[pipeline/rpc] support interleaving | fix checkpoint bug | change logic when dispatch data in work_list to ensure steady 1F1B (#1483)

* support p2p communication with any type of object | pass test

* reconstruct pipeline schedule with p2p_v2.py(support communication with List[Any]) | pass test

* [engin/schedule] use p2p_v2 to recontruct pipeline_schedule

* [pipeline/rpc] implement a demo for PP with cuda rpc framework

* [pipeline/rpc] support interleaving | fix checkpoint bug | change logic when dispatch data in work_list to ensure steady 1F1B

colossalai/pipeline/rpc/PipelineBase.py

@@ -1,7 +1,7 @@
 import threading
 from enum import Enum
 from typing import List, Any, Tuple, Dict
-from abc import ABC, abstractmethod
+from abc import ABC
 
 import torch
 from torch import nn
@@ -18,9 +18,8 @@ use_color_debug = False
 use_progress = False
 
 # TODO:
-# 1. design a unique_key without node.name (Maybe I can use combination of microbatch_id and stage_id)
-# 2. use waiting list to contain the uncomplete WorkItem
-# 3. think about the representation of the order of args and kwargs
+# 1. replace world_size with other parameters
+# 2. adjust to args and kwargs
 
 
 def color_debug(text, prefix=' ', color='blue'):
@@ -126,33 +125,32 @@ class RemoteOptimizer:
 class Worker:
 
     def __init__(self,
-                 cur_rank_module: nn.Module,
-                 rank: int,
-                 world_size: int,
+                 module_partition: nn.Module,
+                 pp_rank: int,
+                 actual_stage_num: int,
                  num_microbatches: int,
                  max_outstanding: int,
                  device: str,
                  checkpoint: bool = False) -> None:
         super().__init__()
-        self.rank = rank
-        self.world_size = world_size
+        self.pp_rank = pp_rank
+        self.actual_stage_num = actual_stage_num
         self.num_microbatches = num_microbatches
         self.max_outstanding = max_outstanding
         self.outstanding = 0
         self.checkpoint = checkpoint
-
-        if device == 'cuda':
-            device = f'cuda:{rank}'
         self.device = device
 
         self.future_devices = None if device is None or device == 'cpu' else [device]
 
-        self.stage_to_worker_rref: Dict[int, PyRRef] = None
+        self.pp_rank_to_worker_rref: Dict[int, PyRRef] = None
         self.producer_stage_ids: List[int] = None
         self.consumer_stage_ids: List[int] = None
 
         # module
-        self.cur_rank_module = cur_rank_module.to(device)
+        self.module_partition = module_partition.to(device)
+
+        self.debug_list = [None] * num_microbatches
 
         self.microbatch_id_to_backward_cache: Dict[int, BackwardCache] = dict()
 
@@ -164,16 +162,16 @@ class Worker:
         self.work_list_condition_lock = threading.Condition(threading.Lock())
         self.output_list_condition_lock = threading.Condition(threading.Lock())
 
-        self.main_loop_thread = threading.Thread(target=self._work_loop, name=f'rank_{rank}', daemon=True)
+        self.main_loop_thread = threading.Thread(target=self._work_loop, name=f'rank_{pp_rank}', daemon=True)
         self.main_loop_thread.start()
 
     def _get_future_by_device(self):
         return torch.futures.Future(devices=None if self.device in (None, 'cpu') else [self.device])
 
-    def sync_global_worker_rrefs(self, stage_to_worker_rref: Dict[int, PyRRef]) -> None:
-        assert self.stage_to_worker_rref is None, f"in rank {self.rank}, worker has sync global workers rrefs"
-        assert stage_to_worker_rref is not None, "stage_to_workers must be a dict instead of None"
-        self.stage_to_worker_rref = stage_to_worker_rref
+    def sync_global_worker_rrefs(self, pp_rank_to_worker_rref: Dict[int, PyRRef]) -> None:
+        assert self.pp_rank_to_worker_rref is None, f"in rank {self.pp_rank}, worker has sync global workers rrefs"
+        assert pp_rank_to_worker_rref is not None, "stage_to_workers must be a dict instead of None"
+        self.pp_rank_to_worker_rref = pp_rank_to_worker_rref
 
     def get_output_by_key(self, key: UniqueKey) -> Any:
         with self.output_list_condition_lock:
@@ -183,7 +181,7 @@ class Worker:
             output_work_item = self.output_list[key]
 
         output = output_work_item.output.wait()
-        # color_debug(f'rank {self.rank}, output {type(output)}', 'get output', 'red')
+        # color_debug(f'rank {self.pp_rank}, output {type(output)}', 'get output', 'red')
         output_work_item.refcount += 1
 
         # all consumers have been satisfied, the work_item can be released
@@ -193,8 +191,13 @@ class Worker:
 
         return output
 
-    # just for first rank
-    # TODO : input is args kwargs
+    def get_parameters(self) -> List[torch.Tensor]:
+        return [p for p in self.module_partition.parameters()]
+
+    def get_parameter_gradients(self) -> List[torch.Tensor]:
+        return [p.grad for p in self.module_partition.parameters()]
+
+    # just for first pp_rank
     def set_input(self, microbatch_id: int, microbatch: Tuple[Any]):
         with self.work_list_condition_lock:
             assert self.consumer_stage_ids is not None
@@ -203,16 +206,15 @@ class Worker:
             output = self._get_future_by_device()
             args = [microbatch] if isinstance(microbatch, torch.Tensor) else microbatch
 
-            work_item = WorkItem(self.rank, Phase.FORWARD, args, {}, output, microbatch_id, None, self.num_microbatches,
-                                 consumer_num)
+            work_item = WorkItem(self.pp_rank, Phase.FORWARD, args, {}, output, microbatch_id, None,
+                                 self.num_microbatches, consumer_num)
             self.work_list[key] = work_item
 
-            color_debug(f'rank {self.rank} receive data from dataloader', 'data dispatch', 'magenta')
+            color_debug(f'rank {self.pp_rank} receive data from dataloader', 'data dispatch', 'magenta')
 
             self.work_list_condition_lock.notify_all()
 
-    # just for last rank
-    # TODO : write a function to add gradient to work_list and see if there is contradictory
+    # just for last pp_rank
     def _begin_backward(self, microbatch_id: int):
         with self.work_list_condition_lock:
             assert self.producer_stage_ids is not None
@@ -221,10 +223,10 @@ class Worker:
             output = self._get_future_by_device()
             grad_wrt_loss = torch.tensor(1, device=self.device)
 
-            work_item = WorkItem(self.rank, Phase.BACKWARD, grad_wrt_loss, {}, output, microbatch_id, None,
+            work_item = WorkItem(self.pp_rank, Phase.BACKWARD, grad_wrt_loss, {}, output, microbatch_id, None,
                                  self.num_microbatches, producer_num)
 
-            color_debug(f'rank {self.rank} propose backward', 'data dispatch', 'magenta')
+            color_debug(f'rank {self.pp_rank} propose backward', 'data dispatch', 'magenta')
 
             self.work_list[key] = work_item
             self.work_list_condition_lock.notify_all()
@@ -238,7 +240,7 @@ class Worker:
         consumer_num = len(self.consumer_stage_ids)
         assert producer_num > 0, "only stage that has producers can subscribe producers"
 
-        stage_id = self.rank
+        stage_id = self.pp_rank
 
         subscribe_forward_futures: List[Future] = [None] * producer_num
         output = self._get_future_by_device()
@@ -246,10 +248,10 @@ class Worker:
         for i in range(producer_num):
             producer_stage_id = self.producer_stage_ids[i]
             producer_output_key = UniqueKey(microbatch_id, Phase.FORWARD)
-            producer_worker_rref = self.stage_to_worker_rref[producer_stage_id]
+            producer_worker_rref = self.pp_rank_to_worker_rref[producer_stage_id]
             subscribe_forward_futures[i] = producer_worker_rref.rpc_async().get_output_by_key(producer_output_key)
 
-        color_debug(f'rank {self.rank} get {len(subscribe_forward_futures)} futs from its producer', 'data dispatch',
+        color_debug(f'rank {self.pp_rank} get {len(subscribe_forward_futures)} futs from its producer', 'data dispatch',
                     'magenta')
 
         args = []
@@ -261,14 +263,14 @@ class Worker:
         work_item_from_producer = WorkItem(stage_id, Phase.FORWARD, args, {}, output, microbatch_id, None,
                                            self.num_microbatches, consumer_num)
 
-        color_debug(f'rank {self.rank} get value {tensor_shape_list(args)} from fut', 'data dispatch', 'magenta')
+        color_debug(f'rank {self.pp_rank} get value {tensor_shape_list(args)} from fut', 'data dispatch', 'magenta')
         # add work_item to work_list
         with self.work_list_condition_lock:
             key = UniqueKey(microbatch_id, Phase.FORWARD)
             assert key not in self.work_list
             self.work_list[key] = work_item_from_producer
             color_debug(
-                f'rank_{self.rank} load a new task to its work_list {key} {work_item_from_producer.phase} data: {tensor_shape_list(work_item_from_producer.args)}',
+                f'rank_{self.pp_rank} load a new task to its work_list {key} {work_item_from_producer.phase} data: {tensor_shape_list(work_item_from_producer.args)}',
                 'data dispatch', 'magenta')
             self.work_list_condition_lock.notify_all()
 
@@ -282,18 +284,18 @@ class Worker:
         assert consumer_num > 0, "only stage that has consumers can subscribe comsumers"
 
         # TODO : is this right?
-        stage_id = self.rank
+        stage_id = self.pp_rank
 
         subscribe_backward_futures: List[Future] = [None] * consumer_num
         output = self._get_future_by_device()
 
-        color_debug(f'rank {self.rank} get {len(subscribe_backward_futures)} futs from its consumer', 'data dispatch',
-                    'magenta')
+        color_debug(f'rank {self.pp_rank} get {len(subscribe_backward_futures)} futs from its consumer',
+                    'data dispatch', 'magenta')
 
         for i in range(consumer_num):
             consumer_stage_id = self.consumer_stage_ids[i]
             consumer_output_key = UniqueKey(microbatch_id, Phase.BACKWARD)
-            consumer_worker_rref = self.stage_to_worker_rref[consumer_stage_id]
+            consumer_worker_rref = self.pp_rank_to_worker_rref[consumer_stage_id]
             subscribe_backward_futures[i] = consumer_worker_rref.rpc_async().get_output_by_key(consumer_output_key)
 
         args = []
@@ -305,7 +307,7 @@ class Worker:
         work_item_from_consumer = WorkItem(stage_id, Phase.BACKWARD, args, {}, output, microbatch_id, None,
                                            self.num_microbatches, producer_num)
 
-        color_debug(f'rank {self.rank} get value {tensor_shape_list(args)} from fut', 'data dispatch', 'magenta')
+        color_debug(f'rank {self.pp_rank} get value {tensor_shape_list(args)} from fut', 'data dispatch', 'magenta')
 
         # add work_item to work_list
         with self.work_list_condition_lock:
@@ -313,13 +315,12 @@ class Worker:
             assert key not in self.work_list
             self.work_list[key] = work_item_from_consumer
             color_debug(
-                f'rank_{self.rank} load a new task to its work_list {key} {work_item_from_consumer.phase} data: {tensor_shape_list(work_item_from_consumer.args)}',
+                f'rank_{self.pp_rank} load a new task to its work_list {key} {work_item_from_consumer.phase} data: {tensor_shape_list(work_item_from_consumer.args)}',
                 'data dispatch', 'magenta')
             self.work_list_condition_lock.notify_all()
 
-    # TODO : fit in any type of partition of network
     def _get_producer_consumer(self) -> None:
-        rank = self.rank
+        rank = self.pp_rank
         assert self.producer_stage_ids is None, f"all the producers of rank {rank} has been subscribed"
         assert self.consumer_stage_ids is None, f"all the consumers of rank {rank} has been subscribed"
 
@@ -332,34 +333,41 @@ class Worker:
         next_rank = rank + 1
         if prev_rank >= 0:
             self.producer_stage_ids.append(prev_rank)
-        if next_rank <= self.world_size - 1:
+        if next_rank <= self.actual_stage_num - 1:
             self.consumer_stage_ids.append(next_rank)
 
-    def _skip_forward(self, work_item_phase: Phase) -> bool:
-        if work_item_phase == Phase.FORWARD and \
-            self.max_outstanding is not None and \
-            self.outstanding >= self.max_outstanding:
-            return True
-        return False
-
     def _get_work_item_key(self) -> UniqueKey:
         with self.work_list_condition_lock:
             while len(self.work_list) == 0:
                 self.work_list_condition_lock.wait()
 
             # execute backward first (if backward phase in work_list)
-
             select_work_list_key = None
             for key in self.work_list:
                 work_item = self.work_list[key]
-
-                if work_item.phase == Phase.BACKWARD:
-                    return key
-
-                if self._skip_forward(work_item.phase):
+                if work_item.phase == Phase.FORWARD and \
+                    self.max_outstanding is not None and \
+                    self.outstanding >= self.max_outstanding:
                     continue
                 else:
-                    select_work_list_key = key
+                    if select_work_list_key is not None and \
+                        select_work_list_key.phase == Phase.FORWARD and \
+                        key.phase == Phase.BACKWARD:
+                        continue
+
+                    if select_work_list_key is None:
+                        select_work_list_key = key
+                    else:
+                        phase_pair = (select_work_list_key.phase, key.phase)
+                        # choose forward first
+                        if phase_pair == (Phase.BACKWARD, Phase.FORWARD):
+                            select_work_list_key = key
+                        elif phase_pair == (Phase.FORWARD, Phase.BACKWARD):
+                            continue
+                        # choose work_item which has a smaller microbactch_id first
+                        elif key.microbatch_id < select_work_list_key.microbatch_id:
+                            select_work_list_key = key
+
         return select_work_list_key
 
     def _consume_work_item_by_phase(self, work_item: WorkItem):
@@ -369,7 +377,10 @@ class Worker:
         microbatch_id = work_item.microbatch_id
         consume_result = None
 
-        # color_debug(f'rank_{self.rank} enter consume', 'consume', 'blue')
+        # if self.pp_rank == 0:
+        #     print(f"I am rank_{self.pp_rank} microbatch_id : {microbatch_id}", work_item.phase, len(self.work_list))
+
+        # color_debug(f'rank_{self.pp_rank} enter consume', 'consume', 'blue')
 
         if phase == Phase.FORWARD:
             self.outstanding += 1
@@ -381,19 +392,20 @@ class Worker:
                     args[i] = arg_obj.requires_grad_()
 
             # TODO : use process manager to acquire rank info later
-            is_last_stage = len(self.consumer_stage_ids) == 0
+            is_last_stage = (self.pp_rank == self.actual_stage_num - 1)
 
+            # last stage doesn't need to do checkpoint, for it will do backward instantly
             if self.checkpoint and not is_last_stage:
                 with torch.no_grad():
-                    consume_result = self.cur_rank_module(*args, **kwargs)
+                    consume_result = self.module_partition(*args, **kwargs)
                 stage_outputs = None
                 stage_inputs = args
                 self.microbatch_id_to_backward_cache[microbatch_id] = BackwardCache(stage_inputs,
                                                                                     stage_outputs,
                                                                                     checkpoint=True)
             else:
-                # TODO : replace with *args, **kwargs and ensure the consume_result is a tuple
-                consume_result = self.cur_rank_module(*args, **kwargs)
+                consume_result = self.module_partition(*args, **kwargs)
+
                 stage_outputs = consume_result
                 stage_inputs = args
                 self.microbatch_id_to_backward_cache[microbatch_id] = BackwardCache(stage_inputs,
@@ -415,15 +427,13 @@ class Worker:
             stage_inputs = backward_cache.stage_inputs
             grad_tensors = args
 
-            # color_debug(f'rank_{self.rank} before backward', 'consume', 'yellow')
+            use_checkpoint = backward_cache.checkpoint
 
-            if self.checkpoint:
-                stage_outputs = [self.cur_rank_module(*stage_inputs)]
+            if use_checkpoint:
+                stage_outputs = [self.module_partition(*stage_inputs)]
 
             autograd.backward(stage_outputs, grad_tensors=grad_tensors)
 
-            # color_debug(f'rank_{self.rank} after  backward', 'consume', 'yellow')
-
             # collect grad of input tensor
             consume_result = []
             for input_node in stage_inputs:
@@ -453,7 +463,7 @@ class Worker:
                 work_item = self.work_list.pop(work_item_key)
 
             color_debug(
-                f'rank {self.rank} get a key : {work_item_key} work_item args: {tensor_shape_list(work_item.args)}',
+                f'rank {self.pp_rank} get a key : {work_item_key} work_item args: {tensor_shape_list(work_item.args)}',
                 'work loop', 'green')
 
             with self.output_list_condition_lock:
@@ -464,11 +474,8 @@ class Worker:
             consume_result = self._consume_work_item_by_phase(work_item)
 
             color_debug(
-                f'rank_{self.rank} [{work_item.phase}] finish consuming, result is {tensor_shape_list(consume_result)}',
+                f'rank_{self.pp_rank} [{work_item.phase}] finish consuming, result is {tensor_shape_list(consume_result)}',
                 'work loop', 'green')
-            # if work_item.stage_id == 1 and work_item.phase == Phase.BACKWARD:
-            #     from time import sleep
-            #     sleep(5)
             work_item.output.set_result(consume_result)
 
 
@@ -479,11 +486,11 @@ class PipelineEngineBase(ABC, nn.Module):
 
     def __init__(self,
                  module_partitions,
-                 chunk,
-                 world_size,
+                 stage_num,
                  num_microbatches,
                  device: str,
                  max_outstanding=None,
+                 chunk: int = 1,
                  use_interleave: bool = False,
                  checkpoint: bool = False) -> None:
         super().__init__()
@@ -492,55 +499,86 @@ class PipelineEngineBase(ABC, nn.Module):
         self.num_microbatches = num_microbatches
         self.device = device
         self.max_outstanding = max_outstanding
-        self.world_size = world_size
+        self.stage_num = stage_num
         self.checkpoint = checkpoint
         self.use_interleave = use_interleave
 
-        self.stage_to_worker_rref: Dict[int, PyRRef] = dict()
+        self.pp_rank_to_worker_rref: Dict[int, PyRRef] = dict()
+
+        self._check_argument()
+        self._create_pp_rank_to_rpc_worker_id()
         self._init_worker()
 
+    def _check_argument(self):
+        self.virtual_stage_num = self.stage_num * self.chunk
+
+        assert self.stage_num <= torch.cuda.device_count(), "stage_num must be smaller than device count!"
+        assert self.virtual_stage_num == len(
+            self.module_partitions), "stage_num * chunk must be equal to length of model partition!"
+        if self.use_interleave:
+            assert self.num_microbatches % self.stage_num == 0, "if you use interleaving strategy, make sure 'num_microbatches' is a multiple of stage_num!"
+
+    def _get_actual_stage_num(self):
+        return self.stage_num if self.chunk == 1 else self.virtual_stage_num
+
+    def _create_pp_rank_to_rpc_worker_id(self):
+        """create a map from model partition to stage_id, which is useful when use_interleave is True.
+        e.g. If a model is splited into 4 parts, which means len(self.module_partitions) == 3. 
+        stage_num is 2, chunk is 2, then pp_rank_to_rpc_worker_id = [0, 1, 0, 1], that means first and third part
+        of partitions will be moved to device 0 and the others to device 1
+
+        """
+        stage_num = self.stage_num
+        actual_stage_num = self._get_actual_stage_num()
+        self.pp_rank_to_rpc_worker_id = [0] * actual_stage_num
+        for pp_rank in range(actual_stage_num):
+            self.pp_rank_to_rpc_worker_id[pp_rank] = pp_rank % stage_num
+
     def _init_worker(self):
-        world_size = self.world_size
+        actual_stage_num = self._get_actual_stage_num()
+
         max_outstanding = self.max_outstanding
         checkpoint = self.checkpoint
         num_microbatches = self.num_microbatches
         device = self.device
 
-        # TODO : world size is correct ?
-        for rank in range(world_size):
-            cur_rank_module = self.module_partitions[rank]
-            self.stage_to_worker_rref[rank] = rpc.remote(rank,
-                                                         Worker,
-                                                         args=(cur_rank_module, rank, world_size, num_microbatches,
-                                                               max_outstanding, device, checkpoint))
+        for pp_rank in range(actual_stage_num):
+            module_partition = self.module_partitions[pp_rank]
+            rpc_worker_id = self.pp_rank_to_rpc_worker_id[pp_rank]
+            if device[:4] == 'cuda':
+                device = f'cuda:{rpc_worker_id}'
+            self.pp_rank_to_worker_rref[pp_rank] = rpc.remote(rpc_worker_id,
+                                                              Worker,
+                                                              args=(module_partition, pp_rank, actual_stage_num,
+                                                                    num_microbatches, max_outstanding, device,
+                                                                    checkpoint))
 
         # let each worker know global worker rref (include itself)
-        for rank in range(world_size):
-            self.stage_to_worker_rref[rank].rpc_sync().sync_global_worker_rrefs(self.stage_to_worker_rref)
+        for pp_rank in range(actual_stage_num):
+            self.pp_rank_to_worker_rref[pp_rank].rpc_sync().sync_global_worker_rrefs(self.pp_rank_to_worker_rref)
 
-    @abstractmethod
-    def forward_backward(self):
-        pass
+    def remote_parameters(self) -> Dict[int, List[torch.Tensor]]:
+        parameters = {}
+        for stage_id in self.pp_rank_to_worker_rref:
+            parameters[stage_id] = []
+            worker_rref = self.pp_rank_to_worker_rref[stage_id]
+            for p in worker_rref.rpc_sync().get_parameters():
+                parameters[stage_id].append(p)
+        return parameters
 
+    def remote_grad(self) -> Dict[int, List[torch.Tensor]]:
+        grads = {}
+        for stage_id in self.pp_rank_to_worker_rref:
+            grads[stage_id] = []
+            worker_rref = self.pp_rank_to_worker_rref[stage_id]
+            for grad in worker_rref.rpc_sync().get_parameter_gradients():
+                grads[stage_id].append(grad)
+        return grads
 
-class FillDrainPipelineEngine(PipelineEngineBase):
-
-    def __init__(self,
-                 module_partitions,
-                 chunk,
-                 world_size,
-                 num_microbatches,
-                 device: str,
-                 max_outstanding=None,
-                 use_interleave: bool = False,
-                 checkpoint: bool = False) -> None:
-        super().__init__(module_partitions, chunk, world_size, num_microbatches, device, max_outstanding,
-                         use_interleave, checkpoint)
-
-    # TODO : adjust to args and kwargs
     def forward_backward(self, batch: torch.Tensor):
-        first_stage_worker = self.stage_to_worker_rref[0]
+        first_stage_worker = self.pp_rank_to_worker_rref[0]
         microbatch_size = len(batch) // self.num_microbatches
+        actual_stage_num = self._get_actual_stage_num()
 
         microbatch_iter = range(self.num_microbatches)
         if use_progress:
@@ -550,31 +588,63 @@ class FillDrainPipelineEngine(PipelineEngineBase):
             microbatch = batch[microbatch_size * microbatch_id:microbatch_size * (microbatch_id + 1)]
 
             # forward subscribe asynchronously
-            for rank in range(1, self.world_size, 1):
-                worker_rref = self.stage_to_worker_rref[rank]
+            for pp_rank in range(1, actual_stage_num, 1):
+                worker_rref = self.pp_rank_to_worker_rref[pp_rank]
                 worker_rref.rpc_async().subscribe_producer(microbatch_id)
 
             # backward subscribe asynchronously
-            for rank in range(self.world_size - 2, -1, -1):
-                worker_rref = self.stage_to_worker_rref[rank]
+            for pp_rank in range(actual_stage_num - 2, -1, -1):
+                worker_rref = self.pp_rank_to_worker_rref[pp_rank]
                 worker_rref.rpc_async().subscribe_consumer(microbatch_id)
 
             # run one microbatch
             first_stage_worker.rpc_sync().set_input(microbatch_id, microbatch)
 
+        # wait forward
+        # TODO : all the node to output
+        forward_result = None
+        last_worker_rref = self.pp_rank_to_worker_rref[actual_stage_num - 1]
+        for microbatch_id in range(self.num_microbatches):
+            key = UniqueKey(microbatch_id, Phase.FORWARD)
+            ret = last_worker_rref.rpc_sync().get_output_by_key(key)
+            if forward_result is None:
+                forward_result = [[]] * len(ret)
+            for i in range(len(forward_result)):
+                forward_result[i].append(ret[i])
 
-class OneFOneBPipelineEngine(FillDrainPipelineEngine):
+        # wait for last backward in rank0
+        key = UniqueKey(self.num_microbatches - 1, Phase.BACKWARD)
+        first_stage_worker.rpc_sync().get_output_by_key(key)
+        return forward_result
+
+
+class FillDrainPipelineEngine(PipelineEngineBase):
 
     def __init__(self,
-                 module_partitions,
-                 chunk,
-                 world_size,
-                 num_microbatches,
+                 module_partitions: List[nn.Module],
+                 stage_num: int,
+                 num_microbatches: int,
+                 device: str,
+                 chunk: int = 1,
+                 use_interleave: bool = False,
+                 checkpoint: bool = False) -> None:
+        max_outstanding = None
+        super().__init__(module_partitions, stage_num, num_microbatches, device, max_outstanding, chunk, use_interleave,
+                         checkpoint)
+
+
+class OneFOneBPipelineEngine(PipelineEngineBase):
+
+    def __init__(self,
+                 module_partitions: List[nn.Module],
+                 stage_num: int,
+                 num_microbatches: int,
                  device: str,
                  max_outstanding=None,
+                 chunk: int = 1,
                  use_interleave: bool = False,
                  checkpoint: bool = False) -> None:
         if max_outstanding is None:
-            max_outstanding = world_size
-        super().__init__(module_partitions, chunk, world_size, num_microbatches, device, max_outstanding,
-                         use_interleave, checkpoint)
+            max_outstanding = len(module_partitions)
+        super().__init__(module_partitions, stage_num, num_microbatches, device, max_outstanding, chunk, use_interleave,
+                         checkpoint)