There are multiple BLAS and LAPACK libraries out there. Most Linux distributions come with pre-compiled BLAS or ATLAS libraries. We strongly discourage you to use those libraries. According to our experience, these libraries are slow. Things have been improved with recent ATLAS development versions, but they have still a hard time to catch up with Intel MKL or GotoBLAS/OpenBLAS implementations.
We found that on Intel platforms, GotoBLAS/OpenBLAS or Intel MKL implementations were the fastest. The advantage of GotoBLAS and OpenBLAS being that they are distributed with a BSD-like license. The choice is yours.
GotoBLAS has been extremely well hand-optimized by Kazushige Goto. The project has been released under a BSD-like license. Unfortunately, it is not maintained anymore (at this time), but several forks have been released later. Our preference goes to OpenBLAS.
We provide below simple instructions to install OpenBLAS.
First get the latest OpenBLAS stable code:
git clone git://github.com/xianyi/OpenBLAS.git
You will need a Fortran compiler. On most Linux distributions,
gfortran is available.
For e.g., on Debian,
apt-get install gfortran
If you prefer, you can also install GCC 4.6 which also supports Fortran language.
On FreeBSD, gfortran is not available, so please use GCC 4.6.
pkg_add -r gcc46
On MacOS X, you should install one gfortran package provided on this GCC webpage.
You can now go into the OpenBlas directory, and just do:
make NO_AFFINITY=1 USE_OPENMP=1
OpenBLAS uses processor affinity to go faster. However, in general, on a
computer shared between several users, this causes processes to fight for
the same CPU. We thus disable it here with the
NO_AFFINITY flag. We
also use the
USE_OPENMP flag, such that OpenBLAS uses OpenMP and not
pthreads. This is important to avoid some confusion in the number of
threads, as Torch7 uses OpenMP. Read OpenBLAS manual for more details.
You can use
FC variables to control the C and Fortran compilers.
On FreeBSD use 'gmake' instead of 'make'. You also have to specify the correct MD5 sum program You will probably want to use the following command line:
gmake NO_AFFINITY=1 USE_OPENMP=1 CC=gcc46 FC=gcc46 MD5SUM='md5 -q'
On MacOS X, you will also have to specify the correct MD5SUM program:
make NO_AFFINITY=1 USE_OPENMP=1 MD5SUM='md5 -q'
Be sure to specify MD5SUM correctly, otherwise OpenBLAS might not compile LAPACK properly.
At the end of the compilation, you might want to do a
make PREFIX=/your_installation_path/ install
to install OpenBLAS at a specific location. You might also want to keep it where you compiled it.
Note that on MacOS X, the generated dynamic (
.dylib) library does not contain LAPACK. Simply remove
the dylib (keeping the archive
.a) such that LAPACK is correctly detected.
Make sure that CMake can find your OpenBLAS library. This can be done with
before starting cmake command line. On some platforms, the
library might also be not found. In this case, add the path to the
gfortran library into
Intel MKL is a closed-source
library sold by Intel. Follow Intel instructions to unpack MKL. Then make
sure the libraries relevant for your system (e.g.
em64t if you are on a
64 bits distribution) are available in your
LD_LIBRARY_PATH. Both BLAS
and LAPACK interfaces are readily included in MKL.
Make sure that CMake can find your libraries. This can be done with something like
export CMAKE_INCLUDE_PATH=/path/to/mkl/include export CMAKE_LIBRARY_PATH=/path/to/mkl/lib/intel64:/path/to/mkl/compiler/lib/intel64 export LD_LIBRARY_PATH=$CMAKE_LIBRARY_PATH:$LD_LIBRARY_PATH
before starting cmake command line.
Of course, you have to adapt
/path/to/mkl/compiler to your installation setup. In the above
case, we also chose the
intel64 libraries, which might not be what you need.
A common mistake is to forgot the path to Intel compiler libraries. CMake will not be able to detect threaded libraries in that case.
As mentioned above, you should make sure CMake can find your libraries. Carefully watch for libraries found (or not found) in the output generated by cmake.
For example, if you see something like:
-- Checking for [openblas - gfortran] -- Library openblas: /Users/ronan/open/lib/libopenblas.dylib -- Library gfortran: BLAS_gfortran_LIBRARY-NOTFOUND
It means CMake found the OpenBLAS library, but could not make it work properly because it did not find the required gfortran library. Make sure that CMake can find all the required libraries through CMAKE_LIBRARY_PATH. If your libraries are present in LD_LIBRARY_PATH, it should be fine too.
The locations to search for are generally as follows.
These are a bit crytic, but look around and find the path that contains libgfortran.so. And, use
before calling cmake to build torch, this makes sure that OpenBLAS will be found.
Note that CMake will try to detect various BLAS/LAPACK libraries. If you have several libraries installed on your computer (say Intel MKL and OpenBLAS), or if you want to avoid all these checks, you might want to select the one you want to use with:
cd torch7/build cmake .. -DWITH_BLAS=open
Valid options for WITH_BLAS are
mkl (Intel MKL),
acml (AMD ACML),
accelerate (Accelerate framework on MacOS X),
framework on MacOS X) or
Note again that the best choices are probably
consistency reasons, CMake will try to find the corresponding LAPACK
package (and does not allow mixing up different BLAS/LAPACK versions).
GotoBLAS/OpenBLAS and MKL are multi-threaded libraries. With MKL, the number of threads can be controlled by
where N is an integer.
Beware that running small problems on a large number of threads reduce performance! Multi-threading should be enable only for large-scale computations.