def recv_backward(tensor_shapes, timers):
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, timers=timers))
return output_tensor_grads
def forward_backward_pipelining_with_interleaving(forward_step_func,
data_iterator, model,
optimizer, timers,
forward_only):
"""Run interleaved 1F1B schedule (model split into model chunks), with
communication between pipeline stages as needed.
Returns dictionary with losses if the last stage, empty dict otherwise."""
input_tensors = [[] for _ in range(len(model))]
output_tensors = [[] for _ in range(len(model))]
losses_reduced = []
if not forward_only:
output_tensor_grads = [[] for _ in range(len(model))]
pipeline_parallel_size = mpu.get_pipeline_model_parallel_world_size()
pipeline_parallel_rank = mpu.get_pipeline_model_parallel_rank()
args = get_args()
tensor_shape = (args.seq_length, args.micro_batch_size, args.hidden_size)
# Compute number of warmup and remaining microbatches.
num_model_chunks = len(model)
num_microbatches = get_num_microbatches() * num_model_chunks
all_warmup_microbatches = False
if forward_only:
num_warmup_microbatches = 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 = \
num_microbatches - num_warmup_microbatches
def get_model_chunk_id(microbatch_id, forward):
"""Helper method to get the model chunk ID given the iteration number."""
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):
"""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)
mpu.set_virtual_pipeline_model_parallel_rank(model_chunk_id)
# forward step
if mpu.is_pipeline_first_stage():
if 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,
data_iterator[model_chunk_id],
model[model_chunk_id], input_tensor,
losses_reduced)
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):
"""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)
mpu.set_virtual_pipeline_model_parallel_rank(model_chunk_id)
if mpu.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(optimizer,
input_tensor,
output_tensor,
output_tensor_grad)
return input_tensor_grad
# Run warmup forward passes.
mpu.set_virtual_pipeline_model_parallel_rank(0)
input_tensors[0].append(
p2p_communication.recv_forward(tensor_shape, timers=timers))
for k in range(num_warmup_microbatches):
output_tensor = forward_step_helper(k)
# 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 mpu.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
# Don't send tensor downstream if on last stage.
if mpu.is_pipeline_last_stage():
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 mpu.is_pipeline_last_stage(ignore_virtual=True):
recv_next = False
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,
timers=timers)
output_tensor_grads[num_model_chunks -
1].append(output_tensor_grad)
else:
input_tensor = \
p2p_communication.send_forward_recv_forward(
output_tensor, recv_prev=recv_prev,
tensor_shape=tensor_shape,
timers=timers)
input_tensors[next_forward_model_chunk_id].append(input_tensor)
deallocate_output_tensor(output_tensor)
# Run 1F1B in steady state.
for k in range(num_microbatches_remaining):
# Forward pass.
forward_k = k + num_warmup_microbatches
output_tensor = forward_step_helper(forward_k)
# 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)
mpu.set_virtual_pipeline_model_parallel_rank(forward_model_chunk_id)
if mpu.is_pipeline_last_stage():
output_tensor = None
backward_model_chunk_id = get_model_chunk_id(backward_k, forward=False)
mpu.set_virtual_pipeline_model_parallel_rank(backward_model_chunk_id)
if mpu.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 mpu.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 mpu.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.
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, timers=timers)
deallocate_output_tensor(output_tensor)
# 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).
if not forward_only:
if all_warmup_microbatches:
output_tensor_grads[num_model_chunks - 1].append(
p2p_communication.recv_backward(tensor_shape, timers=timers))
for 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 mpu.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,
timers=timers))
return losses_reduced
def forward_backward_pipelining_without_interleaving(forward_step_func,
data_iterator, model,
optimizer, timers,
forward_only):
"""Run non-interleaved 1F1B schedule, with communication between pipeline
stages.
Returns dictionary with losses if the last stage, empty dict otherwise."""
timers = get_timers()
assert len(model) == 1
model = model[0]
# Compute number of warmup microbatches.
num_microbatches = get_num_microbatches()
num_warmup_microbatches = \
(mpu.get_pipeline_model_parallel_world_size() -
mpu.get_pipeline_model_parallel_rank() - 1)
num_warmup_microbatches = min(num_warmup_microbatches, num_microbatches)
num_microbatches_remaining = \
num_microbatches - num_warmup_microbatches
input_tensors = []
output_tensors = []
losses_reduced = []
# Run warmup forward passes.
for i in range(num_warmup_microbatches):
input_tensor = p2p_communication.recv_forward(timers)
output_tensor = forward_step(forward_step_func, data_iterator, model,
input_tensor, losses_reduced)
p2p_communication.send_forward(output_tensor, timers)
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:
input_tensor = p2p_communication.recv_forward(timers)
# Run 1F1B in steady state.
for i in range(num_microbatches_remaining):
last_iteration = (i == (num_microbatches_remaining - 1))
output_tensor = forward_step(forward_step_func, data_iterator, model,
input_tensor, losses_reduced)
if forward_only:
p2p_communication.send_forward(output_tensor, timers)
else:
output_tensor_grad = \
p2p_communication.send_forward_recv_backward(output_tensor,
timers)
# Add input_tensor and output_tensor to end of list, then pop from the
# start of the list for backward pass.
input_tensors.append(input_tensor)
output_tensors.append(output_tensor)
if forward_only:
if not last_iteration:
input_tensor = p2p_communication.recv_forward(timers)
else:
input_tensor, output_tensor = input_tensors.pop(
0), output_tensors.pop(0)
input_tensor_grad = \
backward_step(optimizer, input_tensor, output_tensor,
output_tensor_grad)
if last_iteration:
input_tensor = None
p2p_communication.send_backward(input_tensor_grad, timers)
else:
input_tensor = \
p2p_communication.send_backward_recv_forward(
input_tensor_grad, timers)
# Run cooldown backward passes.
if not forward_only:
for i in range(num_warmup_microbatches):
input_tensor = input_tensors.pop(0)
output_tensor = output_tensors.pop(0)
output_tensor_grad = p2p_communication.recv_backward(timers)
input_tensor_grad = \
backward_step(optimizer, input_tensor, output_tensor,
output_tensor_grad)
p2p_communication.send_backward(input_tensor_grad, timers)
return losses_reduced