How to use the OpenCL linear solvers
How to use the OpenCL Linear Solvers
Experimental support was added to the Kratos to use modern GPU (or many-core CPUs) basing on the OpenCL programming model.
In order to provide basic linear system solving capabilities, the Kratos uses the ViennaCL library, recently developed at Vienna TU by Ing. Karl Rupp and others. The library, which features a MIT like license, can be currently downloaded from the Kratos SVN.
Compiling the library
The installation of the library requires the presence of an OpenCL compiler on the system, and of driver support to run on GPUs. If no GPU is present, a fallback on the CPU is provided by the AMD stream implementation.
In order to install the driver (under ubuntu linux 10.04) follow the following steps:
- Download and install the deb package (X86 or x86_64 depending on your system) from the link
 , Post by "Nou". Install both "ati-opencl-runtime" and "ati-opencl-dev"
- If you have a ATI high-end GPU, that you would like to use to accelerate the calculations, make sure you install the catalyst driver 10.4 or later versions
- In order to use NVIDIA GPUs install the driver version 195 or later
In Ubuntu 10.04, you can get a recent enough driver from the repository by typing in the console
sudo apt-get install nvidia-current
You will also need the developer version of the drivers, obtained by
sudo apt-get install nvidia-current-dev
Otherwise, the drivers can be downloaded from http://developer.nvidia.com/object/cuda_3_0_downloads.html#Linux
Warning. Please, note that:
Until we figure out the best way to point the compiler to the OpenCL include folder, this has to be done manually for each computer. For NVidia GPUs, edit the Jamfile in /home/.../kratos/applications/OpenCLapplication from
requirements <include>. <include>custom_external_libraries <define>KRATOS_PYTHON ##<define>VIENNACL_EXPERIMENTAL_DOUBLE_PRECISION_WITH_STREAM_SDK <link>shared
requirements <include>. <include>custom_external_libraries <include>/usr/include/nvidia-current/ <define>KRATOS_PYTHON ##<define>VIENNACL_EXPERIMENTAL_DOUBLE_PRECISION_WITH_STREAM_SDK <link>shared
For ATI GPUs, modify the include block to point to the folder containing your CL folder.
Once you have the required drivers, the compilation of the library has to be done manually by doing
cd applications/OpenCLapplication bjam threading=multi -a
please note that for the moment it can only be compiled with gcc as due to a bug the ATI stream SDK does not work together with the intel compiler
Using the library
The interface to the iterative solver library is very similar to the standard one for the Kratos internal linear solvers:
for example a call to the BICGStabSolver the standard python interface is
linear_solver = BICGSTABSolver(1e-3, 5000)
can be replaced by
from KratosOpenCLApplication import * ##choice of the solver's settings precision = OpenCLPrecision.Single solver_type = OpenCLSolverType.BiCGStab preconditioner_type = OpenCLPreconditionerType.NoPreconditioner ##creating the solver linear_solver = ViennaCLSolver(1e-3,5000,precision,solver_type,preconditioner_type)
the list of options that are currently available is:
OpenCLPrecision.Single //to use single precision in the solution (available in most gpus) OpenCLPrecision.Double //requires hardware support
OpenCLSolverType.CG OpenCLSolverType.BiCGStab OpenCLSolverType.GMRES