lammps/src/GPU/pair_lj_expand_gpu.cpp

/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   https://www.lammps.org/, Sandia National Laboratories
   LAMMPS development team: developers@lammps.org

   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 author: Inderaj Bains (NVIDIA), ibains@nvidia.com
------------------------------------------------------------------------- */

#include "pair_lj_expand_gpu.h"

#include "atom.h"
#include "domain.h"
#include "error.h"
#include "force.h"
#include "gpu_extra.h"
#include "neigh_list.h"
#include "neighbor.h"
#include "suffix.h"

#include <cmath>

using namespace LAMMPS_NS;

// External functions from cuda library for atom decomposition

int lje_gpu_init(const int ntypes, double **cutsq, double **host_lj1, double **host_lj2,
                 double **host_lj3, double **host_lj4, double **offset, double **shift,
                 double *special_lj, const int nlocal, const int nall, const int max_nbors,
                 const int maxspecial, const double cell_size, int &gpu_mode, FILE *screen);
void lje_gpu_reinit(const int ntypes, double **cutsq, double **host_lj1, double **host_lj2,
                    double **host_lj3, double **host_lj4, double **offset, double **shift);
void lje_gpu_clear();
int **lje_gpu_compute_n(const int ago, const int inum, const int nall, double **host_x,
                        int *host_type, double *sublo, double *subhi, tagint *tag, int **nspecial,
                        tagint **special, const bool eflag, const bool vflag, const bool eatom,
                        const bool vatom, int &host_start, int **ilist, int **jnum,
                        const double cpu_time, bool &success);
void lje_gpu_compute(const int ago, const int inum, const int nall, double **host_x, int *host_type,
                     int *ilist, int *numj, int **firstneigh, const bool eflag, const bool vflag,
                     const bool eatom, const bool vatom, int &host_start, const double cpu_time,
                     bool &success);
double lje_gpu_bytes();

/* ---------------------------------------------------------------------- */

PairLJExpandGPU::PairLJExpandGPU(LAMMPS *lmp) : PairLJExpand(lmp), gpu_mode(GPU_FORCE)
{
  respa_enable = 0;
  cpu_time = 0.0;
  suffix_flag |= Suffix::GPU;
  GPU_EXTRA::gpu_ready(lmp->modify, lmp->error);
}

/* ----------------------------------------------------------------------
   free all arrays
------------------------------------------------------------------------- */

PairLJExpandGPU::~PairLJExpandGPU()
{
  lje_gpu_clear();
}

/* ---------------------------------------------------------------------- */

void PairLJExpandGPU::compute(int eflag, int vflag)
{
  ev_init(eflag, vflag);

  int nall = atom->nlocal + atom->nghost;
  int inum, host_start;

  bool success = true;
  int *ilist, *numneigh, **firstneigh;
  if (gpu_mode != GPU_FORCE) {
    double sublo[3], subhi[3];
    if (domain->triclinic == 0) {
      sublo[0] = domain->sublo[0];
      sublo[1] = domain->sublo[1];
      sublo[2] = domain->sublo[2];
      subhi[0] = domain->subhi[0];
      subhi[1] = domain->subhi[1];
      subhi[2] = domain->subhi[2];
    } else {
      domain->bbox(domain->sublo_lamda, domain->subhi_lamda, sublo, subhi);
    }
    inum = atom->nlocal;
    firstneigh =
        lje_gpu_compute_n(neighbor->ago, inum, nall, atom->x, atom->type, sublo, subhi, atom->tag,
                          atom->nspecial, atom->special, eflag, vflag, eflag_atom, vflag_atom,
                          host_start, &ilist, &numneigh, cpu_time, success);
  } else {
    inum = list->inum;
    ilist = list->ilist;
    numneigh = list->numneigh;
    firstneigh = list->firstneigh;
    lje_gpu_compute(neighbor->ago, inum, nall, atom->x, atom->type, ilist, numneigh, firstneigh,
                    eflag, vflag, eflag_atom, vflag_atom, host_start, cpu_time, success);
  }
  if (!success) error->one(FLERR, "Insufficient memory on accelerator");

  if (atom->molecular != Atom::ATOMIC && neighbor->ago == 0)
    neighbor->build_topology();
  if (host_start < inum) {
    cpu_time = platform::walltime();
    cpu_compute(host_start, inum, eflag, vflag, ilist, numneigh, firstneigh);
    cpu_time = platform::walltime() - cpu_time;
  }
}

/* ----------------------------------------------------------------------
   init specific to this pair style
------------------------------------------------------------------------- */

void PairLJExpandGPU::init_style()
{

  // Repeat cutsq calculation because done after call to init_style
  double maxcut = -1.0;
  double cut;
  for (int i = 1; i <= atom->ntypes; i++) {
    for (int j = i; j <= atom->ntypes; j++) {
      if (setflag[i][j] != 0 || (setflag[i][i] != 0 && setflag[j][j] != 0)) {
        cut = init_one(i, j);
        cut *= cut;
        if (cut > maxcut) maxcut = cut;
        cutsq[i][j] = cutsq[j][i] = cut;
      } else
        cutsq[i][j] = cutsq[j][i] = 0.0;
    }
  }
  double cell_size = sqrt(maxcut) + neighbor->skin;

  int maxspecial = 0;
  if (atom->molecular != Atom::ATOMIC) maxspecial = atom->maxspecial;
  int mnf = 5e-2 * neighbor->oneatom;
  int success = lje_gpu_init(atom->ntypes + 1, cutsq, lj1, lj2, lj3, lj4, offset, shift,
                             force->special_lj, atom->nlocal, atom->nlocal + atom->nghost, mnf,
                             maxspecial, cell_size, gpu_mode, screen);
  GPU_EXTRA::check_flag(success, error, world);

  if (gpu_mode == GPU_FORCE) neighbor->add_request(this, NeighConst::REQ_FULL);
}

/* ---------------------------------------------------------------------- */

void PairLJExpandGPU::reinit()
{
  Pair::reinit();

  lje_gpu_reinit(atom->ntypes + 1, cutsq, lj1, lj2, lj3, lj4, offset, shift);
}

/* ---------------------------------------------------------------------- */

double PairLJExpandGPU::memory_usage()
{
  double bytes = Pair::memory_usage();
  return bytes + lje_gpu_bytes();
}

/* ---------------------------------------------------------------------- */

void PairLJExpandGPU::cpu_compute(int start, int inum, int eflag, int /* vflag */, int *ilist,
                                  int *numneigh, int **firstneigh)
{
  int i, j, ii, jj, jnum, itype, jtype;
  double xtmp, ytmp, ztmp, delx, dely, delz, evdwl, fpair;
  double rsq, r2inv, r6inv, forcelj, factor_lj;
  double r, rshift, rshiftsq;
  int *jlist;

  double **x = atom->x;
  double **f = atom->f;
  int *type = atom->type;
  double *special_lj = force->special_lj;

  // loop over neighbors of my atoms

  for (ii = start; ii < inum; ii++) {
    i = ilist[ii];
    xtmp = x[i][0];
    ytmp = x[i][1];
    ztmp = x[i][2];
    itype = type[i];
    jlist = firstneigh[i];
    jnum = numneigh[i];

    for (jj = 0; jj < jnum; jj++) {
      j = jlist[jj];
      factor_lj = special_lj[sbmask(j)];
      j &= NEIGHMASK;

      delx = xtmp - x[j][0];
      dely = ytmp - x[j][1];
      delz = ztmp - x[j][2];
      rsq = delx * delx + dely * dely + delz * delz;
      jtype = type[j];

      if (rsq < cutsq[itype][jtype]) {
        r = sqrt(rsq);
        rshift = r - shift[itype][jtype];
        rshiftsq = rshift * rshift;
        r2inv = 1.0 / rshiftsq;
        r6inv = r2inv * r2inv * r2inv;
        forcelj = r6inv * (lj1[itype][jtype] * r6inv - lj2[itype][jtype]);
        fpair = factor_lj * forcelj / rshift / r;

        f[i][0] += delx * fpair;
        f[i][1] += dely * fpair;
        f[i][2] += delz * fpair;

        if (eflag) {
          evdwl = r6inv * (lj3[itype][jtype] * r6inv - lj4[itype][jtype]) - offset[itype][jtype];
          evdwl *= factor_lj;
        }

        if (evflag) ev_tally_full(i, evdwl, 0.0, fpair, delx, dely, delz);
      }
    }
  }
}