fix: fix nccl P2P initialization error for non-colocated #636
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Signed-off-by: Zhanda <[email protected]>
Signed-off-by: Zhanda <[email protected]>
yuki-97
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Jul 10, 2025
Signed-off-by: Zhanda Zhu <[email protected]>
wangshangsam
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Jul 10, 2025
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Hmmm ... I was looking into the mypy errors in #632 until I realized that mypy failed for this PR too. It would be hard to imagine why this PR would trigger any mypy failures. @terrykong @parthchadha is mypy failing expected? |
Contributor
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@wangshangsam the mypy job is expected to fail. It won't block a PR, but just as an FYI of typing issues. Once we're completely in the green, we'll change that so it gates PRs |
parthchadha
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Jul 10, 2025
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Signed-off-by: Zhanda <[email protected]> Signed-off-by: Zhanda Zhu <[email protected]> Co-authored-by: Zhanda Zhu <[email protected]> Signed-off-by: Zhiyu Li <[email protected]>
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What does this PR do ?
Adds explicit
NCCL_CUMEM_ENABLE=1environment variable setting to resolve P2P initialization failures in distributed training with vLLM.Please see detailed analysis in #564 (comment).
Issues
Closes #564.
This PR can also be helpful to #613. Maybe @YUki-666 could take a look. The only change you may need to make it to delete the
os.environ["NCCL_CUMEM_ENABLE"] = "0"in functioninit_collectivefornemo_rl/models/policy/megatron_policy_worker.py.Test results
I have tested the settings @YUki-666 provided: 8b model grpo on 5 nodes:
Where
exp1_5n_non_colocated_p2p_disabled: before the fix, running withNCCL_P2P_DISABLE=1.exp2_5n_non_colocated_fix: after this pr's fix.We can see that:
Usage
The fix automatically applies when using distributed training with vLLM generation workers. No user action required.
Additional Information
This PR works for both the current
vllm==0.9.0and also new versions likevllm>=0.9.1rc1.If we upgrade our version, we can remove the additional environment variable setting in
nemo_rl/models/generation/vllm_backend.py.