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Fix potential deadlock during NCCL local communicator creation. #98

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Merged
romerojosh merged 3 commits into from
Jan 22, 2026
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Fix potential deadlock during NCCL local communicator creation. #98

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46a2e9e
Fix potential deadlock during NCCL local communicator creation.
romerojosh Jan 21, 2026
f22dce0
Use clique comm when needed.
romerojosh Jan 21, 2026
40eadb7
Formatting.
romerojosh Jan 21, 2026
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12 changes: 10 additions & 2 deletions src/cudecomp.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -655,8 +655,16 @@ cudecompResult_t cudecompGridDescCreate(cudecompHandle_t handle, cudecompGridDes
setCommInfo(handle, grid_desc, col_comm, CUDECOMP_COMM_COL);

// Create local NCCL communicator if row or column communicator uses it
if ((grid_desc->row_comm_info.ngroups == 1 && grid_desc->row_comm_info.nranks > 1) ||
(grid_desc->col_comm_info.ngroups == 1 && grid_desc->col_comm_info.nranks > 1)) {
int need_local_nccl_comm =
static_cast<int>((grid_desc->row_comm_info.ngroups == 1 && grid_desc->row_comm_info.nranks > 1) ||
(grid_desc->col_comm_info.ngroups == 1 && grid_desc->col_comm_info.nranks > 1));

// Local comm can include ranks in other rows/columns, need additional check for those cases.
CHECK_MPI(MPI_Allreduce(MPI_IN_PLACE, &need_local_nccl_comm, 1, MPI_INT, MPI_LOR,
handle->mpi_clique_comm != MPI_COMM_NULL ? handle->mpi_clique_comm
: handle->mpi_local_comm));

if (need_local_nccl_comm) {
handle->nccl_local_comm = ncclCommFromMPIComm(
handle->mpi_clique_comm != MPI_COMM_NULL ? handle->mpi_clique_comm : handle->mpi_local_comm);
}
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