[gmx-developers] Error configuring 5.0.5 with GMX_BUILD_OWN_FFTW=yes

[Berk Hess]

Hi,

I had a look at my change to the FFTW checks, but I don't see how 
something can go wrong here. As far as I can see the order and essential 
logic have not changed compared to 5.0.4.

Cheers,

Berk

On 05/13/2015 05:54 PM, Mark Abraham wrote:
> Hi,
>
> Thanks for the email.
>
> On Wed, May 13, 2015 at 5:34 PM Hardy, Adam <ah259 at hw.ac.uk 
> <mailto:ah259 at hw.ac.uk>> wrote:
>
>     Dear all,
>
>     I'm having trouble installing the latest release. Leaving all
>     other options default, but switching GMX_BUILD_OWN_FFTW=yes
>     results in a cmake warning:
>
>     "
>     CMake Warning at cmake/gmxManageFFTLibraries.cmake:93 (message):
>        The FFTW library was compiled with neither --enable-sse nor
>     --enable-sse2;
>        those would have enabled SSE(2) SIMD instructions. This will give
>        suboptimal performance.  You should (re)compile the FFTW
>     library with both
>        SSE2 and AVX instruction support (use both --enable-sse2 and
>     --enable-avx).
>        The FFTW library will determine at runtime which SIMD
>     instruction set is
>        fastest for different parts of the FFTs.
>      Call Stack (most recent call first):
>        CMakeLists.txt:742 (include) 
>
>     "
>
> That's inconsistent and somewhat embarassing, but not actually a 
> problem. FFTW hasn't been downloaded or built by the time that warning 
> is issued, so we have some logic that doesn't work correctly in the 
> auto-download case.
>
> Later on, FFTW is built but is still compiled with only --enable-sse2. 
> We may change that behaviour for 5.1, if it is clear that adding 
> --enable-avx as well is always neutral-or-useful, but there's nothing 
> wrong with the resulting mdrun here.
>
>     This configuration works as expected with 5.0.4.
>
>     I get the same results with this setting as "no". This message
>     doesn't make much sense in either case as I do not have an FFTW
>     library on my machine.
>
>
> Hmm that could be a minor problem, but none of us have tried a build 
> on a machine without FFTW, for the obvious reason. :-)
>
>     The error I get in 5.0.4 for this scenario is:
>
>     "
>     Could not find fftw3f library named libfftw3f, please specify its
>     location in CMAKE_PREFIX_PATH or FFTWF_LIBRARY by hand (e.g.
>      -DFFTWF_LIBRARY='/path/to/libfftw3f.so')
>
>      CMake Error at cmake/gmxManageFFTLibraries.cmake:76 (MESSAGE):
>        Cannot find FFTW 3 (with correct precision - libfftw3f for
>     mixed-precision
>        GROMACS or libfftw3 for double-precision GROMACS). Either
>     choose the right
>        precision, choose another FFT(W) library (-DGMX_FFT_LIBRARY),
>     enable the
>        advanced option to let GROMACS build FFTW 3 for you
>        (-GMX_BUILD_OWN_FFTW=ON), or use the really slow GROMACS
>     built-in fftpack
>        library (-DGMX_FFT_LIBRARY=fftpack).
>      Call Stack (most recent call first):
>        CMakeLists.txt:738 (include)
>     "
>
>     I see some in the release notes some changes were made to the
>     cmake warnings for AVX capable processors which I belive mine is 
>
>     (AMD fx-8350).
>
>
> Yes, but we don't expect much/any improvement on AMD cpus from adding 
> --enable-avx. Use --enable-sse2 always (which is what the 
> auto-download does).
>
> Mark
>
>     Thanks,
>
>     Adam Hardy
>     PhD Student
>     School of Engineering and Physical Sciences
>     Heriot-Watt University
>     Edinburgh EH14 4AS, UK
>
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