[gmx-developers] warning Emulating FMA instructions - this is probably not what you want!

[Szilárd Páll]

On Wed, Oct 17, 2012 at 3:23 PM, Berk Hess <hess at kth.se> wrote:

> Hi,
>
> ICC can actually sometimes be (a lot) faster than gcc on AMD.
> The issue here seems to be that the configuration didn't add a compiler
> flag for fma4.
>

That is only the case on pre-Bulldozer processors like Magny-Cours. On
Bulldozer, with the current kernels gcc is as fast or faster than icc.

--
Szilárd


>
> Cheers,
>
> Berk
>
>
> ----- Reply message -----
> From: "Alexey Shvetsov" <alexxy at omrb.pnpi.spb.ru>
> To: <gmx-developers at gromacs.org>
> Subject: [gmx-developers] warning Emulating FMA instructions - this is
> probably not what you want!
> Date: Wed, Oct 17, 2012 14:00
>
>
> Hi all!
>
> Well ICC isnt good with AMD CPUs especialy with new ones. Try to use
> recent gcc versions like gcc-4.7.
>
>
> Jochen Hub писал 17-10-2012 13:14:
> > Hi developers,
> >
> > does anyone know how to interpret this icc warning:
> >
> > [  8%] /home/jhub/src/gromacs/include/gmx_x86_avx_128_fma.h(88):
> > warning #1224: #warning directive: Emulating FMA instructions - this
> > is probably not what you want!
> >
> >   #warning Emulating FMA instructions - this is probably not what you
> > want!
> >
> > I am compiling 46-release on a Interlagos 6378 with OpenMPI and icc
> > 13.0.0 20120731. My cmake line is:
> >
> > cmake $gmxsrc \
> >     -DFFTW_LIBRARY=$FFTW_LOCATION/lib/libfftw3f.a \
> >     -DFFTW3F_INCLUDE_DIR=$FFTW_LOCATION/include \
> >     -DFFTW3F_LIBRARIES=$FFTW_LOCATION/lib/libfftw3f.a \
> >     -DCMAKE_INSTALL_PREFIX=$(pwd) \
> >     -DGMX_X11=OFF \
> >     -DCMAKE_CXX_COMPILER=$MPICXX \
> >     -DCMAKE_C_COMPILER=$MPICC \
> >     -DGMX_MPI=ON \
> >     -DGMX_PREFER_STATIC_LIBS=ON \
> >     -DGMX_GPU=OFF
> >
> > and cmake reported:
> >
> > -- Performing Test GNU_AVX_CFLAG
> > -- Performing Test GNU_AVX_CFLAG - Success
> > -- Enabling 128-bit AVX Gromacs acceleration (with fused-multiply
> > add), and it will help compiler optimization.
> >
> > Thanks a lot,
> > Jochen
> >
> >
> >
> > --
> > ---------------------------------------------------
> > Dr. Jochen Hub
> > Computational Molecular Biophysics Group
> > Institute for Microbiology and Genetics
> > Georg-August-University of Göttingen
> > Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany.
> > Phone: +49-551-39-14189
> > http://cmb.bio.uni-goettingen.de/
> > ---------------------------------------------------
>
> --
> Best Regards,
> Alexey 'Alexxy' Shvetsov
> Petersburg Nuclear Physics Institute, NRC Kurchatov Institute,
> Gatchina, Russia
> Department of Molecular and Radiation Biophysics
> Gentoo Team Ru
> Gentoo Linux Dev
> mailto:alexxyum at gmail.com
> mailto:alexxy at gentoo.org
> mailto:alexxy at omrb.pnpi.spb.ru
> --
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