add explanation of SplitInferenceModule

Author: a-r-r-o-w

src/diffusers/pipelines/free_noise_utils.py

@@ -50,19 +50,65 @@ def __init__(
         self.input_kwargs_to_split = set(input_kwargs_to_split)
 
     def forward(self, *args, **kwargs) -> Union[torch.Tensor, Tuple[torch.Tensor]]:
-        r"""Forward method of `SplitInferenceModule`.
+        r"""Forward method for the `SplitInferenceModule`.
 
-        All inputs that should be split should be passed as keyword arguments. Only those keywords arguments will be
-        split that are specified in `inputs_to_split` when initializing the module.
+        This method processes the input by splitting specified keyword arguments along a given dimension, running the
+        underlying module on each split, and then concatenating the results. The splitting is controlled by the
+        `split_size` and `split_dim` parameters specified during initialization.
+
+        Args:
+            *args (`Any`):
+                Positional arguments that are passed directly to the `module` without modification.
+            **kwargs (`Dict[str, torch.Tensor]`):
+                Keyword arguments passed to the underlying `module`. Only keyword arguments whose names match the
+                entries in `input_kwargs_to_split` and are of type `torch.Tensor` will be split. The remaining keyword
+                arguments are passed unchanged.
+
+        Returns:
+            `Union[torch.Tensor, Tuple[torch.Tensor]]`:
+                The outputs obtained from `SplitInferenceModule` are the same as if the underlying module was inferred
+                without it.
+                - If the underlying module returns a single tensor, the result will be a single concatenated tensor
+                along the same `split_dim` after processing all splits.
+                - If the underlying module returns a tuple of tensors, each element of the tuple will be concatenated
+                along the `split_dim` across all splits, and the final result will be a tuple of concatenated tensors.
+
+        Workflow:
+            1. The keyword arguments specified in `input_kwargs_to_split` are split into smaller chunks using
+            `torch.split()` along the dimension `split_dim` and with a chunk size of `split_size`.
+            2. The `module` is invoked once for each split with both the split inputs and any unchanged arguments
+            that were passed.
+            3. The output tensors from each split are concatenated back together along `split_dim` before returning.
+
+        Example:
+            ```python
+            >>> import torch
+
+            >>> model = nn.Linear(1000, 1000)
+            >>> split_module = SplitInferenceModule(
+            ...     model, split_size=2, split_dim=0, input_kwargs_to_split=["input_data"]
+            ... )
+
+            >>> input_tensor = torch.randn(42, 1000)
+            >>> # Will split the tensor into 21 slices of shape [2, 1000].
+            >>> output = split_module(input_data=input_tensor)
+            ```
+
+        This method is useful when you need to perform inference on large tensors in a memory-efficient way by breaking
+        them into smaller chunks, processing each chunk separately, and then reassembling the results.
+
+        It is also possible to nest `SplitInferenceModule` across different split dimensions.
         """
         split_inputs = {}
 
+        # 1. Split inputs that were specified during initialization and also present in passed kwargs
         for key in list(kwargs.keys()):
             if key not in self.input_kwargs_to_split or not torch.is_tensor(kwargs[key]):
                 continue
             split_inputs[key] = torch.split(kwargs[key], self.split_size, self.split_dim)
             kwargs.pop(key)
 
+        # 2. Invoke forward pass across each split
         results = []
         for split_input in zip(*split_inputs.values()):
             inputs = dict(zip(split_inputs.keys(), split_input))
@@ -71,6 +117,7 @@ def forward(self, *args, **kwargs) -> Union[torch.Tensor, Tuple[torch.Tensor]]:
             intermediate_tensor_or_tensor_tuple = self.module(*args, **inputs)
             results.append(intermediate_tensor_or_tensor_tuple)
 
+        # 3. Concatenate split restuls to obtain final outputs
         if isinstance(results[0], torch.Tensor):
             return torch.cat(results, dim=self.split_dim)
         elif isinstance(results[0], tuple):