def pre_logits(self, feats: Tuple[torch.Tensor]) -> torch.Tensor:
        """The process before the final classification head.

        The input ``feats`` is a tuple of tensor, and each tensor is the
        feature of a backbone stage.
        """
        x = feats[-1]
        for layer in self.layers[:-1]:
            x = layer(x)
        return x
The process before the final classification head.

        The input ``feats`` is a tuple of tensor, and each tensor is the
        feature of a backbone stage.
        
mmpretrain/models/heads/stacked_head.py