/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   http://lammps.sandia.gov, Sandia National Laboratories
   Steve Plimpton, sjplimp@sandia.gov

   Copyright (2003) Sandia Corporation.  Under the terms of Contract
   DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
   certain rights in this software.  This software is distributed under 
   the GNU General Public License.

   See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */

/* ----------------------------------------------------------------------
   Contributing authors: Mike Brown (ORNL), brownw@ornl.gov
                         Peng Wang (Nvidia), penwang@nvidia.com
                         Inderaj Bains (NVIDIA), ibains@nvidia.com
                         Paul Crozier (SNL), pscrozi@sandia.gov
------------------------------------------------------------------------- */

                          GENERAL NOTES
                          
This library, libgpu.a, provides routines for GPU acceleration
of LAMMPS pair styles. Compilation of this library requires 
installing the CUDA GPU driver and CUDA toolkit for your operating 
system. In addition to the LAMMPS library, the binary nvc_get_devices 
will also be built. This can be used to query the names and 
properties of GPU devices on your system. A Makefile for OpenCL 
compilation is provided, but support for OpenCL use is not currently
provided by the developers.

NOTE: Installation of the CUDA SDK is not required.

Current pair styles supporting GPU acceleration:

  1. lj/cut/gpu
  2. lj/cut/coul/cut/gpu
  3. lj/cut/coul/long/gpu
  4. lj96/cut/gpu
  5. gayberne/gpu
  6. cmm/cg/gpu
  7. cmm/cg/coul/long/gpu

                     MULTIPLE LAMMPS PROCESSES
                     
Multiple LAMMPS MPI processes can share GPUs on the system, but multiple
GPUs cannot be utilized by a single MPI process. In many cases, the
best performance will be obtained by running as many MPI processes as
CPU cores available with the condition that the number of MPI processes
is an integer multiple of the number of GPUs being used. See the 
LAMMPS user manual for details on running with GPU acceleration.

                    BUILDING AND PRECISION MODES

To build, edit the CUDA_ARCH, CUDA_PRECISION, CUDA_HOME, NVCC, CUDA_INCLUD,
CUDA_LIB and CUDA_OPTS variables in one of the Makefiles. CUDA_ARCH should
be set based on the compute capability of your GPU. This can be verified by
running the nvc_get_devices executable after the build is complete.
Additionally, the GPU package must be installed and compiled for LAMMPS.
This may require editing the gpu_SYSPATH variable in the LAMMPS makefile.

Please note that the GPU library accesses the CUDA driver library directly,
so it needs to be linked not only to the CUDA runtime library (libcudart.so)
that ships with the CUDA toolkit, but also with the CUDA driver library
(libcuda.so) that ships with the Nvidia driver. If you are compiling LAMMPS
on the head node of a GPU cluster, this library may not be installed,
so you may need to copy it over from one of the compute nodes (best into
this directory).

The gpu library supports 3 precision modes as determined by 
the CUDA_PRECISION variable:

  CUDA_PREC = -D_SINGLE_SINGLE  # Single precision for all calculations
  CUDA_PREC = -D_DOUBLE_DOUBLE  # Double precision for all calculations
  CUDA_PREC = -D_SINGLE_DOUBLE  # Accumulation of forces, etc. in double

NOTE: Double precision is only supported on certain GPUs (with
      compute capability>=1.3).
      
NOTE: For Tesla and other graphics cards with compute capability>=1.3,
      make sure that -arch=sm_13 is set on the CUDA_ARCH line.

NOTE: For Fermi, make sure that -arch=sm_20 is set on the CUDA_ARCH line.

NOTE: The gayberne/gpu pair style will only be installed if the ASPHERE
      package has been installed before installing the GPU package in LAMMPS.

NOTE: The cg/cmm/gpu and cg/cmm/coul/long/gpu pair styles will only be
      installed if the USER-CG-CMM package has been installed before
      installing the GPU package in LAMMPS.

NOTE: The lj/cut/coul/long/gpu and cg/cmm/coul/long/gpu style will only be 
      installed if the KSPACE package has been installed before installing
      the GPU package in LAMMPS.

                      EXAMPLE BUILD PROCESS
                    
cd ~/lammps/lib/gpu
emacs Makefile.linux
make -f Makefile.linux
./nvc_get_devices
cd ../../src
emacs ./MAKE/Makefile.linux
make yes-asphere
make yes-kspace
make yes-gpu
make linux

------------------------------------------------------------------------
Last merge with gpulammps: r561 on 2010-11-12
------------------------------------------------------------------------
