[QE-users] Whether do I need to building my own FFTW3 Interface Wrapper Library or use the integrated one of intel parallel studio for compiling q-e?

[Hongyi Zhao]

On Sat, Jul 18, 2020 at 10:33 AM Hongyi Zhao <hongyi.zhao at gmail.com> wrote:
>
> Hi,
>
> For compiling the q-e git master version, I use the
> parallel_studio_xe/2020.1.102 as the toolchain. I also noted that the
> intel official notes on "Building Your Own FFTW3 Interface Wrapper
> Library" from here:
> https://software.intel.com/content/www/us/en/develop/documentation/mkl-developer-reference-fortran/top/appendix-d-fftw-interface-to-intel-math-kernel-library/fftw3-interface-to-intel-math-kernel-library/building-your-own-fftw3-interface-wrapper-library.html.
>
> I'm not sure whether I must build my own FFTW3 Interface Wrapper
> Library or should I use the precompiled integrated version.

I finally find the following notes on this problem from the
user_guide: https://github.com/QEF/q-e/blob/e240b95c28a8f7dfbc8188c48ac4a290b29ca146/Doc/user_guide.tex#L688.
It told the following:


\item \texttt{-D\_\_DFTI} for DFTI (Intel MKL library),
[...]
If you have MKL libraries, you may either use the provided FFTW3
interface (v.10 and later), or directly link FFTW3 from MKL (v.12
and later) or use DFTI (recommended).


So, it seems integrated version in MKL will be used by default, if
possiable. And I also noted the following line in my make.inc file,
which should confirm the above point of view, after the configure
command has finished successfully:

DFLAGS         =  -D__DFTI -D__MPI -D__SCALAPACK -Duse_beef

If I'm wrong, please correct me.
-- 
Hongyi Zhao <hongyi.zhao at gmail.com>