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[ESPResSo-devel] CUDA


From: Axel Arnold
Subject: [ESPResSo-devel] CUDA
Date: Mon, 16 Sep 2013 18:28:33 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130801 Thunderbird/17.0.8

Hi all,

since the CUDA part was somewhat messed up, here some background on CUDA/MPI.

MPI code is compiled by a compiler wrapper, typically mpicc or so. CUDA code in turn is compiled using nvcc, which for the host part is a wrapper around gcc. On many systems, that will be a slightly older gcc version than the default compiler. The header fiel cuda.h is targeted at this older gcc and therefore might simply not work with the default gcc. Therefore, mpicc and nvcc should be regarded as incompatible.

The solution is to split the CUDA and MPI code, so that they can be compiled by separate compilers. That are the .cpp and _cuda.cu files. However, equally important is to keep the header files clean of MPI/CUDA related things. For historic reasons, most ESPResSo headers do include mpi.h. Therefore, CUDA code should usually NOT include other ESPResSo headers if these were not checked to be MPI-free. On the other hand, the headers should NOT contain any #include <cuda.h> if they are included outside .cu-files. Usually, you don't need such headers, with exception of cuda_utils.hpp, which is a CUDA helper file and only meant to be included in .cu-files.

As a rule of thumb, a CUDA-accelerated algorithm now has three files: algo.cpp for the MPI-related implementation. algo_cuda.cpp for the CUDA-related implementation and algo.hpp which is both CUDA- and MPI-free, and just declares exported functions and maybe common data types.

Cheers,
Axel

--
JP Dr. Axel Arnold
ICP, Universit├Ąt Stuttgart
Allmandring 3
70569 Stuttgart, Germany
Email: address@hidden
Tel: +49 711 685 67609




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