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Adding ring all reduce for large vectors

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This commit is contained in:
Peter Boyle
2026-08-25 12:07:11 -04:00
parent dbbd5dba35
commit 167753aa3f
7 changed files with 607 additions and 6 deletions
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Grid/algorithms/multigrid/DenseCoarseMatrix.h
+12 -4
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@@ -251,11 +251,13 @@ public:
for(int j=0;j<NK;j++) h[j] = &dPartial[0] + (uint64_t)j*nrows*MRHS_MAX; // compact, ldc=nrows
acceleratorCopyToDevice(&h[0],&cptrs[0],NK*sizeof(ComplexF*));
devSum = getenv("DENSE_DEVICE_SUM") ? 1 : 0;
devSum = getenv("DENSE_DEVICE_SUM") ? atoi(getenv("DENSE_DEVICE_SUM")) : 0;
const char *sumName[4] = {"host allreduce","DEVICE-buffer allreduce (GPU-aware MPI)",
"DEVICE cartesian ring allreduce (P2P)","DEVICE flat ring allreduce (P2P)"};
GRID_ASSERT(devSum>=0 && devSum<=3);
std::cout << GridLogMessage << "DenseCoarseMatrix: slab resident on device ("
<< sbytes/1024./1024. << " MB/rank), split-K NK=" << NK << " (Kc=" << Kc << "); "
<< (devSum ? "DEVICE-buffer allreduce (GPU-aware MPI)" : "host allreduce")
<< std::endl;
<< sumName[devSum] << std::endl;
}
////////////////////////////////////////////////////////////////////
@@ -961,7 +963,13 @@ public:
}
t2 = usecond();
{ GRID_TRACE("DenseAllreduce");
grid->GlobalSumVector((ComplexF *)&dX[0], (int)nX);
// DENSE_DEVICE_SUM=1 : device-buffer MPI_Allreduce (Cray MPICH aborts
// above ~8 MB: 12 RHS at N=138240 is 13.3 MB)
// DENSE_DEVICE_SUM=2 : CartesianRingAllReduce, P2P only, no size cliff
// DENSE_DEVICE_SUM=3 : flat RingAllReduce, P2P only
if (devSum==2) CartesianRingAllReduce(grid,(ComplexF *)&dX[0],nX);
else if (devSum==3) RingAllReduce(grid,(ComplexF *)&dX[0],nX);
else grid->GlobalSumVector((ComplexF *)&dX[0], (int)nX);
}
t3 = usecond();
} else {