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Benchmark comms with the exact sequence in Stencil as it is now.

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Peter Boyle
2026-08-22 17:14:10 -04:00
parent 1e287b6b30
commit a9c22d787a
1 changed files with 125 additions and 0 deletions
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benchmarks/Benchmark_comms_host_device.cc
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@@ -252,6 +252,131 @@ int main (int argc, char ** argv)
}
/////////////////////////////////////////////////////////////////////////////
// Halo exchange through the PRODUCTION stencil path.
//
// Prepare -> PollDtoH -> CopySynchronise -> Begin -> PollIRecv -> Complete
//
// verbatim as CartesianStencil::CommunicateBegin/Complete drive it, so this
// measures the code that actually runs inside the Dslash rather than a
// simplified stand-in built on SendToRecvFrom.
//
// THREE byte counts are reported, because they differ and conflating them
// has already produced an impossible number (272 GB/s/node against a
// 200 GB/s wire):
//
// offered : the whole halo this rank presents, all 8 directions.
// off-node : the subset whose partner is on another node, classified
// GEOMETRICALLY via IsOffNode() -- independent of --shm-mpi.
// to-MPI : what StencilSendToRecvFrom{Prepare,Begin} actually handed to
// MPI, i.e. their return value, exactly as the Stencil counts
// it. Under --shm-mpi 1 Grid delegates intranode transfers to
// MPI as well, so this approaches "offered"; under --shm-mpi 0
// Grid moves them itself and this approaches "off-node".
//
// Only the off-node column may be compared against wire speed.
/////////////////////////////////////////////////////////////////////////////
std::cout<<GridLogMessage << "===================================================================================================="<<std::endl;
std::cout<<GridLogMessage << "= Benchmarking STENCIL-PATH halo exchange from GPU memory "<<std::endl;
std::cout<<GridLogMessage << "===================================================================================================="<<std::endl;
std::cout<<GridLogMessage << " L Ls offered off-node to-MPI time off-node to-MPI"<<std::endl;
std::cout<<GridLogMessage << " MB/nd MB/nd MB/nd us/call GB/s/nd GB/s/nd"<<std::endl;
for(int lat=8;lat<=maxlat;lat+=4){
for(int Ls=8;Ls<=8;Ls*=2){
Coordinate latt_size ({lat*mpi_layout[0],
lat*mpi_layout[1],
lat*mpi_layout[2],
lat*mpi_layout[3]});
GridCartesian Grid(latt_size,simd_layout,mpi_layout);
RealD Nrank = Grid._Nprocessors;
RealD Nnode = Grid.NodeCount();
uint64_t bytes = (uint64_t)lat*lat*lat*Ls*sizeof(HalfSpinColourVectorD);
std::vector<HalfSpinColourVectorD *> xbuf(8), rbuf(8);
for(int d=0;d<8;d++){
xbuf[d] = (HalfSpinColourVectorD *)acceleratorAllocDevice(bytes);
rbuf[d] = (HalfSpinColourVectorD *)acceleratorAllocDevice(bytes);
}
// Packet table in the same shape the Stencil builds: 8 directions,
// to/from ranks from ShiftedRanks, participation gated on mpi_layout.
// COMPACT packet list, exactly as the Stencil builds it: only the
// directions that actually communicate get a packet. Passing a
// self-send with do_send=0 is not equivalent -- the assert
// "dest != _processor" in StencilSendToRecvFromBegin is unconditional.
std::vector<int> to_rank, from_rank, buf_id;
double offered = 0.0, offnode = 0.0;
for(int mu=0;mu<4;mu++){
if ( mpi_layout[mu] > 1 ) {
int s,d;
Grid.ShiftedRanks(mu,+1,s,d); to_rank.push_back(d); from_rank.push_back(s); buf_id.push_back(mu);
Grid.ShiftedRanks(mu,-1,s,d); to_rank.push_back(d); from_rank.push_back(s); buf_id.push_back(mu+4);
}
}
int npkt = to_rank.size();
for(int i=0;i<npkt;i++){
offered += 2.0*bytes; // send + receive
if ( Grid.IsOffNode(to_rank[i]) ) offnode += 2.0*bytes;
}
double mpibytes = 0.0, t = 0.0;
std::vector<CommsRequest_t> reqs;
for(int n=0;n<Nloop;n++){
reqs.resize(0);
double mb = 0.0;
Grid.StencilBarrier();
double t0=usecond();
for(int i=0;i<npkt;i++){
mb += Grid.StencilSendToRecvFromPrepare(reqs,
(void *)xbuf[buf_id[i]], to_rank[i], 1,
(void *)rbuf[buf_id[i]], from_rank[i], 1,
bytes,bytes,i);
}
Grid.StencilSendToRecvFromPollDtoH(reqs); /* Starts MPI */
acceleratorCopySynchronise();
for(int i=0;i<npkt;i++){
// xmit and xmit_comp identical: no compression in this benchmark
mb += Grid.StencilSendToRecvFromBegin(reqs,
(void *)xbuf[buf_id[i]],(void *)xbuf[buf_id[i]], to_rank[i], 1,
(void *)rbuf[buf_id[i]],(void *)rbuf[buf_id[i]], from_rank[i], 1,
bytes,bytes,i);
}
Grid.StencilSendToRecvFromPollIRecv(reqs);
Grid.StencilSendToRecvFromComplete(reqs,0);
t += usecond()-t0;
mpibytes += mb;
}
// Sum bytes over the machine, average the time over ranks, report per
// node. Reduced once, outside the timed region. bytes/us == MB/s.
double sumMpi = mpibytes; Grid.GlobalSum(sumMpi);
double sumOff = offnode*Nloop; Grid.GlobalSum(sumOff);
double sumAll = offered*Nloop; Grid.GlobalSum(sumAll);
double sumT = t; Grid.GlobalSum(sumT);
double avgT = sumT/Nrank;
std::cout<<GridLogMessage
<< std::setw(4) << lat <<" "<< std::setw(4) << Ls
<<" "<< std::setw(9) << sumAll/Nloop/Nnode/1.0e6
<<" "<< std::setw(9) << sumOff/Nloop/Nnode/1.0e6
<<" "<< std::setw(9) << sumMpi/Nloop/Nnode/1.0e6
<<" "<< std::setw(9) << avgT/Nloop
<<" "<< std::setw(8) << sumOff/avgT/Nnode/1000.0
<<" "<< std::setw(8) << sumMpi/avgT/Nnode/1000.0
<<std::endl;
for(int d=0;d<8;d++){
acceleratorFreeDevice(xbuf[d]);
acceleratorFreeDevice(rbuf[d]);
}
}
}
std::cout<<GridLogMessage << "===================================================================================================="<<std::endl;
std::cout<<GridLogMessage << "= All done; Bye Bye"<<std::endl;
std::cout<<GridLogMessage << "===================================================================================================="<<std::endl;