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fix: the source part should not participate in loss calculation in SFT stage #762

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fix: the source part should not participate in loss calculation in SFT stage #762

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11 changes: 11 additions & 0 deletions applications/DeepSpeed-Chat/training/utils/data/data_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -175,6 +175,17 @@ def create_dataset_split(current_dataset, raw_dataset, train_phase, tokenizer,
0)
chosen_token["attention_mask"] = chosen_token[
"attention_mask"].squeeze(0)

# In the SFT stage, it's essential that the source part doesn't contribute to the loss calculation,
# only the completion part should be considered. Set ignore index to labels to -100, so that loss function will ignore the loss of source part.
# The specific value, -100, is the default value for ignore index in `toch.nn.CrossEntropyLoss`
# see https://pytorch.org/docs/stable/generated/torch.nn.CrossEntropyLoss.html#torch.nn.CrossEntropyLoss for more details
prompt_sentence = raw_dataset.get_prompt(tmp_data)
prompt_token = tokenizer(prompt_sentence, add_special_tokens=False)
prompt_token_len = min(max_seq_len, len(prompt_token["input_ids"]))
chosen_token["labels"] = chosen_token["input_ids"].clone()
chosen_token["labels"][:prompt_token_len] = -100

chosen_dataset.append(chosen_token)

elif train_phase == 2:
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