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add tips to force NCCL comm to go through EFA #531

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add tips to force NCCL comm to go through EFA
KeitaW Jan 23, 2025
ebb0711
Update micro-benchmarks/nccl-tests/README.md
mhuguesaws Jan 23, 2025
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Update micro-benchmarks/nccl-tests/README.md
KeitaW Jan 23, 2025
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22 changes: 22 additions & 0 deletions micro-benchmarks/nccl-tests/README.md
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Expand Up @@ -316,3 +316,25 @@ The formula defines the maximum theoretical bandwidth that can be achieved on di
* `t` : time to complete the operation. (similar to sec for Algbw and Busbw)
* `S` : number of elements being communicated (similar to count for Algbw and Busbw)
* `B` : theoretical peak bandwidth.

## 4. Tips and Tricks
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Please find another title.

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Other usages?


This section demonstrates NCCL tests tips and tricks useful to diagnose cluster nodes.
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How do we know if this is bad or good?

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If the test works till the end -> good. Otherwise bad?

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We should set expected performance on single instance.


#### Test EFA

You can force inter-GPU communications to go through EFA network interfaces instead of shared memory of NVLink with the following environment variables:


```bash
#Single node EFA
# libfabric flags
export FI_PROVIDER=efa
export FI_EFA_USE_DEVICE_RDMA=1

# NCCL Environment force disable P2P through NVlink, PCI and SHM.
export NCCL_P2P_DISABLE=1
export NCCL_SHM_DISABLE=1
export NCCL_NVLS_ENABLE=0
export NCCL_NET='AWS Libfabric'
```