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/*! \internal \file
 *
 * \brief Implements Leap-Frog using CUDA
 *
 * This file contains backend-agnostic code for Leap-Frog integrator class on GPU,
 * including class initialization, and data-structures management.
 *
 * \author Artem Zhmurov <zhmurov@gmail.com>
 *
 * \ingroup module_mdlib
 */
#include "gmxpre.h"

#include "leapfrog_gpu.h"

#include <cassert>
#include <cmath>
#include <cstdio>

#include <algorithm>

#include "gromacs/gpu_utils/devicebuffer.h"
#include "gromacs/math/vec.h"
#include "gromacs/mdlib/leapfrog_gpu_internal.h"
#include "gromacs/mdtypes/group.h"
#include "gromacs/pbcutil/pbc.h"
#include "gromacs/utility/arrayref.h"

namespace gmx
{

void LeapFrogGpu::integrate(DeviceBuffer<Float3>              d_x,
                            DeviceBuffer<Float3>              d_xp,
                            DeviceBuffer<Float3>              d_v,
                            const DeviceBuffer<Float3>        d_f,
                            const float                       dt,
                            const bool                        doTemperatureScaling,
                            gmx::ArrayRef<const t_grp_tcstat> tcstat,
                            const bool                        doParrinelloRahman,
                            const float                       dtPressureCouple,
                            const gmx::Matrix3x3&             prVelocityScalingMatrix)
{
    GMX_ASSERT(numAtoms_ > 0, "The number of atoms needs to be >0.");

    if (doTemperatureScaling)
    {
        GMX_ASSERT(checkDeviceBuffer(d_lambdas_, numTempScaleValues_),
                   "Number of temperature scaling factors changed since it was set for the "
                   "last time.");
        GMX_ASSERT(numTempScaleValues_ == ssize(h_lambdas_),
                   "Number of temperature scaling factors changed since it was set for the "
                   "last time.");

        /* In SYCL, we could use host accessors here, without h_lambdas_.
         * According to a quick test, host accessor is slightly faster when using DPC++ and
         * LevelZero compared to using h_lambdas_ + cgh.copy. But with DPC++ and OpenCL, the host
         * accessor waits for fReadyOnDevice in UpdateConstrainGpu::Impl::integrate. See #4023. */
        for (int i = 0; i < numTempScaleValues_; i++)
        {
            h_lambdas_[i] = tcstat[i].lambda;
        }
        copyToDeviceBuffer(&d_lambdas_,
                           h_lambdas_.data(),
                           0,
                           numTempScaleValues_,
                           deviceStream_,
                           GpuApiCallBehavior::Async,
                           nullptr);
    }
    auto parrinelloRahmanVelocityScaling = ParrinelloRahmanVelocityScaling::No;
    if (doParrinelloRahman)
    {
        parrinelloRahmanVelocityScaling = ParrinelloRahmanVelocityScaling::Diagonal;
        GMX_ASSERT(prVelocityScalingMatrix(YY, XX) == 0 && prVelocityScalingMatrix(ZZ, XX) == 0
                           && prVelocityScalingMatrix(ZZ, YY) == 0 && prVelocityScalingMatrix(XX, YY) == 0
                           && prVelocityScalingMatrix(XX, ZZ) == 0 && prVelocityScalingMatrix(YY, ZZ) == 0,
                   "Fully anisotropic Parrinello-Rahman pressure coupling is not yet supported "
                   "in GPU version of Leap-Frog integrator.");
        prVelocityScalingMatrixDiagonal_ = Float3{ dtPressureCouple * prVelocityScalingMatrix(XX, XX),
                                                   dtPressureCouple * prVelocityScalingMatrix(YY, YY),
                                                   dtPressureCouple * prVelocityScalingMatrix(ZZ, ZZ) };
    }

    launchLeapFrogKernel(numAtoms_,
                         d_x,
                         d_xp,
                         d_v,
                         d_f,
                         d_inverseMasses_,
                         dt,
                         doTemperatureScaling,
                         numTempScaleValues_,
                         d_tempScaleGroups_,
                         d_lambdas_,
                         parrinelloRahmanVelocityScaling,
                         prVelocityScalingMatrixDiagonal_,
                         deviceStream_);
}

LeapFrogGpu::LeapFrogGpu(const DeviceContext& deviceContext,
                         const DeviceStream&  deviceStream,
                         const int            numTempScaleValues) :
    deviceContext_(deviceContext), deviceStream_(deviceStream), numTempScaleValues_(numTempScaleValues)
{
    numAtoms_ = 0;

    changePinningPolicy(&h_lambdas_, gmx::PinningPolicy::PinnedIfSupported);

    // If the temperature coupling is enabled, we need to make space for scaling factors
    if (numTempScaleValues_ > 0)
    {
        h_lambdas_.resize(numTempScaleValues_);
        reallocateDeviceBuffer(
                &d_lambdas_, numTempScaleValues_, &numLambdas_, &numLambdasAlloc_, deviceContext_);
    }
}

LeapFrogGpu::~LeapFrogGpu()
{
    // Wait for all the tasks to complete before freeing the memory. See #4519.
    deviceStream_.synchronize();
    freeDeviceBuffer(&d_inverseMasses_);
}

void LeapFrogGpu::set(const int                            numAtoms,
                      const ArrayRef<const real>           inverseMasses,
                      const ArrayRef<const unsigned short> tempScaleGroups)
{
    numAtoms_ = numAtoms;

    reallocateDeviceBuffer(
            &d_inverseMasses_, numAtoms_, &numInverseMasses_, &numInverseMassesAlloc_, deviceContext_);
    copyToDeviceBuffer(
            &d_inverseMasses_, inverseMasses.data(), 0, numAtoms_, deviceStream_, GpuApiCallBehavior::Sync, nullptr);

    // Temperature scale group map only used if there are more than one group
    if (numTempScaleValues_ > 1)
    {
        reallocateDeviceBuffer(
                &d_tempScaleGroups_, numAtoms_, &numTempScaleGroups_, &numTempScaleGroupsAlloc_, deviceContext_);
        copyToDeviceBuffer(&d_tempScaleGroups_,
                           tempScaleGroups.data(),
                           0,
                           numAtoms_,
                           deviceStream_,
                           GpuApiCallBehavior::Sync,
                           nullptr);
    }
}

} // namespace gmx
