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337 lines
11 KiB
C++
337 lines
11 KiB
C++
#ifndef GRID_STENCIL_H
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#define GRID_STENCIL_H
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//////////////////////////////////////////////////////////////////////////////////////////
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// Must not lose sight that goal is to be able to construct really efficient
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// gather to a point stencil code. CSHIFT is not the best way, so need
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// additional stencil support.
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//
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// Stencil based code will pre-exchange haloes and use a table lookup for neighbours.
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// This will be done with generality to allow easier efficient implementations.
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// Overlap of comms and compute could be semi-automated by tabulating off-node connected,
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// and
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//
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// Lattice <foo> could also allocate haloes which get used for stencil code.
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//
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// Grid could create a neighbour index table for a given stencil.
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//
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// Could also implement CovariantCshift, to fuse the loops and enhance performance.
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//
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//
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// General stencil computation:
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//
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// Generic services
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// 0) Prebuild neighbour tables
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// 1) Compute sizes of all haloes/comms buffers; allocate them.
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//
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// 2) Gather all faces, and communicate.
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// 3) Loop over result sites, giving nbr index/offnode info for each
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//
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// Could take a
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// SpinProjectFaces
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// start comms
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// complete comms
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// Reconstruct Umu
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//
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// Approach.
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//
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//////////////////////////////////////////////////////////////////////////////////////////
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namespace Grid {
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class CartesianStencil { // Stencil runs along coordinate axes only; NO diagonal fill in.
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public:
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typedef uint32_t StencilInteger;
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StencilInteger alignup(StencilInteger n){
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n--; // 1000 0011 --> 1000 0010
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n |= n >> 1; // 1000 0010 | 0100 0001 = 1100 0011
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n |= n >> 2; // 1100 0011 | 0011 0000 = 1111 0011
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n |= n >> 4; // 1111 0011 | 0000 1111 = 1111 1111
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n |= n >> 8; // ... (At this point all bits are 1, so further bitwise-or
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n |= n >> 16; // operations produce no effect.)
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n++; // 1111 1111 --> 1 0000 0000
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return n;
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};
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void LebesgueOrder(void);
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std::vector<StencilInteger> _LebesgueReorder;
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int _checkerboard;
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int _npoints; // Move to template param?
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GridBase * _grid;
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// npoints of these
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std::vector<int> _directions;
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std::vector<int> _distances;
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std::vector<int> _comm_buf_size;
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std::vector<int> _permute_type;
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// npoints x Osites() of these
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std::vector<std::vector<int> > _offsets;
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std::vector<std::vector<int> > _is_local;
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std::vector<std::vector<int> > _permute;
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int _unified_buffer_size;
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int _request_count;
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CartesianStencil(GridBase *grid,
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int npoints,
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int checkerboard,
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const std::vector<int> &directions,
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const std::vector<int> &distances);
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// Add to tables for various cases; is this mistaken. only local if 1 proc in dim
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// Can this be avoided with simpler coding of comms?
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void Local (int point, int dimension,int shift,int cbmask);
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void Comms (int point, int dimension,int shift,int cbmask);
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void CopyPlane(int point, int dimension,int lplane,int rplane,int cbmask,int permute);
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void ScatterPlane (int point,int dimension,int plane,int cbmask,int offset);
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// Could allow a functional munging of the halo to another type during the comms.
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// this could implement the 16bit/32bit/64bit compression.
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template<class vobj,class cobj, class compressor> void
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HaloExchange(const Lattice<vobj> &source,std::vector<cobj,alignedAllocator<cobj> > &u_comm_buf,compressor &compress)
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{
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// conformable(source._grid,_grid);
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assert(source._grid==_grid);
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if (u_comm_buf.size() != _unified_buffer_size ) u_comm_buf.resize(_unified_buffer_size);
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int u_comm_offset=0;
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// Gather all comms buffers
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for(int point = 0 ; point < _npoints; point++) {
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compress.Point(point);
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int dimension = _directions[point];
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int displacement = _distances[point];
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int fd = _grid->_fdimensions[dimension];
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int rd = _grid->_rdimensions[dimension];
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// Map to always positive shift modulo global full dimension.
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int shift = (displacement+fd)%fd;
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int checkerboard = _grid->CheckerBoardDestination(source.checkerboard,shift);
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assert (checkerboard== _checkerboard);
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// the permute type
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int simd_layout = _grid->_simd_layout[dimension];
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int comm_dim = _grid->_processors[dimension] >1 ;
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int splice_dim = _grid->_simd_layout[dimension]>1 && (comm_dim);
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// Gather phase
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int sshift [2];
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if ( comm_dim ) {
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sshift[0] = _grid->CheckerBoardShift(_checkerboard,dimension,shift,0);
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sshift[1] = _grid->CheckerBoardShift(_checkerboard,dimension,shift,1);
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if ( sshift[0] == sshift[1] ) {
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if (splice_dim) {
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GatherStartCommsSimd(source,dimension,shift,0x3,u_comm_buf,u_comm_offset,compress);
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} else {
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GatherStartComms(source,dimension,shift,0x3,u_comm_buf,u_comm_offset,compress);
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}
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} else {
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if(splice_dim){
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GatherStartCommsSimd(source,dimension,shift,0x1,u_comm_buf,u_comm_offset,compress);// if checkerboard is unfavourable take two passes
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GatherStartCommsSimd(source,dimension,shift,0x2,u_comm_buf,u_comm_offset,compress);// both with block stride loop iteration
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} else {
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GatherStartComms(source,dimension,shift,0x1,u_comm_buf,u_comm_offset,compress);
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GatherStartComms(source,dimension,shift,0x2,u_comm_buf,u_comm_offset,compress);
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}
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}
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}
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}
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}
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template<class vobj,class cobj, class compressor>
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void GatherStartComms(const Lattice<vobj> &rhs,int dimension,int shift,int cbmask,
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std::vector<cobj,alignedAllocator<cobj> > &u_comm_buf,
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int &u_comm_offset,compressor & compress)
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{
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typedef typename cobj::vector_type vector_type;
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typedef typename cobj::scalar_type scalar_type;
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GridBase *grid=_grid;
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assert(rhs._grid==_grid);
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// conformable(_grid,rhs._grid);
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int fd = _grid->_fdimensions[dimension];
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int rd = _grid->_rdimensions[dimension];
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int pd = _grid->_processors[dimension];
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int simd_layout = _grid->_simd_layout[dimension];
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int comm_dim = _grid->_processors[dimension] >1 ;
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assert(simd_layout==1);
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assert(comm_dim==1);
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assert(shift>=0);
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assert(shift<fd);
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int buffer_size = _grid->_slice_nblock[dimension]*_grid->_slice_block[dimension];
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std::vector<cobj,alignedAllocator<cobj> > send_buf(buffer_size); // hmm...
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std::vector<cobj,alignedAllocator<cobj> > recv_buf(buffer_size);
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int cb= (cbmask==0x2)? 1 : 0;
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int sshift= _grid->CheckerBoardShift(rhs.checkerboard,dimension,shift,cb);
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for(int x=0;x<rd;x++){
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int sx = (x+sshift)%rd;
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int comm_proc = ((x+sshift)/rd)%pd;
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if (comm_proc) {
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int words = send_buf.size();
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if (cbmask != 0x3) words=words>>1;
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int bytes = words * sizeof(cobj);
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Gather_plane_simple (rhs,send_buf,dimension,sx,cbmask,compress);
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int rank = _grid->_processor;
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int recv_from_rank;
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int xmit_to_rank;
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_grid->ShiftedRanks(dimension,comm_proc,xmit_to_rank,recv_from_rank);
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assert (xmit_to_rank != _grid->ThisRank());
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assert (recv_from_rank != _grid->ThisRank());
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// FIXME Implement asynchronous send & also avoid buffer copy
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_grid->SendToRecvFrom((void *)&send_buf[0],
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xmit_to_rank,
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(void *)&recv_buf[0],
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recv_from_rank,
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bytes);
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for(int i=0;i<buffer_size;i++){
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u_comm_buf[u_comm_offset+i]=recv_buf[i];
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}
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u_comm_offset+=buffer_size;
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}
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}
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}
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template<class vobj,class cobj, class compressor>
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void GatherStartCommsSimd(const Lattice<vobj> &rhs,int dimension,int shift,int cbmask,
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std::vector<cobj,alignedAllocator<cobj> > &u_comm_buf,
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int &u_comm_offset,compressor &compress)
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{
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const int Nsimd = _grid->Nsimd();
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typedef typename cobj::vector_type vector_type;
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typedef typename cobj::scalar_type scalar_type;
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typedef typename cobj::scalar_object scalar_object;
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int fd = _grid->_fdimensions[dimension];
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int rd = _grid->_rdimensions[dimension];
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int ld = _grid->_ldimensions[dimension];
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int pd = _grid->_processors[dimension];
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int simd_layout = _grid->_simd_layout[dimension];
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int comm_dim = _grid->_processors[dimension] >1 ;
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assert(comm_dim==1);
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assert(simd_layout==2);
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assert(shift>=0);
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assert(shift<fd);
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int permute_type=_grid->PermuteType(dimension);
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///////////////////////////////////////////////
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// Simd direction uses an extract/merge pair
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///////////////////////////////////////////////
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int buffer_size = _grid->_slice_nblock[dimension]*_grid->_slice_block[dimension];
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int words = sizeof(cobj)/sizeof(vector_type);
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/*
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* possibly slow to allocate
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* Doesn't matter in this test, but may want to preallocate in the
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* dirac operators
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*/
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std::vector<std::vector<scalar_object> > send_buf_extract(Nsimd,std::vector<scalar_object>(buffer_size) );
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std::vector<std::vector<scalar_object> > recv_buf_extract(Nsimd,std::vector<scalar_object>(buffer_size) );
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int bytes = buffer_size*sizeof(scalar_object);
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std::vector<scalar_object *> pointers(Nsimd); //
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std::vector<scalar_object *> rpointers(Nsimd); // received pointers
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///////////////////////////////////////////
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// Work out what to send where
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///////////////////////////////////////////
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int cb = (cbmask==0x2)? 1 : 0;
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int sshift= _grid->CheckerBoardShift(rhs.checkerboard,dimension,shift,cb);
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// loop over outer coord planes orthog to dim
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for(int x=0;x<rd;x++){
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int any_offnode = ( ((x+sshift)%fd) >= rd );
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if ( any_offnode ) {
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for(int i=0;i<Nsimd;i++){
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pointers[i] = &send_buf_extract[i][0];
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}
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int sx = (x+sshift)%rd;
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Gather_plane_extract<cobj>(rhs,pointers,dimension,sx,cbmask,compress);
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for(int i=0;i<Nsimd;i++){
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int inner_bit = (Nsimd>>(permute_type+1));
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int ic= (i&inner_bit)? 1:0;
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int my_coor = rd*ic + x;
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int nbr_coor = my_coor+sshift;
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int nbr_proc = ((nbr_coor)/ld) % pd;// relative shift in processors
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int nbr_lcoor= (nbr_coor%ld);
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int nbr_ic = (nbr_lcoor)/rd; // inner coord of peer
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int nbr_ox = (nbr_lcoor%rd); // outer coord of peer
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int nbr_lane = (i&(~inner_bit));
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int recv_from_rank;
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int xmit_to_rank;
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if (nbr_ic) nbr_lane|=inner_bit;
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assert (sx == nbr_ox);
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if(nbr_proc){
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_grid->ShiftedRanks(dimension,nbr_proc,xmit_to_rank,recv_from_rank);
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_grid->SendToRecvFrom((void *)&send_buf_extract[nbr_lane][0],
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xmit_to_rank,
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(void *)&recv_buf_extract[i][0],
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recv_from_rank,
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bytes);
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rpointers[i] = &recv_buf_extract[i][0];
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} else {
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rpointers[i] = &send_buf_extract[nbr_lane][0];
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}
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}
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// Here we don't want to scatter, just place into a buffer.
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for(int i=0;i<buffer_size;i++){
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assert(u_comm_offset+i<_unified_buffer_size);
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merge(u_comm_buf[u_comm_offset+i],rpointers,i);
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}
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u_comm_offset+=buffer_size;
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}
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}
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}
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};
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}
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#endif
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