chrishkchris edited a comment on issue #14: rearrange contents in dist-train.md URL: https://github.com/apache/singa-doc/pull/14#issuecomment-608995695 > Is nccl_id passed to `train_mnist_cnn` for training with MPI? No, in the case of MPI, nccl_id is generated and immediately broadcasted by MPI from rank0 to every rank. https://github.com/apache/singa/blob/master/src/io/communicator.cc#L102 ``` if (MPIRankInGlobal == 0) ncclGetUniqueId(&id); MPICHECK(MPI_Bcast((void *)&id, sizeof(id), MPI_BYTE, 0, MPI_COMM_WORLD)); ``` > For multiprocessing, num_gpu = gpu_per_node, hence we only need num_gpu? This is reserve for future use, because previously I planned using network socket to broadcast ncclid to other nodes instead of MPI.
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