Cross Entropy Loss and loss of PyTorch Lightning does not matches
Hi, I am working on building a question and answering model using T5(Huggingface) with PyTorch Lightning Module and I am checking my loss and PyTorch Lightning Loss is not being matched.
class UQAFineTuneModel(pl.LightningModule):
    def __init__(self):
        super().__init__()
        self.model = T5ForConditionalGeneration.from_pretrained(
            "allenai/unifiedqa-t5-small", return_dict=True
        )
        self.model.train()
    def forward(
        self,
        source_text_input_ids,
        source_text_attention_mask,
        target_text_input_ids=None,
    ):
        output = self.model(
            input_ids=source_text_input_ids,
            attention_mask=source_text_attention_mask,
            labels=target_text_input_ids,
        )
        return output.loss, output.logits

    def training_step(self, batch, batch_idx):
        source_text_input_ids = batch["source_text_input_ids"]
        source_text_attention_mask = batch["source_text_attention_mask"]
        target_text_input_ids = batch["target_text_input_ids"]
        # labels_attention_mask = batch["target_text_attention_mask"]
        loss, outputs = self(
            source_text_input_ids, source_text_attention_mask, target_text_input_ids
        ) 
        loss_mine = None  
        output = self.model(
            input_ids=source_text_input_ids,
            attention_mask=source_text_attention_mask,
            labels=target_text_input_ids,
        ) 
        labels = batch["target_text_input_ids"].clone() 
        labels[labels == 0] = -100 
        if target_text_input_ids is not None:  
            loss_fct = CrossEntropyLoss(ignore_index=-100) 
            loss_mine = loss_fct(output.logits.view(-1, outputs.size(-1)), labels.view(-1)) 
            print(f"loss_Hugginface: {loss.item()}, loss_mine : {loss_mine.item()}") 
        self.log("train_loss", loss, prog_bar=True, logger=True)
        return {"loss": loss, "predictions": outputs}


You can see the above image, why loss is not same, help is very much needed, I asked the same question on HuggingFace but they told me to ask here, you can view that discussion here.
Hey @ayush714,
I believe this is related to HF and you might get your answers by opening an issue on their repo directly.
Best,
T.C