with "float" variables, the two arrays would take 14.9 GiB together.

John D. McCalpin, PhD
"Dr. Bandwidth"
Also, the fftw_plan needs to be created/destroyed in an offload.

#pragma offload target(mic:0) 
fftw_plan p = fftw_plan_dft_3d(dim1, dim2, dim3, src, dest, type, flags);


Thank you both.

I tried the solution of Jeongnim but didn't work.

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