NCCL Tests

This page explains how to verify multi-node GPU communication using nccl-tests.

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📦 Build

cd 10-nccl-tests
make build

This builds the Docker image containing nccl-tests.

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▶️ Run

bash run_mpi.sh ./hostfile.example

• hostfile.example defines the nodes participating in the test:

  node0 slots=1
  node1 slots=1
  node2 slots=1
  node3 slots=1
  

• The script launches an AllReduce performance benchmark across nodes.

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📊 Example Output

# nThread 1 nGpus 1 minBytes 8 maxBytes 1073741824 step: 2(factor)
#
# Rank  Latency(us)   Bus BW(GB/s)
0-1    11.25         162.3

This confirms NCCL communication over RDMA + Infiniband/RoCE is working properly.

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🖼️ Architecture Reference