fix: #1432 TE RMS Norm numerical Instability#1681
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JiwaniZakir wants to merge 1 commit intoNVIDIA-NeMo:mainfrom
Open
fix: #1432 TE RMS Norm numerical Instability#1681JiwaniZakir wants to merge 1 commit intoNVIDIA-NeMo:mainfrom
JiwaniZakir wants to merge 1 commit intoNVIDIA-NeMo:mainfrom
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Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
JiwaniZakir
requested review from
HuiyingLi,
ZhiyuLi-Nvidia,
adil-a,
akoumpa,
hemildesai and
pthombre
as code owners
Contributor
|
Hi @JiwaniZakir thanks for making this, do you have a wandb that you can share showing the improved stability? Since this change is at a module level, it will affect all models using it, so i want to make sure we have a good understanding/review of the change. Thank you. |
Contributor
|
/claude review |
![claude[bot]](https://avatars.githubusercontent.com/in/1236702?s=60&v=4){kind=small}
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| """The TE RMSNorm patch must upcast bf16 inputs to fp32 before the kernel call.""" | ||
| captured = {} | ||
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| def mock_original_forward(self_inner, x): | ||
| captured["dtype"] = x.dtype | ||
| return x # pass-through | ||
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| instance = MagicMock() | ||
| x_bf16 = torch.randn(2, 4, dtype=torch.bfloat16) | ||
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| # Replicate the patched forward logic from _make_lazy_te_patcher | ||
| input_dtype = x_bf16.dtype | ||
| if input_dtype != torch.float32: | ||
| result = mock_original_forward(instance, x_bf16.float()) | ||
| else: | ||
| result = mock_original_forward(instance, x_bf16) | ||
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| assert captured["dtype"] == torch.float32, "TE RMSNorm should receive fp32 inputs after upcast patch" |
Contributor
There was a problem hiding this comment.
This test re-implements the patch logic inline rather than invoking the actual _patched_rmsnorm_forward. If the real patch logic drifts, this test will still pass.
More concretely, it also doesn't verify the .to(input_dtype) cast-back — the result variable is never checked for dtype. Consider adding:
assert result.dtype == torch.bfloat16, "Result should be cast back to the original input dtype"
Contributor
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Hi, @JiwaniZakir Thank you for the PR! As for the next step, could you help us with
Let us know what you think. |
akoumpa
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Closes #1432
What does this PR do ?
Fix numerical instability in TE RMSNorm by upcasting non-fp32 inputs to float32 before the kernel call, then casting outputs back to the original dtype.
Changelog
nemo_automodel/components/models/common/utils.py: In_make_lazy_te_patcher,_patched_rmsnorm_forwardnow capturesinput_dtypeand, when the input is not alreadyfloat32, calls_original_rmsnorm_forwardwithx.float()and casts the result back toinput_dtypebefore returning.tests/unit_tests/models/common/test_model_common_utils.py: AddedTestFloat32RMSNormtest class with four tests covering:Float32RMSNormweight dtype preservation, output dtype consistency through the fp32 computation path, numerical accuracy comparison between fp32-upcast and native bf16 norm against a float64 reference, and verification that the TE RMSNorm patch passes fp32 tensors to the underlying kernel.Before your PR is "Ready for review"
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Additional Information
This PR was created with AI assistance (Claude). The changes were reviewed by quality gates and a critic model before submission.