So here's compiling ATLAS on a cluster made up of six dual-socket mobos with 2x quadcore XeonX3480 CPUs and 8 Gb RAM. The cluster is running ROCKS 5.4.3, which is a spin based on Centos 5.6. We then compile GROMACS using ATLAS and compare it with Openblas. Please note that I am not an expert on optimisations (or computers or anything) so comparing Openblas vs ATLAS won't tell you which one is 'better'. They are just numbers based on what someone once observed on a particular system under a particular set of circumstances.
Hurdles: I first had to deal with the lapack + bad symbols + recompile with -fPIC problem (solved by using netlib lapack and building shared libraries), then encountered the 'libgmx.so: undefined reference to _gfortran_' issue (solved by adding -lgfortran to LDFLAGS).
ATLAS
sudo mkdir /share/apps/ATLAS
sudo chown $USER /share/apps/ATLAS
cd ~/tmp
wget http://www.netlib.org/lapack/lapack-3.4.1.tgz
wget http://downloads.sourceforge.net/project/math-atlas/Developer%20%28unstable%29/3.9.72/atlas3.9.72.tar.bz2
tar xvf atlas3.9.72.tar.bz2
cd ATLAS/
mkdir build
cd build
.././configure --prefix=/share/apps/ATLAS -Fa alg '-fPIC' --with-netlib-lapack-tarfile=$HOME/tmp/lapack-3.4.1.tgz --shared
OS configured as Linux (1)make
Assembly configured as GAS_x8664 (2)
Vector ISA Extension configured as SSE3 (6,448)
Architecture configured as Corei1 (25)
Clock rate configured as 3059Mhz
DONE STAGE 5-1-0 at 15:23
ATLAS install complete. Examine
ATLAS/bin/<arch>/INSTALL_LOG/SUMMARY.LOG for details.
ls lib/
libatlas.a libcblas.a libf77blas.a libf77refblas.a liblapack.a libptcblas.a libptf77blas.a libptlapack.a libsatlas.so libtatlas.so libtstatlas.a Makefile Make.inc
make install
In addition to successful copying you'll also get errors along the lines of
cp: cannot stat `/home/me/tmp/ATLAS/build/lib/libsatlas.dylib': No such file or directory
make[1]: [install_lib] Error 1 (ignored)
cp /home/me/tmp/ATLAS/build/lib/libtatlas.dylib /share/apps/ATLAS/lib/.
cp: cannot stat `/home/me/tmp/ATLAS/build/lib/libtatlas.dylib': No such file or directory
make[1]: [install_lib] Error 1 (ignored)
cp /home/me/tmp/ATLAS/build/lib/libsatlas.dll /share/apps/ATLAS/lib/.
cp: cannot stat `/home/me/tmp/ATLAS/build/lib/libsatlas.dll': No such file or directory
make[1]: [install_lib] Error 1 (ignored)
cp /home/me/tmp/ATLAS/build/lib/libtatlas.dll /share/apps/ATLAS/lib/.
cp: cannot stat `/home/me/tmp/ATLAS/build/lib/libtatlas.dll': No such file or directory
make[1]: [install_lib] Error 1 (ignored)
cp /home/me/tmp/ATLAS/build/lib/libsatlas.so /share/apps/ATLAS/lib/.
cp /home/me/tmp/ATLAS/build/lib/libtatlas.so /share/apps/ATLAS/lib/.
because those files don't exist.
Gromacs
FFTW3 was first build according to this. The only difference is the install targets (--prefix) -- I put things in /share/apps/gromacs/.fftwsingle and /share/apps/gromacs/.fftwdouble. Gromacs was downloaded and extracted as shown in that post, and /share/apps/gromacs was created.
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/openmpi/lib:/share/apps/ATLAS/libThe -lgfortran is IMPORTANT, or you'll end up with
#single precision
export LDFLAGS="-L/share/apps/gromacs/.fftwsingle/lib -L/share/apps/ATLAS/lib -latlas -llapack -lf77blas -lcblas -lgfortran"
export CPPFLAGS="-I/share/apps/gromacs/.fftwsingle/include -I/share/apps/ATLAS/include/atlas"
./configure --disable-mpi --enable-float --with-fft=fftw3 --with-external-blas --with-external-lapack --program-suffix=_spa --prefix=/share/apps/gromacs
make -j3
make install
#double precision
make distclean
export LDFLAGS="-L/share/apps/gromacs/.fftwdouble/lib -L/share/apps/ATLAS/lib -latlas -llapack -lf77blas -lcblas -lgfortran"
export CPPFLAGS="-I/share/apps/gromacs/.fftwdouble/include -I/share/apps/ATLAS/include/atlas"
./configure --disable-mpi --disable-float --with-fft=fftw3 --with-external-blas --with-external-lapack --program-suffix=_dpa --prefix=/share/apps/gromacs
make -j3
make install
#single + mpi
make distclean
export LDFLAGS="-L/share/apps/gromacs/.fftwsingle/lib -L/share/apps/ATLAS/lib -latlas -llapack -lf77blas -lcblas -lgfortran"
export CPPFLAGS="-I/share/apps/gromacs/.fftwsingle/include -I/share/apps/ATLAS/include/atlas""
./configure --enable-mpi --enable-float --with-fft=fftw3 --with-external-blas --with-external-lapack --program-suffix=_spampi --prefix=/share/apps/gromacs
make -j3
make install
#double + mpi
make distclean
export LDFLAGS="-L/share/apps/gromacs/.fftwdouble/lib -L/share/apps/ATLAS/lib -latlas -llapack -lf77blas -lcblas -lgfortran"
export CPPFLAGS="-I/share/apps/gromacs/.fftwdouble/include -I/share/apps/ATLAS/include/atlas"
./configure --enable-mpi --disable-float --with-fft=fftw3 --with-external-blas --with-external-lapack --program-suffix=_dpampi --prefix=/share/apps/gromacs
make -j3
make install
libgmx.so: 'undefined reference to _gfortran_' type errors.
Performance
I ran a 6x6x6 nm box of water for 5 million steps (10 ns) to get a rough idea of the performance.
Make sure to put
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/share/apps/ATLAS/libin your ~/.bashrc, and to include it in your SGE jobs files (if that's what you use).
I allocated 8 Gb RAM and 8 cores for each run.
Double precision:
Openblas: 10.560 ns/day (11.7 GFLOPS, runtime 8182 seconds)
ATLAS : 10.544 ns/day (11.6 GFLOPS, runtime 8194 seconds)
Single precision:
Openblas: 17.297 ns/dat (19.1 GFLOPS, runtime 4995 seconds)
ATLAS: 17.351 ns/day (19.2 GFLOPS, runtime 4980 seconds)
That's 15 seconds difference on a 1h 20 min run. I'd say they are identical.
