Fix Distributed Fused Adam Issues

[alpha0422]

What does this PR do ?

This PR fixes distributed optimizer issues:

1. Support NHWC layout, as required by Diffusion models;
2. Fix complex zero_grad() being not captured by CUDA graph;
3. Add option to distribute states within node;

Collection: [Note which collection this PR will affect]

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[timmoon10]

Overall looks good, although we are still hashing out the design in NVIDIA/apex#1794. As discussed in NVIDIA/apex#1794 (comment), I think we should set MegatronDistributedFusedAdam._step_support_amp_scaling=False to signal that the NeMo grad scaler can accommodate the distributed optimizer (unlike the plain PyTorch grad scaler). As a bonus, this approach fixes the grad scaling issue even without needing to update Apex.

[alpha0422]

Overall looks good, although we are still hashing out the design in NVIDIA/apex#1794. As discussed in NVIDIA/apex#1794 (comment), I think we should set MegatronDistributedFusedAdam._step_support_amp_scaling=False to signal that the NeMo grad scaler can accommodate the distributed optimizer (unlike the plain PyTorch grad scaler). As a bonus, this approach fixes the grad scaling issue even without needing to update Apex.

You are probably right, to make sure it won't hurt perf I need to confirm with our usecases. Anyway, I think that relates to the changes in APEX, the changes here have no relation to gradient clipping.

[ericharper]

LGTM. Thanks!

_step_support_amp_scaling=False will be considered in a future PR once perf is verified.

Agreed offline it could be dismissed.

[ericharper]

jenkins

[ericharper]

jenkins