Fix to peft & virtual pipeline parallel unsupported check

[vysarge]

What does this PR do ?

Corrects the check added in PR-7964 to raise a ValueError when attempting to run virtual pipeline parallel with peft.

Collection: nlp/language_modeling

Changelog

• Moves this safety check from MegatronGPTSFTModel.__init__ (where self.use_peft had not yet been set to true, so the check did not function) to NLPAdapterModelMixin.add_adapter

Usage

Running with the unsupported combination of peft and virtual pipeline parallel now yields a more useful error message:

python examples/nlp/language_modeling/tuning/megatron_gpt_peft_tuning.py \
    ++model.virtual_pipeline_model_parallel_size=10 \
    ++model.peft.peft_scheme=lora \
    ...

gives

  File "/opt/NeMo/examples/nlp/language_modeling/tuning/megatron_gpt_peft_tuning.py", line 73, in main
    model.add_adapter(peft_cfg_cls(model_cfg))
  File "/opt/NeMo/nemo/collections/nlp/parts/mixins/nlp_adapter_mixins.py", line 178, in add_adapter
    raise ValueError('Virtual pipeline model parallel is not supported when using PEFT')

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[vysarge]

@cuichenx / @ericharper can you review? Thanks!

[ericharper]

jenkins

[erhoo82]

LGTM