[shardformer] support interleaved pipeline (#4448)

* support interleaved pipeline

* fix unit test

* remove virtual stage test in stage mgr

* add droped type hint and updated bwd

colossalai/cluster/process_group_mesh.py

@@ -94,17 +94,23 @@ class ProcessGroupMesh:
         return np.unravel_index(rank, shape)
 
     @staticmethod
-    def ravel(coord: Tuple[int, ...], shape: Tuple[int, ...]) -> int:
+    def ravel(coord: Tuple[int, ...], shape: Tuple[int, ...], mode: str = 'raise') -> int:
         """Convert a coordinate to a rank.
+           mode: ['raise', 'wrap', 'clip'], see https://numpy.org/doc/stable/reference/generated/numpy.ravel_multi_index.html.
+           with wrap, index out of range would be wrapped around.
+           For instance, ravel((0, i, 0), (1, 2, 1), 'wrap') returns (i % 2)
 
         Args:
             coords (Tuple[int, ...]): Coordinate to be converted.
             shape (Tuple[int, ...]): Shape of the process group mesh.
+            mode (Optional[str]): The mode for numpy.ravel_multi_index.
 
         Returns:
             int: Rank of the coordinate.
         """
-        return np.ravel_multi_index(coord, shape)
+
+        assert mode in ["raise", "wrap", "clip"]
+        return np.ravel_multi_index(coord, shape, mode)
 
     def get_group(self, ranks_in_group: List[int], backend: Optional[str] = None) -> ProcessGroup:
         """Get the process group with the given ranks. It the process group doesn't exist, it will be created.

colossalai/pipeline/p2p.py

@@ -173,14 +173,10 @@ class PipelineP2PCommunication:
         Returns:
             Any: The input tensor or input tensor list.
         """
-        if self.stage_manager.is_first_stage():
-            input_tensor = None
-        else:
         if prev_rank is None:
             prev_rank = self.stage_manager.get_prev_rank()
         cur_rank = self.stage_manager.get_rank()
-            input_tensor = _recv_object(prev_rank, cur_rank,
-                                        self.stage_manager.get_p2p_process_group(prev_rank, cur_rank))
+        input_tensor = _recv_object(prev_rank, cur_rank, self.stage_manager.get_p2p_process_group(prev_rank, cur_rank))
 
         return input_tensor
 
@@ -193,9 +189,6 @@ class PipelineP2PCommunication:
         Returns:
             Any: The input gradient tensor or gradient tensor list.
         """
-        if self.stage_manager.is_last_stage():
-            output_tensor_grad = None
-        else:
         if next_rank is None:
             next_rank = self.stage_manager.get_next_rank()
         cur_rank = self.stage_manager.get_rank()
@@ -211,12 +204,10 @@ class PipelineP2PCommunication:
             output_object (Any): Object to be sent.
             next_rank (int, optional): The rank of the recipient of the tensor.
         """
-        if not self.stage_manager.is_last_stage():
         if next_rank is None:
             next_rank = self.stage_manager.get_next_rank()
         cur_rank = self.stage_manager.get_rank()
-            _send_object(output_object, cur_rank, next_rank,
-                         self.stage_manager.get_p2p_process_group(cur_rank, next_rank))
+        _send_object(output_object, cur_rank, next_rank, self.stage_manager.get_p2p_process_group(cur_rank, next_rank))
 
     def send_backward(self, input_object: Any, prev_rank: int = None) -> None:
         """Sends the gradient tensor to the previous stage in pipeline.
@@ -225,9 +216,7 @@ class PipelineP2PCommunication:
             input_object (Any): Object to be sent.
             prev_rank (int, optional): The rank of the recipient of the tensor
         """
-        if not self.stage_manager.is_first_stage():
         if prev_rank is None:
             prev_rank = self.stage_manager.get_prev_rank()
         cur_rank = self.stage_manager.get_rank()
-            _send_object(input_object, cur_rank, prev_rank,
-                         self.stage_manager.get_p2p_process_group(cur_rank, prev_rank))
+        _send_object(input_object, cur_rank, prev_rank, self.stage_manager.get_p2p_process_group(cur_rank, prev_rank))

colossalai/pipeline/schedule/interleaved_pp.py

+from functools import partial
+from typing import Any, Callable, Iterable, List, Optional, Union
+
+import torch
+import torch.cuda
+from torch.nn import Module
+from torch.utils._pytree import tree_map
+
+from colossalai.interface import OptimizerWrapper
+from colossalai.pipeline.p2p import PipelineP2PCommunication
+from colossalai.pipeline.stage_manager import PipelineStageManager
+from colossalai.utils.cuda import get_current_device
+
+from ._utils import detach, get_batch_size, get_micro_batch, merge_batch, model_forward, retain_grad, to_device
+from .base import PipelineSchedule
+
+
+class InterleavedSchedule(PipelineSchedule):
+
+    def __init__(self, num_microbatches: int, num_model_chunks: int, stage_manager: PipelineStageManager) -> None:
+        self.num_model_chunks = num_model_chunks
+        assert num_microbatches % self.num_model_chunks == 0, \
+            "Number of microbatches should be an integer multiple of number of model chunks"
+        super().__init__(stage_manager)
+        self.comm = PipelineP2PCommunication(stage_manager)
+        self.num_microbatches = num_microbatches
+        self.batch: Optional[Any] = None
+        self.batch_size: Optional[int] = None
+        self.microbatch_offset: Optional[int] = None
+        self.microbatch_size: Optional[int] = None
+
+    def load_batch(self, data_iter: Iterable, device: Optional[torch.device] = None) -> None:
+        """Load a batch from data iterator.
+
+        Args:
+            data_iter (Iterable): Data iterator.
+            device (Optional[torch.device], optional): Target device. Defaults to None.
+        """
+        batch = next(data_iter)
+        if device is not None:
+            batch = tree_map(partial(to_device, device=device), batch)
+        self.batch = batch
+        self.batch_size = get_batch_size(batch)
+        self.microbatch_offset = [0 for _ in range(self.num_model_chunks)]
+        assert self.batch_size % self.num_microbatches == 0, \
+            "Batch size should divided by the number of microbatches"
+        self.microbatch_size = self.batch_size // self.num_microbatches
+
+    def load_micro_batch(self, model_chunk_id: int) -> Any:
+        """Load a micro batch from the current batch.
+
+        Args:
+            microbatch_id (int): the current model chunk idx.
+
+        Returns:
+            Any: Micro batch.
+        """
+        micro_batch = get_micro_batch(self.batch, self.microbatch_offset[model_chunk_id], self.microbatch_size)
+        self.microbatch_offset[model_chunk_id] += self.microbatch_size
+        return tree_map(partial(to_device, device=get_current_device()), micro_batch)
+
+    def get_model_chunk_id(self, microbatch_id: int, forward: bool) -> int:
+        """Helper method to get the model chunk ID given the iteration number.
+
+        Args:
+            microbatch_id (int): the current microbatch idx
+            forward (bool): if is the forward process
+
+        Returns:
+            int: The model chunk idx of the input microbatch_id
+        """
+        microbatch_id_in_group = (microbatch_id) % (self.stage_manager.num_stages * self.num_model_chunks)
+        model_chunk_id = microbatch_id_in_group // self.stage_manager.num_stages
+        if not forward:
+            model_chunk_id = (self.num_model_chunks - model_chunk_id - 1)
+        return model_chunk_id
+
+    def is_first_stage(self, model_chunk_id: int) -> bool:
+        """Is the current virtual stage the first stage
+
+        Args:
+            model_chunk_id (int): The current model chunk idx.
+
+        Returns:
+            bool: Whether the current virtual stage is the first stage.
+        """
+        if self.stage_manager.is_first_stage() and model_chunk_id == 0:
+            return True
+        return False
+
+    def is_last_stage(self, model_chunk_id: int) -> bool:
+        """Is the current virtual stage the last stage
+
+        Args:
+            model_chunk_id (int): The current model chunk idx.
+
+        Returns:
+            bool: Whether the current virtual stage is the last stage.
+        """
+        if self.stage_manager.is_last_stage() and model_chunk_id == self.num_model_chunks - 1:
+            return True
+        return False
+
+    def recv_forward(self, model_chunk_id: int, prev_rank: int = None) -> Any:
+        """Copy the forward output from the previous stage in pipeline as the input tensor of this stage.
+           For interleaved 1F1B.
+
+        Args:
+            model_chunk_id (int): The current model chunk idx.
+            prev_rank (int, optional): The rank of the source of the tensor.
+
+        Returns:
+            Any: The input tensor or input tensor list.
+        """
+        if self.is_first_stage(model_chunk_id):
+            input_tensor = None
+        else:
+            input_tensor = self.comm.recv_forward(prev_rank)
+
+        return input_tensor
+
+    def recv_backward(self, model_chunk_id: int, next_rank: int = None) -> Any:
+        """Copy the gradient tensor from the next stage in pipeline as the input gradient of this stage.
+           For interleaved 1F1B.
+
+        Args:
+            model_chunk_id (int): The current model chunk idx.
+            next_rank (int, optional): The rank of the source of the tensor.
+
+        Returns:
+            Any: The input gradient tensor or gradient tensor list.
+        """
+        if self.is_last_stage(model_chunk_id):
+            output_tensor_grad = None
+        else:
+            output_tensor_grad = self.comm.recv_backward(next_rank)
+
+        return output_tensor_grad
+
+    def send_forward(self, model_chunk_id, output_object: Any, next_rank: int = None) -> None:
+        """Sends the input tensor to the next stage in pipeline.
+           For interleaved 1F1B.
+
+        Args:
+            model_chunk_id (int): The current model chunk idx.
+            output_object (Any): Object to be sent.
+            next_rank (int, optional): The rank of the recipient of the tensor.
+        """
+        if not self.is_last_stage(model_chunk_id):
+            self.comm.send_forward(output_object, next_rank)
+
+    def send_backward(self, model_chunk_id, input_object: Any, prev_rank: int = None) -> None:
+        """Sends the gradient tensor to the previous stage in pipeline.
+           For interleaved 1F1B.
+
+        Args:
+            model_chunk_id (int): The current model chunk idx.
+            input_object (Any): Object to be sent.
+            prev_rank (int, optional): The rank of the recipient of the tensor
+        """
+        if not self.is_first_stage(model_chunk_id):
+            self.comm.send_backward(input_object, prev_rank)
+
+    def forward_step(self,
+                     model_chunk: Module,
+                     model_chunk_id: int,
+                     input_obj: Optional[dict],
+                     criterion: Callable,
+                     accum_loss: Optional[torch.Tensor] = None,
+                     outputs: Optional[List[Any]] = None) -> Union[torch.Tensor, dict]:
+        """Forward one step of the pipeline
+        Args:
+            model (Module): Model Chunk to be run
+            input_obj (Optional[dict]): The output from the previous stage. If it is the first stage, the `input_obj` is None.
+            criterion (Callable): Criterion to calculate loss.
+            accum_loss (Optional[torch.Tensor], optional): Accumulated loss. Defaults to None.
+            outputs (Optional[List[Any]], optional): List to store the output of the last stage (final output). Defaults to None.
+
+        Returns:
+            Union[torch.Tensor, dict]: The intermediate output (dict) of the current stage. If it is the last stage, the output is the loss (Tensor).
+        """
+        micro_batch = self.load_micro_batch(model_chunk_id=model_chunk_id)
+
+        # for the first stage, input_obj is None
+        # for the non-first stage, input_obj is the output of the previous stage and it's must be a dict
+        output_obj = model_forward(model_chunk[model_chunk_id], micro_batch, input_obj)
+
+        if self.is_last_stage(model_chunk_id):
+            loss = criterion(output_obj, micro_batch) / self.num_microbatches
+            if accum_loss is not None:
+                accum_loss.add_(loss.detach())
+            if outputs is not None:
+                outputs.append(tree_map(detach, output_obj))
+            return loss
+        else:
+            return output_obj
+
+    def backward_step(self, optimizer: OptimizerWrapper, input_obj: Optional[dict],
+                      output_obj: Union[dict, torch.Tensor], output_obj_grad: Optional[dict]) -> Optional[dict]:
+        """Backward one step of the pipeline
+
+        Args:
+            optimizer (OptimizerWrapper): Optimizer to update the model
+            input_obj (Optional[dict]): Output of the previous stage. If it is the first stage, the `input_obj` is None.
+            output_obj (Union[dict, torch.Tensor]): Output of the current stage. If it is the last stage, the output is the loss (Tensor).
+            output_obj_grad (dict): Gradient of the `output_obj`. If it is the last stage, the `output_obj_grad` is None.
+
+        Returns:
+            Optional[dict]: Gradient of the `input_obj`. If it is the first stage, the `input_obj_grad` is None.
+        """
+
+        # Retain the grad on the input_obj.
+        tree_map(retain_grad, input_obj)
+
+        # Backward pass.
+        if output_obj_grad is None:
+            optimizer.backward(output_obj)
+        else:
+            if "backward_tensor_keys" not in output_obj:
+                for k, grad in output_obj_grad.items():
+                    optimizer.backward_by_grad(output_obj[k], grad)
+            else:
+                for k, grad in output_obj_grad.items():
+                    output_obj[k].grad = grad
+                for k in output_obj["backward_tensor_keys"]:
+                    tensor_to_backward = output_obj[k]
+                    optimizer.backward_by_grad(tensor_to_backward, tensor_to_backward.grad)
+
+        # Collect the grad of the input_obj.
+        input_obj_grad = None
+        if input_obj is not None:
+            input_obj_grad = {}
+            for k, v in input_obj.items():
+                if isinstance(v, torch.Tensor) and v.grad is not None:
+                    input_obj_grad[k] = v.grad
+        return input_obj_grad
+
+    def forward_backward_step(self,
+                              model_chunk: Module,
+                              optimizer: OptimizerWrapper,
+                              data_iter: Iterable,
+                              criterion: Callable[..., Any],
+                              return_loss: bool = False,
+                              return_outputs: bool = False) -> dict:
+        """Runs interleaved 1F1B schedule, with communication between pipeline stages.
+
+        Args:
+            model_chunk (List[Module]): Model Chunk to be trained.
+            optimizer (OptimizerWrapper): Optimizer to be used.
+            data_iter (Iterable): Data iterator.
+            criterion (Callable[[Any, Any], Tensor]): Criterion to be used. It should take two arguments: model outputs and inputs, and returns loss tensor.
+            return_loss (bool, optional): Whether to return loss. Defaults to False. Whether to return loss.
+            return_outputs (bool, optional): Whether to return model outputs. Defaults to False. Whether to return model outputs.
+
+        Returns:
+            dict: A dict with keys: 'loss' and 'outputs'.
+        """
+        forward_only = not torch.is_grad_enabled()
+
+        self.load_batch(data_iter)
+        num_model_chunks = len(model_chunk)
+
+        # num_warmup_microbatches is the step when not all the processes are working
+        num_microbatches = self.num_microbatches * num_model_chunks
+        if forward_only:
+            num_warmup_microbatches = num_microbatches
+        else:
+            num_warmup_microbatches = (self.stage_manager.num_stages - self.stage_manager.stage - 1) * 2
+            num_warmup_microbatches += (num_model_chunks - 1) * self.stage_manager.num_stages
+            num_warmup_microbatches = min(num_warmup_microbatches, num_microbatches)
+
+        num_microbatches_remaining = num_microbatches - num_warmup_microbatches
+
+        # Input, output tensors only need to be saved when doing backward passes
+        input_objs = None
+        output_objs = None
+
+        if not forward_only:
+            input_objs = [[] for _ in range(num_model_chunks)]
+            output_objs = [[] for _ in range(num_model_chunks)]
+
+        outputs = [] if return_outputs and self.stage_manager.is_last_stage() else None
+
+        if return_loss and self.stage_manager.is_last_stage():
+            accum_loss = torch.zeros(1, device=get_current_device())
+        else:
+            accum_loss = None
+
+        # for ranks except the first one, get into recv state
+        # print(self.stage_manager.stage,num_microbatches, num_warmup_microbatches, num_microbatches_remaining)
+        input_obj = self.recv_forward(0)
+        input_objs[0].append(input_obj)
+        # Run warmup forward passes.
+        for i in range(num_warmup_microbatches):
+            model_chunk_id = self.get_model_chunk_id(i, forward=True)
+
+            # recv first on first rank to avoid sending or recving at the same time
+            if self.stage_manager.is_first_stage():
+                input_obj = self.recv_forward(model_chunk_id)
+                output_obj = self.forward_step(model_chunk, model_chunk_id, input_obj, criterion, accum_loss, outputs)
+                self.send_forward(model_chunk_id, output_obj)
+                if not forward_only:
+                    input_objs[model_chunk_id].append(input_obj)
+                    output_objs[model_chunk_id].append(output_obj)
+            else:
+                output_obj = self.forward_step(model_chunk, model_chunk_id, input_obj, criterion, accum_loss, outputs)
+                if not forward_only:
+                    output_objs[model_chunk_id].append(output_obj)
+                self.send_forward(model_chunk_id, output_obj)
+                if num_microbatches_remaining == 0 and i + 1 == num_warmup_microbatches:
+                    break
+                else:
+                    model_chunk_id = self.get_model_chunk_id(i + 1, forward=True)
+
+                    input_obj = self.recv_forward(model_chunk_id)
+                    if not forward_only:
+                        input_objs[model_chunk_id].append(input_obj)
+
+        # Run 1F1B in steady state.
+        for i in range(num_microbatches_remaining):
+            model_chunk_id = self.get_model_chunk_id(i + num_warmup_microbatches, forward=True)
+            last_iteration = (i == (num_microbatches_remaining - 1))
+
+            output_obj = self.forward_step(model_chunk, model_chunk_id, input_obj, criterion, accum_loss, outputs)
+            if forward_only:
+                self.send_forward(model_chunk_id, output_obj)
+
+                if not last_iteration:
+                    input_obj = self.recv_forward(model_chunk_id)
+
+            else:
+                self.send_forward(model_chunk_id, output_obj)
+                # Add input_obj and output_obj to end of list.
+                input_objs[model_chunk_id].append(input_obj)
+                output_objs[model_chunk_id].append(output_obj)
+
+                model_chunk_id = self.get_model_chunk_id(i, forward=False)
+                output_obj_grad = self.recv_backward(model_chunk_id)
+
+                # Pop output_obj and output_obj from the start of the list for
+                # the backward pass.
+                input_obj = input_objs[model_chunk_id].pop(0)
+                output_obj = output_objs[model_chunk_id].pop(0)
+
+                # backward
+                input_obj_grad = self.backward_step(optimizer, input_obj, output_obj, output_obj_grad)
+
+                if last_iteration:
+                    input_obj = None
+                else:
+                    model_chunk_id = self.get_model_chunk_id(i + num_warmup_microbatches + 1, forward=True)
+                    input_obj = self.recv_forward(model_chunk_id)
+                model_chunk_id = self.get_model_chunk_id(i, forward=False)
+                self.send_backward(model_chunk_id, input_obj_grad)
+
+        # Run cooldown backward passes.
+        if not forward_only:
+            for i in range(num_microbatches_remaining, num_microbatches):
+                model_chunk_id = self.get_model_chunk_id(i, forward=False)
+                # print(f"{self.stage_manager.stage}/{model_chunk_id}: {len(input_objs[model_chunk_id])} {len(output_objs[model_chunk_id])} {i}")
+                input_obj = input_objs[model_chunk_id].pop(0)
+                output_obj = output_objs[model_chunk_id].pop(0)
+
+                output_obj_grad = self.recv_backward(model_chunk_id)
+                input_obj_grad = self.backward_step(optimizer, input_obj, output_obj, output_obj_grad)
+                self.send_backward(model_chunk_id, input_obj_grad)
+
+        if outputs is not None:
+            outputs = merge_batch(outputs)
+        return {'loss': accum_loss, 'outputs': outputs}

colossalai/pipeline/schedule/one_f_one_b.py

@@ -53,6 +53,62 @@ class OneForwardOneBackwardSchedule(PipelineSchedule):
         self.microbatch_offset += self.microbatch_size
         return tree_map(partial(to_device, device=get_current_device()), micro_batch)
 
+    def recv_forward(self, prev_rank: int = None) -> Any:
+        """Copy the forward output from the previous stage in pipeline as the input tensor of this stage.
+           For 1F1B.
+
+        Args:
+            prev_rank (int, optional): The rank of the source of the tensor.
+
+        Returns:
+            Any: The input tensor or input tensor list.
+        """
+        if self.stage_manager.is_first_stage():
+            input_tensor = None
+        else:
+            input_tensor = self.comm.recv_forward(prev_rank)
+
+        return input_tensor
+
+    def recv_backward(self, next_rank: int = None) -> Any:
+        """Copy the gradient tensor from the next stage in pipeline as the input gradient of this stage.
+           For 1F1B.
+
+        Args:
+            next_rank (int, optional): The rank of the source of the tensor.
+
+        Returns:
+            Any: The input gradient tensor or gradient tensor list.
+        """
+        if self.stage_manager.is_last_stage():
+            output_tensor_grad = None
+        else:
+            output_tensor_grad = self.comm.recv_backward(next_rank)
+
+        return output_tensor_grad
+
+    def send_forward(self, output_object: Any, next_rank: int = None) -> None:
+        """Sends the input tensor to the next stage in pipeline.
+           For 1F1B.
+
+        Args:
+            output_object (Any): Object to be sent.
+            next_rank (int, optional): The rank of the recipient of the tensor.
+        """
+        if not self.stage_manager.is_last_stage():
+            self.comm.send_forward(output_object, next_rank)
+
+    def send_backward(self, input_object: Any, prev_rank: int = None) -> None:
+        """Sends the gradient tensor to the previous stage in pipeline.
+           For 1F1B.
+
+        Args:
+            input_object (Any): Object to be sent.
+            prev_rank (int, optional): The rank of the recipient of the tensor
+        """
+        if not self.stage_manager.is_first_stage():
+            self.comm.send_backward(input_object, prev_rank)
+
     def forward_step(self,
                      model: Module,
                      input_obj: Optional[dict],
@@ -171,11 +227,11 @@ class OneForwardOneBackwardSchedule(PipelineSchedule):
 
         # Run warmup forward passes.
         for i in range(num_warmup_microbatches):
-            input_obj = self.comm.recv_forward()
+            input_obj = self.recv_forward()
 
             output_obj = self.forward_step(model, input_obj, criterion, accum_loss, outputs)
 
-            self.comm.send_forward(output_obj)
+            self.send_forward(output_obj)
 
             if not forward_only:
                 input_objs.append(input_obj)
@@ -185,7 +241,7 @@ class OneForwardOneBackwardSchedule(PipelineSchedule):
         # If all microbatches are run in warmup / cooldown phase, then no need to
         # receive this tensor here.
         if num_microbatches_remaining > 0:
-            input_obj = self.comm.recv_forward()
+            input_obj = self.recv_forward()
 
         # Run 1F1B in steady state.
         for i in range(num_microbatches_remaining):
@@ -193,15 +249,15 @@ class OneForwardOneBackwardSchedule(PipelineSchedule):
 
             output_obj = self.forward_step(model, input_obj, criterion, accum_loss, outputs)
             if forward_only:
-                self.comm.send_forward(output_obj)
+                self.send_forward(output_obj)
 
                 if not last_iteration:
-                    input_obj = self.comm.recv_forward()
+                    input_obj = self.recv_forward()
 
             else:
                 # TODO adjust here
-                self.comm.send_forward(output_obj)
-                output_obj_grad = self.comm.recv_backward()
+                self.send_forward(output_obj)
+                output_obj_grad = self.recv_backward()
 
                 # Add input_obj and output_obj to end of list.
                 input_objs.append(input_obj)
@@ -216,8 +272,8 @@ class OneForwardOneBackwardSchedule(PipelineSchedule):
                 if last_iteration:
                     input_obj = None
                 else:
-                    input_obj = self.comm.recv_forward()
-                self.comm.send_backward(input_obj_grad)
+                    input_obj = self.recv_forward()
+                self.send_backward(input_obj_grad)
 
         # Run cooldown backward passes.
         if not forward_only:
@@ -225,9 +281,9 @@ class OneForwardOneBackwardSchedule(PipelineSchedule):
                 input_obj = input_objs.pop(0)
                 output_obj = output_objs.pop(0)
 
-                output_obj_grad = self.comm.recv_backward()
+                output_obj_grad = self.recv_backward()
                 input_obj_grad = self.backward_step(optimizer, input_obj, output_obj, output_obj_grad)
-                self.comm.send_backward(input_obj_grad)
+                self.send_backward(input_obj_grad)
 
         if outputs is not None:
             outputs = merge_batch(outputs)

colossalai/pipeline/stage_manager.py

@@ -17,28 +17,24 @@ class PipelineStageManager:
     Attributes:
         num_stages (int): Number of stages in the pipeline.
         stage (int): The current stage.
-        num_virtual_stages (int): Number of virtual stages in the pipeline.
-        virtual_stage (int): The current virtual stage.
     """
 
-    def __init__(self, pg_mesh: ProcessGroupMesh, pipeline_axis: int) -> None:
+    def __init__(self, pg_mesh: ProcessGroupMesh, pipeline_axis: int, is_virtual: bool = False) -> None:
         self.pg_mesh = pg_mesh
         self.pipeline_axis = pipeline_axis
-        self.num_virtual_stages: Optional[int] = None
-        self.virtual_stage: Optional[int] = None
         self.prev_rank: Optional[Tuple[int, ...]] = None
         self.next_rank: Optional[Tuple[int, ...]] = None
         self.p2p_groups: Dict[Tuple[int, int], ProcessGroup] = {}
         # init prev and next coord
         coord = self.pg_mesh.coordinate()
-        if self.stage > 0:
+        # the prev rank of rank0 is the last rank
         prev_coord = coord[: self.pipeline_axis] + \
             (coord[self.pipeline_axis] - 1,) + coord[self.pipeline_axis + 1:]
-            self.prev_rank = self.pg_mesh.ravel(prev_coord, self.pg_mesh.shape)
-        if self.stage < self.num_stages - 1:
+        self.prev_rank = self.pg_mesh.ravel(prev_coord, self.pg_mesh.shape, mode='wrap')
+        # the next rank of the last rank is rank0
         next_coord = coord[: self.pipeline_axis] + \
             (coord[self.pipeline_axis] + 1,) + coord[self.pipeline_axis + 1:]
-            self.next_rank = self.pg_mesh.ravel(next_coord, self.pg_mesh.shape)
+        self.next_rank = self.pg_mesh.ravel(next_coord, self.pg_mesh.shape, mode='wrap')
 
         # init p2p process groups
         stages = list(range(self.num_stages))
@@ -48,32 +44,28 @@ class PipelineStageManager:
                 ranks_in_group = self.pg_mesh.get_ranks_in_group(group)
                 self.p2p_groups[tuple(ranks_in_group)] = group
 
-    def is_first_stage(self, virtual: bool = False) -> bool:
-        """Is the current stage the first stage.
+        if is_virtual:
+            # add the process group of the first rank and the last rank
+            # only used in interleaved pipeline for now
+            group = self.pg_mesh.get_group_along_axis(self.pipeline_axis, [stages[0], stages[-1]])
+            if self.stage in [stages[0], stages[-1]]:
+                ranks_in_group = self.pg_mesh.get_ranks_in_group(group)
+                self.p2p_groups[tuple(ranks_in_group)] = group
 
-        Args:
-            virtual (bool, optional): Whether to consider virtual stages. Defaults to False.
+    def is_first_stage(self) -> bool:
+        """Is the current stage the first stage.
 
         Returns:
             bool: Whether the current stage is the first stage.
         """
-        if virtual:
-            assert self.num_virtual_stages is not None
-            return self.virtual_stage == 0
         return self.stage == 0
 
-    def is_last_stage(self, virtual: bool = False) -> bool:
+    def is_last_stage(self) -> bool:
         """Is the current stage the last stage.
 
-        Args:
-            virtual (bool, optional): Whether to consider virtual stages. Defaults to False.
-
         Returns:
             bool: Whether the current stage is the last stage.
         """
-        if virtual:
-            assert self.num_virtual_stages is not None
-            return self.virtual_stage == self.num_virtual_stages - 1
         return self.stage == self.num_stages - 1
 
     @property
@@ -108,7 +100,6 @@ class PipelineStageManager:
         Returns:
             int: Rank of the previous stage.
         """
-        assert not self.is_first_stage(), "Cannot get previous rank in the first stage."
         return self.prev_rank
 
     def get_next_rank(self) -> int:
@@ -117,39 +108,8 @@ class PipelineStageManager:
         Returns:
             int: Rank of the next stage.
         """
-        assert not self.is_last_stage(), "Cannot get next rank in the last stage."
         return self.next_rank
 
-    def set_num_virtual_stages(self, num_virtual_stages: int) -> None:
-        """Set the number of virtual stages.
-
-        Args:
-            num_virtual_stages (int): Number of virtual stages.
-        """
-        self.num_virtual_stages = num_virtual_stages
-
-    def set_virtual_stage(self, virtual_stage: int) -> None:
-        """Set the virtual stage.
-
-        Args:
-            virtual_stage (int): Virtual stage.
-        """
-        self.virtual_stage = virtual_stage
-
-    @contextmanager
-    def switch_virtual_stage(self, virtual_stage: int) -> None:
-        """A context manager to switch virtual stage.
-
-        Args:
-            virtual_stage (int): Target virtual stage.
-        """
-        old_stage = self.virtual_stage
-        try:
-            self.set_virtual_stage(virtual_stage)
-            yield
-        finally:
-            self.set_virtual_stage(old_stage)
-
     def get_p2p_process_group(self, first_rank: int, second_rank: int) -> ProcessGroup:
         """Get the p2p process group between two ranks. The order of the two ranks does not matter.
 

tests/test_pipeline/test_schedule/test_interleaved.py

+import copy
+from functools import partial
+from types import MethodType
+
+import pytest
+import torch
+import torch.nn as nn
+
+import colossalai
+from colossalai.cluster import ProcessGroupMesh
+from colossalai.interface import OptimizerWrapper
+from colossalai.pipeline.schedule.interleaved_pp import InterleavedSchedule
+from colossalai.pipeline.stage_manager import PipelineStageManager
+from colossalai.testing import parameterize, rerun_if_address_is_in_use, spawn
+from colossalai.testing.random import seed_all
+
+
+class MlpModel(nn.Module):
+
+    def __init__(self):
+        super(MlpModel, self).__init__()
+        self.linear1 = nn.Linear(4, 8)
+        self.linear2 = nn.Linear(8, 8)
+        self.linear3 = nn.Linear(8, 8)
+        self.linear4 = nn.Linear(8, 8)
+        self.linear5 = nn.Linear(8, 8)
+        self.linear6 = nn.Linear(8, 8)
+        self.linear7 = nn.Linear(8, 8)
+        self.linear8 = nn.Linear(8, 4)
+
+    def forward(self, x):
+        x = self.linear1(x)
+        x = self.linear2(x)
+        x = self.linear3(x)
+        x = self.linear4(x)
+        x = self.linear5(x)
+        x = self.linear6(x)
+        x = self.linear7(x)
+        x = self.linear8(x)
+        return x
+
+
+def pp_linear_fwd(forward,
+                  data: torch.Tensor = None,
+                  input_obj: torch.Tensor = None,
+                  stage_mgr: PipelineStageManager = None,
+                  num_chunks: int = None,
+                  model_chunk_id: int = None):
+
+    if stage_mgr.is_first_stage() and model_chunk_id == 0:
+        return {'input_obj': forward(data)}
+    elif stage_mgr.is_last_stage() and model_chunk_id == num_chunks - 1:
+        return forward(input_obj)
+    else:
+        return {'input_obj': forward(input_obj)}
+
+
+@parameterize("num_micro_batches", [4, 8, 12])
+def examine_pp(num_micro_batches):
+    """
+    This test is to examine the correctness of interleaved 1F1B, compared with torch.
+    Be aware it contains some hardcodes.
+    """
+    world_size = torch.distributed.get_world_size()
+    local_rank = torch.distributed.get_rank()
+    seed_all(1453)
+
+    NUM_MICRO_BATCHS = num_micro_batches
+    BATCH_SIZE = num_micro_batches
+    NUM_CHUNKS = 2
+
+    # create model
+    torch_model = MlpModel().cuda()
+
+    pp_model = copy.deepcopy(torch_model).cuda()
+
+    DP_DIM, PP_DIM, TP_DIM = 0, 1, 2
+    pg_mesh = ProcessGroupMesh(1, world_size, 1)
+    stage_manager = PipelineStageManager(pg_mesh, PP_DIM, is_virtual=True)
+    schedule = InterleavedSchedule(NUM_MICRO_BATCHS, NUM_CHUNKS, stage_manager)
+
+    sharded_model = torch.nn.ModuleList()
+    for idx, (_, sub_model) in enumerate(pp_model.named_children()):
+        if idx % (world_size) == local_rank:
+            sub_model._forward = sub_model.forward
+            sub_model.forward = MethodType(
+                partial(pp_linear_fwd,
+                        stage_mgr=stage_manager,
+                        num_chunks=NUM_CHUNKS,
+                        model_chunk_id=len(sharded_model)), sub_model._forward)
+            sharded_model.append(sub_model.cuda())
+
+    # create optimizer
+    torch_optimizer = torch.optim.SGD(torch_model.parameters(), lr=1)
+    pp_optimizer = OptimizerWrapper(torch.optim.SGD(sharded_model.parameters(), lr=1))
+
+    # create
+    seed_all(1453)
+    if local_rank == 0:
+        input_list = [torch.rand(BATCH_SIZE, 4).cuda()]
+    else:
+        input_list = [torch.zeros(BATCH_SIZE, 4).cuda()]
+    torch.distributed.all_reduce(input_list[0])
+
+    criterion = lambda x, y: torch.mean(x)
+
+    # forward and backward
+    torch_output = torch_model(input_list[0])
+    torch_loss = criterion(torch_output, _)
+    torch_loss.backward()
+
+    pp_ret = schedule.forward_backward_step(sharded_model,
+                                            pp_optimizer,
+                                            iter(input_list),
+                                            criterion,
+                                            return_loss=True,
+                                            return_outputs=True)
+
+    # check loss
+    if stage_manager.is_last_stage():
+        assert torch.allclose(torch_loss, pp_ret['loss'])
+
+    # check gradients
+    torch_grad = []
+    for torch_p in torch_model.parameters():
+        torch_grad.append(torch_p.grad.data)
+
+    for idx, pp_p in enumerate(sharded_model.parameters()):
+        if idx < 2:
+            assert torch.allclose(torch_grad[idx + local_rank * 2], pp_p.grad.data)
+        else:
+            assert torch.allclose(torch_grad[idx + local_rank * 2 + 6], pp_p.grad.data)
+
+    # step
+    torch_optimizer.step()
+    pp_optimizer.step()
+
+    # check updated param
+    torch_param = []
+    for torch_p in torch_model.parameters():
+        torch_param.append(torch_p.data)
+    for idx, pp_p in enumerate(sharded_model.parameters()):
+        if idx < 2:
+            assert torch.allclose(torch_param[idx + local_rank * 2], pp_p.data)
+        else:
+            assert torch.allclose(torch_param[idx + local_rank * 2 + 6], pp_p.data)
+
+
+def run_dist(rank, world_size, port):
+    colossalai.launch(config=dict(), rank=rank, world_size=world_size, port=port, host='localhost')
+    examine_pp()
+
+
+@pytest.mark.dist
+@rerun_if_address_is_in_use()
+def test_pp():
+    spawn(run_dist, 4)
+
+
+if __name__ == '__main__':
+    test_pp()

tests/test_pipeline/test_stage_manager.py

@@ -49,15 +49,6 @@ def check_stage_manager():
         next_rank = ranks_in_group[ranks_in_group.index(rank) + 1]
         assert stage_manager.get_next_rank() == next_rank
 
-    # check virtual stage
-    stage_manager.set_num_virtual_stages(PP_SIZE * 2)
-    assert stage_manager.num_virtual_stages == PP_SIZE * 2
-    stage_manager.set_virtual_stage(stage_manager.stage * 2)
-    assert stage_manager.virtual_stage == stage_manager.stage * 2
-    with stage_manager.switch_virtual_stage(stage_manager.stage * 2 + 1):
-        assert stage_manager.virtual_stage == stage_manager.stage * 2 + 1
-    assert stage_manager.virtual_stage == stage_manager.stage * 2
-
     # check p2p groups
     for prev, cur in zip(ranks_in_group[:-1], ranks_in_group[1:]):
         if rank in [prev, cur]: