[pipeline] refactor 1f1b schedule (#4115)

* [api] update optimizer wrapper to fit pipeline

* [pipeline] add base schedule

* [pipeline] add 1f1b schedule

* [test] add pipeline schedule utils test

* [pipeline] fix import

colossalai/pipeline/schedule/_utils.py

@@ -0,0 +1,129 @@
+from typing import Any, List, Optional
+
+import torch
+import torch.cuda
+from torch.nn import Module
+from torch.utils._pytree import tree_flatten, tree_map, tree_unflatten
+
+
+def to_device(x: Any, device: Optional[torch.device] = None) -> Any:
+    """Move object to device if it is a tensor.
+
+    Args:
+        x (Any): Object to be moved.
+        device (Optional[torch.device], optional): Target device. Defaults to None.
+
+    Returns:
+        Any: Moved object.
+    """
+    if isinstance(x, torch.Tensor):
+        return x.to(device)
+    return x
+
+
+def get_batch_size(batch: Any) -> int:
+    """Get the batch size (size of dimension-0) of the first tensor in the batch.
+
+    Args:
+        batch (Any): Batch to be inspected.
+
+    Raises:
+        RuntimeError: If no tensor is found in the batch.
+
+    Returns:
+        int: Batch size.
+    """
+    data_list, _ = tree_flatten(batch)
+    for data in data_list:
+        if isinstance(data, torch.Tensor):
+            return data.size(0)
+    raise RuntimeError('No tensor found in the batch')
+
+
+def get_micro_batch(batch: Any, start: int, micro_batch_size: int) -> Any:
+    """Get a micro batch of the original batch.
+
+    Args:
+        batch (Any): Batch to be sliced.
+        start (int): Start index of the micro batch.
+        micro_batch_size (int): Size of the micro batch.
+
+    Returns:
+        Any: Target micro batch.
+    """
+
+    def _get_tensor_slice(x: Any):
+        if isinstance(x, torch.Tensor):
+            return x[start:start + micro_batch_size]
+        return x
+
+    return tree_map(_get_tensor_slice, batch)
+
+
+def model_forward(model: Module, data: Any, internal_inputs: Optional[dict]) -> Any:
+    """Call model forward function with data and internal inputs.
+
+    Args:
+        model (Module): Model to be called.
+        data (Any): Data loaded from data iterator.
+        internal_inputs (Optional[dict]): Data from previous stage. It must be a dict or None if it's the first stage.
+
+    Returns:
+        Any: Outputs of the model.
+    """
+    if internal_inputs is None:
+        internal_inputs = {}
+    if isinstance(data, (list, tuple)):
+        return model(*data, **internal_inputs)
+    elif isinstance(data, dict):
+        return model(**data, **internal_inputs)
+    return model(data, **internal_inputs)
+
+
+def retain_grad(x: Any) -> None:
+    """Call retain_grad() on a tensor.
+
+    Args:
+        x (Any): Object to be called.
+    """
+    if isinstance(x, torch.Tensor):
+        x.retain_grad()
+
+
+def detach(x: Any) -> Any:
+    """Call detach() on a tensor.
+
+    Args:
+        x (Any): Object to be called.
+
+    Returns:
+        Any: The detached object.
+    """
+    if isinstance(x, torch.Tensor):
+        return x.detach()
+    return x
+
+
+def merge_batch(data: List[Any]) -> Any:
+    """Merge micro batches into a batch.
+
+    Args:
+        data (List[Any]): A list of micro batches.
+
+    Returns:
+        Any: Merge batch.
+    """
+    if len(data) == 0:
+        return
+    flattened_data = []
+    tree_spec = None
+    for d in data:
+        elems, tree_spec = tree_flatten(d)
+        flattened_data.append(elems)
+    merged_data = []
+    for elem_batch in zip(*flattened_data):
+        if isinstance(elem_batch[0], torch.Tensor):
+            merged_data.append(torch.cat(elem_batch, dim=0))
+        else:
+            merged_data.append(list(elem_batch))
+    return tree_unflatten(merged_data, tree_spec)