fix performance issue in convnext DDP train

[cybergeek2077]

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Motivation

There are flowing warning when use dist_train.sh to train convnext

[W reducer.cpp:347] Warning: Grad strides do not match bucket view strides. This may indicate grad was not created according to the gradient layout contract, or that the param's strides changed since DDP was constructed. This is not an error, but may impair performance.

Modification

call contiguous after permute in layernorm, and the performance actually improve 3x in my test

BC-breaking (Optional)

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Checklist

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• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

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[CLAassistant]

All committers have signed the CLA.

[mzr1996]

LGTM, I have tested it and this modification can slightly accelerate the training.

[kamzero]

the performance actually improve 3x in my test

Hi! May I ask whether this warning only affects the training speed and convergence speed, or will it affect the accuracy?

[cybergeek2077]

the performance actually improve 3x in my test

Hi! May I ask whether this warning only affects the training speed and convergence speed, or will it affect the accuracy?

I do not do the ablation experiment, but the model i trained before fixing the bug works normally, so i think it only affects the training speed.

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