This simple program benchmarks the 1D real-to-complex Fast Fourier Transform made available by the FFTW library. It performs a direct-inverse transform cycle on a large 1D array many times over and measures the wallclock time.
It is based on this GitHub Gist.
First define the FFTWF_LIB environment variable, pointing it to the location
of the FFTW library directory. For example, on Fugaku I set
export FFTWF_LIB="-L/vol0004/apps/oss/spack-v0.16/opt/spack/linux-rhel8-a64fx/fj-4.3.1/fujitsu-fftw-master-2irjm2a56j7tahcmggbnde2uxf6gjdml/lib -Wl,-rpath,/vol0004/apps/oss/spack-v0.16/opt/spack/linux-rhel8-a64fx/fj-4.3.1/fujitsu-fftw-master-2irjm2a56j7tahcmggbnde2uxf6gjdml/lib -lfftw3f"
which uses the fujitsu-fftw Spack module.
Also if you don't want to use the Fujitsu compiler you must also set the
FORTCOMP environment variable to your compiler of choice, set the
FORTOPT environment variable with your optimisation flags and set the
export FORTLIB=" " (note the space).