[QE-developers] DFTI and OpenMP detection in configure

[Lorenzo Paulatto]

We have three things:
1. Intel fourier transform library DFTI
2. Intel fourier transform library with FFTW3-like interface in 
MKLROOT/interfaces/fft3xf
3. Internal FFTW2 or system FFTW3 open-source library

 From what I've see, performance wise
1 is faster 2 is faster than 3

But 1 is not thread safe, hence not compatible with openmp

cheers


On 9/16/19 5:33 PM, Ye Luo wrote:
> I got a bit confused. When you say FFTW, did you it mean the FFTW3 
> library or the internal FFTW shipped with QE?
> 
> DFTI vs FFTW3 on intel platforms
> Intel claimed comparable performance using DFTI and FFTW3 interfaces 
> provided by MKL.
> But QE with DFTI outperforms FFTW3 in both absolute performance and 
> thread salability.
> 
> I never did a comparison between MKL DFT and fftw.org <http://fftw.org> 
> FFTW3 on Intel platforms.
> 
> Best,
> 
> Ye
> ===================
> Ye Luo, Ph.D.
> Computational Science Division & Leadership Computing Facility
> Argonne National Laboratory
> 
> 
> Lorenzo Paulatto <paulatz at gmail.com <mailto:paulatz at gmail.com>> 于2019年 
> 9月16日周一 上午4:18写道：
> 
>     Ok, I answer to myself: using DFTI with openmp causes mysterious
>     problems usually using diagonalization. Do you know if using the Intel
>     FFTW interface would work around these or if it is exactly the same
>     thing? Because, the little bit of scalability that I can gain from
>     openmp is exactly lost by the performance I loose with FFTW3 wrt DFTI...
> 
>     cheers
> 
>     On 16/09/2019 10:30, Lorenzo Paulatto wrote:
>      > Hello,
>      > I have noticed that the configure script detects and enables
>      > automatically the DFTI FFT libraries when executed without any
>     specific
>      > switch, but that it uses FFTW instead when executed with the
>      > --enable-openmp switch.
>      >
>      > I was wondering if this is intentional (i.e. because FFTW can give
>      > better performance with openmp? Or DFTI does not work with
>     openmp?) or
>      > it is a bug.
>      >
>      > cheers
>      >
> 
>     -- 
>     Dr. Lorenzo Paulatto
>     IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
>     phone: +33 (0)1 442 79822 / skype: paulatz
>     <http://www.impmc.upmc.fr/~paulatto/> <http://sf.net/p/d3q>
>     23-24/423 B115, 4 place Jussieu 75252 Paris CX 05
> 
>     -- 
>     Lorenzo Paulatto - Paris
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-- 
Lorenzo Paulatto - Paris