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Grid/lib/Stencil.h
Peter Boyle f9b070d64d Reorganise of file naming
2015-06-03 12:47:05 +01:00

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