def test_send_backward_recv_backward(self):
self._init_model_parallel()
tensor = self.create_tensor(self.rank)
next_tensor = None
if parallel_state.is_pipeline_first_stage():
next_tensor = p2p_communication.recv_backward(
tensor_shape=self.shape, dtype=self.dtype)
elif parallel_state.is_pipeline_last_stage():
p2p_communication.send_backward(input_tensor_grad=tensor,
tensor_shape=self.shape,
dtype=self.dtype)
else:
next_tensor = p2p_communication.send_backward_recv_backward(
input_tensor_grad=tensor,
recv_next=True,
tensor_shape=self.shape,
dtype=self.dtype,
)
if parallel_state.is_pipeline_last_stage():
self.assertIsNone(next_tensor)
else:
expected_next_tensor = self.create_tensor(self.rank + 1)
self.assertEqual(next_tensor, expected_next_tensor)
def recv_backward(
tensor_shapes: List[Union[None, List[int]]],
*,
dtype: Optional[torch.dtype] = None,
) -> List[Union[None, torch.Tensor]]:
output_tensor_grads = []
for tensor_shape in tensor_shapes:
if tensor_shape is None:
output_tensor_grads.append(None)
else:
output_tensor_grads.append(p2p_communication.recv_backward(tensor_shape=tensor_shape, dtype=dtype))
return output_tensor_grads
def forward_backward_pipelining_without_interleaving(
forward_step_func: FwdStepFunc,
batch: Batch,
model: Union[torch.nn.Module, List[torch.nn.Module]],
*,
forward_only: bool,
tensor_shape: Optional[Union[List[int], torch.Size]] = None,
):
"""Run non-interleaved 1F1B schedule, with communication between pipeline stages.
This pipeline parallel scheduling consists of three steps:
1. warmup
2. 1F1B a.k.a. steady state
3. cooldown if not forward_only
Args:
forward_step_func: A function which takes a minibatch and model as its arguments and
returns model's forward output and the loss function.
The loss function is supposed to take one `torch.Tensor` and
return a `torch.Tensor` of loss and a dictionary of `str` and `torch.Tensor`.
batch: A minibatch, i.e., a list of `torch.Tensor`'s.
model: A `torch.nn.Module` or a list of `torch.nn.Module`.
Keyword args:
forward_only:
tensor_shape: Shape of tensor. Required for P2P communication.
Returns:
a list of loss `torch.Tensor`s if the last stage, empty list otherwise.
"""
# timers = get_timers()
model = listify_model(model)
if len(model) != 1:
msg = f"`model` is expected be a `nn.Module`, but {type(model)}"
raise RuntimeError(msg)
model = model[0]
# Compute number of warmup microbatches.
num_microbatches = get_num_microbatches()
num_warmup_microbatches = (
parallel_state.get_pipeline_model_parallel_world_size() -
parallel_state.get_pipeline_model_parallel_rank() - 1)
num_warmup_microbatches = min(num_warmup_microbatches, num_microbatches)
num_microbatches_remaining = num_microbatches - num_warmup_microbatches
_logger.info(f"num_microbatches: {num_microbatches}, "
f"num_warmup_microbatches: {num_warmup_microbatches}, "
f"num_microbatches_remaining: {num_microbatches_remaining}")
# Input, output tensors only need to be saved when doing backward passes
input_tensors = None
output_tensors = None
if not forward_only:
input_tensors = []
output_tensors = []
losses_reduced = []
###################################################################################################################
# Run warmup forward passes.
###################################################################################################################
_logger.info("Warmup")
for i in range(num_warmup_microbatches):
_logger.debug(f"warmup iter: {i} / {num_warmup_microbatches}")
_logger.debug("receive fwd")
input_tensor = p2p_communication.recv_forward(
tensor_shape=tensor_shape)
cur_microbatch = get_kth_microbatch(batch, i)
output_tensor = forward_step(forward_step_func, cur_microbatch, model,
input_tensor, losses_reduced)
_logger.debug("send fwd")
p2p_communication.send_forward(output_tensor,
tensor_shape=tensor_shape)
if not forward_only:
input_tensors.append(input_tensor)
output_tensors.append(output_tensor)
# Before running 1F1B, need to receive first forward tensor.
# If all microbatches are run in warmup / cooldown phase, then no need to
# receive this tensor here.
if num_microbatches_remaining > 0:
_logger.debug("recv_forward before steady state start")
input_tensor = p2p_communication.recv_forward(
tensor_shape=tensor_shape)
###################################################################################################################
# Run 1F1B in steady state.
###################################################################################################################
_logger.info("Steady phase")
for i in range(num_microbatches_remaining):
_logger.debug(f"steady iter: {i} / {num_microbatches_remaining}")
last_iteration = i == (num_microbatches_remaining - 1)
cur_microbatch = get_kth_microbatch(batch, i + num_warmup_microbatches)
output_tensor = forward_step(forward_step_func, cur_microbatch, model,
input_tensor, losses_reduced)
if forward_only:
_logger.debug("send fwd")
p2p_communication.send_forward(output_tensor,
tensor_shape=tensor_shape)
if not last_iteration:
_logger.debug("receive fwd (last iteration)")
input_tensor = p2p_communication.recv_forward(
tensor_shape=tensor_shape)
else:
_logger.debug("send fwd & receive bwd")
output_tensor_grad = p2p_communication.send_forward_recv_backward(
output_tensor, tensor_shape=tensor_shape)
# Add input_tensor and output_tensor to end of list.
input_tensors.append(input_tensor)
output_tensors.append(output_tensor)
# Pop input_tensor and output_tensor from the start of the list for the backward pass.
input_tensor = input_tensors.pop(0)
output_tensor = output_tensors.pop(0)
input_tensor_grad = backward_step(input_tensor, output_tensor,
output_tensor_grad)
if last_iteration:
input_tensor = None
_logger.debug("send bwd")
p2p_communication.send_backward(input_tensor_grad,
tensor_shape=tensor_shape)
else:
_logger.debug("send bwd and receive fwd")
input_tensor = p2p_communication.send_backward_recv_forward(
input_tensor_grad, tensor_shape=tensor_shape)
###################################################################################################################
# Run cooldown backward passes.
###################################################################################################################
_logger.info("Cooldown phase")
if not forward_only:
for i in range(num_warmup_microbatches):
_logger.debug(f"cooldown iter: {i} / {num_warmup_microbatches}")
input_tensor = input_tensors.pop(0)
output_tensor = output_tensors.pop(0)
_logger.debug("receive bwd")
output_tensor_grad = p2p_communication.recv_backward(
tensor_shape=tensor_shape)
input_tensor_grad = backward_step(input_tensor, output_tensor,
output_tensor_grad)
_logger.debug("send bwd")
p2p_communication.send_backward(input_tensor_grad,
tensor_shape=tensor_shape)
return losses_reduced
def _forward_backward_pipelining_with_interleaving(
forward_step_func: FwdStepFunc,
batch: List[Optional[Batch]],
model: List[torch.nn.Module],
*,
forward_only: bool,
tensor_shape: Optional[Union[List[int], torch.Size]] = None,
dtype: Optional[torch.dtype] = None,
grad_scaler: Optional[torch.cuda.amp.GradScaler] = None,
disable_autocast: bool = False,
deallocate_pipeline_outputs: bool = False,
**kwargs,
) -> List[Union[torch.Tensor, Sequence[torch.Tensor]]]:
"""Run interleaved 1F1B schedule with communication between pipeline stages as needed.
This function assumes `batch` and `model` is a list of `Batch`'s and a list of `torch.nn.Module`, respectively.
This means that model is split into model chunks.
This pipeline parallel scheduling consists of three steps:
1. warmup
2. 1F1B a.k.a. steady state
3. cooldown
Note that if `forward_only` this scheduling consists of only warmup phase.
Args:
forward_step_func: A function which takes a minibatch and model as its arguments and
returns model's forward output and the loss function.
The loss function is supposed to take one `torch.Tensor` and
return a `torch.Tensor` of loss and a dictionary of `str` and `torch.Tensor`.
batch: A minibatch, i.e., a list of `torch.Tensor`'s.
model: A `torch.nn.Module` or a list of `torch.nn.Module`.
Keyword args:
forward_only:
tensor_shape: Shape of tensor.
dtype: dtype used in p2p communication. If ``None`` (default value),
torch.float32 will be used even if ``autocast`` is enabled.
grad_scaler:
disable_autocast:
deallocate_pipeline_outputs: If :obj:`True`, free the data of the output tensor of
each pipeline stage. Experimental.
Returns:
a list of loss `torch.Tensor`s if the last stage, empty list otherwise.
"""
if not isinstance(model, list):
raise RuntimeError("`model` must be a list of `nn.Module`'s'")
num_model_chunks: int = len(model)
input_tensors: List[List[Union[None, torch.Tensor]]] = [
[] for _ in range(num_model_chunks)
]
output_tensors: List[List[Union[None, torch.Tensor]]] = [
[] for _ in range(num_model_chunks)
]
curr_iters: List[int] = [0 for _ in range(num_model_chunks)]
losses_reduced: List[Union[None, torch.Tensor]] = []
if not forward_only:
output_tensor_grads: List[List[Union[None, torch.Tensor]]] = [
[] for _ in range(num_model_chunks)
]
pipeline_parallel_size: int = parallel_state.get_pipeline_model_parallel_world_size(
)
pipeline_parallel_rank: int = parallel_state.get_pipeline_model_parallel_rank(
)
# Compute number of warmup and remaining microbatches.
num_microbatches: int = get_num_microbatches() * num_model_chunks
all_warmup_microbatches: bool = False
if forward_only:
num_warmup_microbatches: int = num_microbatches
else:
# Run all forward passes and then all backward passes if number of
# microbatches is just the number of pipeline stages.
# Otherwise, perform (num_model_chunks-1)*pipeline_parallel_size on
# all workers, followed by more microbatches after depending on
# stage ID (more forward passes for earlier stages, later stages can
# immediately start with 1F1B).
if get_num_microbatches() == pipeline_parallel_size:
num_warmup_microbatches = num_microbatches
all_warmup_microbatches = True
else:
num_warmup_microbatches = (pipeline_parallel_size -
pipeline_parallel_rank - 1) * 2
num_warmup_microbatches += (num_model_chunks -
1) * pipeline_parallel_size
num_warmup_microbatches = min(num_warmup_microbatches,
num_microbatches)
num_microbatches_remaining: int = num_microbatches - num_warmup_microbatches
_logger.info(f"num_microbatches: {num_microbatches}, "
f"num_warmup_microbatches: {num_warmup_microbatches}, "
f"num_microbatches_remaining: {num_microbatches_remaining}")
###################################################################################################################
# Helper function definitions.
###################################################################################################################
def get_model_chunk_id(microbatch_id: int, forward: bool) -> int:
"""Helper function to get the model chunk ID given the iteration number."""
pipeline_parallel_size = parallel_state.get_pipeline_model_parallel_world_size(
)
microbatch_id_in_group = microbatch_id % (pipeline_parallel_size *
num_model_chunks)
model_chunk_id = microbatch_id_in_group // pipeline_parallel_size
if not forward:
model_chunk_id = num_model_chunks - model_chunk_id - 1
return model_chunk_id
def forward_step_helper(microbatch_id: int,
curr_iters: List[int]) -> torch.Tensor:
"""Helper method to run forward step with model split into chunks
(run set_virtual_pipeline_model_parallel_rank() before calling forward_step()).
"""
model_chunk_id = get_model_chunk_id(microbatch_id, forward=True)
parallel_state.set_virtual_pipeline_model_parallel_rank(model_chunk_id)
# forward step
if (parallel_state.is_pipeline_first_stage()
and len(input_tensors[model_chunk_id]) == len(
output_tensors[model_chunk_id])):
input_tensors[model_chunk_id].append(None)
input_tensor = input_tensors[model_chunk_id][-1]
output_tensor = forward_step(
forward_step_func,
get_kth_microbatch(batch, curr_iters[model_chunk_id]),
model[model_chunk_id],
input_tensor,
losses_reduced,
dtype,
disable_autocast,
)
curr_iters[model_chunk_id] += 1
output_tensors[model_chunk_id].append(output_tensor)
# if forward-only, no need to save tensors for a backward pass
if forward_only:
input_tensors[model_chunk_id].pop()
output_tensors[model_chunk_id].pop()
return output_tensor
def backward_step_helper(microbatch_id: int) -> torch.Tensor:
"""Helper method to run backward step with model split into chunks
(run set_virtual_pipeline_model_parallel_rank() before calling backward_step()).
"""
model_chunk_id = get_model_chunk_id(microbatch_id, forward=False)
model_type = get_model_type(model[model_chunk_id])
parallel_state.set_virtual_pipeline_model_parallel_rank(model_chunk_id)
if parallel_state.is_pipeline_last_stage():
if len(output_tensor_grads[model_chunk_id]) == 0:
output_tensor_grads[model_chunk_id].append(None)
input_tensor = input_tensors[model_chunk_id].pop(0)
output_tensor = output_tensors[model_chunk_id].pop(0)
output_tensor_grad = output_tensor_grads[model_chunk_id].pop(0)
input_tensor_grad = backward_step(
input_tensor,
output_tensor,
output_tensor_grad,
model_type=model_type,
grad_scaler=grad_scaler,
deallocate_pipeline_outputs=deallocate_pipeline_outputs)
return input_tensor_grad
###################################################################################################################
# Run warmup forward passes.
###################################################################################################################
parallel_state.set_virtual_pipeline_model_parallel_rank(0)
input_tensors[0].append(
p2p_communication.recv_forward(tensor_shape=tensor_shape, dtype=dtype))
_logger.info("Warmup phase")
for k in range(num_warmup_microbatches):
_logger.debug(f"warmup iter: {k} / {num_warmup_microbatches}")
output_tensor = forward_step_helper(k, curr_iters)
# Determine if tensor should be received from previous stage.
next_forward_model_chunk_id = get_model_chunk_id(k + 1, forward=True)
recv_prev = True
if parallel_state.is_pipeline_first_stage(ignore_virtual=True):
if next_forward_model_chunk_id == 0:
recv_prev = False
if k == (num_microbatches - 1):
recv_prev = False
_logger.debug(
f"next fwd model chunk ID: {next_forward_model_chunk_id}, recv_prev: {recv_prev}"
)
# Don't send tensor downstream if on last stage.
if parallel_state.is_pipeline_last_stage():
_logger.debug("Pipeline last stage, not sending tensor downstream")
output_tensor = None
# Send and receive tensors as appropriate (send tensors computed
# in this iteration; receive tensors for next iteration).
if k == (num_warmup_microbatches -
1) and not forward_only and not all_warmup_microbatches:
input_tensor_grad = None
recv_next = True
if parallel_state.is_pipeline_last_stage(ignore_virtual=True):
recv_next = False
_logger.debug("send fwd&bwd and receive fwd&bwd")
(
input_tensor,
output_tensor_grad,
) = p2p_communication.send_forward_backward_recv_forward_backward(
output_tensor,
input_tensor_grad,
recv_prev=recv_prev,
recv_next=recv_next,
tensor_shape=tensor_shape,
dtype=dtype,
)
output_tensor_grads[num_model_chunks -
1].append(output_tensor_grad)
else:
_logger.debug("send fwd and receive fwd")
input_tensor = p2p_communication.send_forward_recv_forward(
output_tensor,
recv_prev=recv_prev,
tensor_shape=tensor_shape,
dtype=dtype)
free_output_tensor(output_tensor, deallocate_pipeline_outputs)
input_tensors[next_forward_model_chunk_id].append(input_tensor)
###################################################################################################################
# Run 1F1B in steady state.
###################################################################################################################
_logger.info("Steady phase")
for k in range(num_microbatches_remaining):
# Forward pass.
_logger.debug(f" steady phase iter {k} / {num_microbatches_remaining}")
forward_k = k + num_warmup_microbatches
output_tensor = forward_step_helper(forward_k, curr_iters)
# Backward pass.
backward_k = k
input_tensor_grad = backward_step_helper(backward_k)
# Send output_tensor and input_tensor_grad, receive input_tensor
# and output_tensor_grad.
# Determine if current stage has anything to send in either direction,
# otherwise set tensor to None.
forward_model_chunk_id = get_model_chunk_id(forward_k, forward=True)
parallel_state.set_virtual_pipeline_model_parallel_rank(
forward_model_chunk_id)
if parallel_state.is_pipeline_last_stage():
output_tensor = None
backward_model_chunk_id = get_model_chunk_id(backward_k, forward=False)
parallel_state.set_virtual_pipeline_model_parallel_rank(
backward_model_chunk_id)
_logger.debug(
f"fwd/bwd model chunk id: {forward_model_chunk_id}/{backward_model_chunk_id}"
)
if parallel_state.is_pipeline_first_stage():
input_tensor_grad = None
# Determine if peers are sending, and where in data structure to put
# received tensors.
recv_prev = True
if parallel_state.is_pipeline_first_stage(ignore_virtual=True):
# First stage is ahead of last stage by (pipeline_parallel_size - 1).
next_forward_model_chunk_id = get_model_chunk_id(
forward_k - (pipeline_parallel_size - 1), forward=True)
if next_forward_model_chunk_id == (num_model_chunks - 1):
recv_prev = False
next_forward_model_chunk_id += 1
else:
next_forward_model_chunk_id = get_model_chunk_id(forward_k + 1,
forward=True)
recv_next = True
if parallel_state.is_pipeline_last_stage(ignore_virtual=True):
# Last stage is ahead of first stage by (pipeline_parallel_size - 1).
next_backward_model_chunk_id = get_model_chunk_id(
backward_k - (pipeline_parallel_size - 1), forward=False)
if next_backward_model_chunk_id == 0:
recv_next = False
next_backward_model_chunk_id -= 1
else:
next_backward_model_chunk_id = get_model_chunk_id(backward_k + 1,
forward=False)
# If last iteration, don't receive; we already received one extra
# before the start of the for loop.
if k == (num_microbatches_remaining - 1):
recv_prev = False
# Communicate tensors.
_logger.debug("send fwd&bwd and receive fwd&bwd")
(
input_tensor,
output_tensor_grad,
) = p2p_communication.send_forward_backward_recv_forward_backward(
output_tensor,
input_tensor_grad,
recv_prev=recv_prev,
recv_next=recv_next,
tensor_shape=tensor_shape,
dtype=dtype,
)
free_output_tensor(output_tensor, deallocate_pipeline_outputs)
# Put input_tensor and output_tensor_grad in data structures in the
# right location.
if recv_prev:
input_tensors[next_forward_model_chunk_id].append(input_tensor)
if recv_next:
output_tensor_grads[next_backward_model_chunk_id].append(
output_tensor_grad)
###################################################################################################################
# Run cooldown backward passes (flush out pipeline).
###################################################################################################################
_logger.info("Cooldown phase")
if not forward_only:
if all_warmup_microbatches:
output_tensor_grads[num_model_chunks - 1].append(
p2p_communication.recv_backward(tensor_shape=tensor_shape,
dtype=dtype))
for k in range(num_microbatches_remaining, num_microbatches):
_logger.debug(
f"cooldown iter {k} in range({num_microbatches_remaining}, {num_microbatches})"
)
input_tensor_grad = backward_step_helper(k)
next_backward_model_chunk_id = get_model_chunk_id(k + 1,
forward=False)
recv_next = True
if parallel_state.is_pipeline_last_stage(ignore_virtual=True):
if next_backward_model_chunk_id == (num_model_chunks - 1):
recv_next = False
if k == (num_microbatches - 1):
recv_next = False
output_tensor_grads[next_backward_model_chunk_id].append(
p2p_communication.send_backward_recv_backward(
input_tensor_grad,
recv_next=recv_next,
tensor_shape=tensor_shape,
dtype=dtype))
return losses_reduced