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lightning/pytorch_lightning/trainer/training_loop.py

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# Copyright The PyTorch Lightning team.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
The lightning training loop handles everything except the actual computations of your model.
To decide what will happen in your training loop, define the `training_step` function.
Below are all the things lightning automates for you in the training loop.
Accumulated gradients
---------------------
Accumulated gradients runs K small batches of size N before doing a backwards pass.
The effect is a large effective batch size of size KxN.
.. code-block:: python
# DEFAULT (ie: no accumulated grads)
trainer = Trainer(accumulate_grad_batches=1)
Force training for min or max epochs
------------------------------------
It can be useful to force training for a minimum number of epochs or limit to a max number
.. code-block:: python
# DEFAULT
trainer = Trainer(min_epochs=1, max_epochs=1000)
Force disable early stop
------------------------
To disable early stopping pass None to the early_stop_callback
.. code-block:: python
# DEFAULT
trainer = Trainer(early_stop_callback=None)
Gradient Clipping
-----------------
Gradient clipping may be enabled to avoid exploding gradients.
Specifically, this will `clip the gradient norm computed over all model parameters
`together <https://pytorch.org/docs/stable/nn.html#torch.nn.utils.clip_grad_norm_>`_.
.. code-block:: python
# DEFAULT (ie: don't clip)
trainer = Trainer(gradient_clip_val=0)
# clip gradients with norm above 0.5
trainer = Trainer(gradient_clip_val=0.5)
Inspect gradient norms
----------------------
Looking at grad norms can help you figure out where training might be going wrong.
.. code-block:: python
# DEFAULT (-1 doesn't track norms)
trainer = Trainer(track_grad_norm=-1)
# track the LP norm (P=2 here)
trainer = Trainer(track_grad_norm=2)
Set how much of the training set to check
-----------------------------------------
If you don't want to check 100% of the training set (for debugging or if it's huge), set this flag.
limit_train_batches will be overwritten by overfit_batches if `overfit_batches > 0`
.. code-block:: python
# DEFAULT
trainer = Trainer(limit_train_batches=1.0)
# check 10% only
trainer = Trainer(limit_train_batches=0.1)
# check 10 batches only
trainer = Trainer(limit_train_batches=10)
Packed sequences as inputs
--------------------------
When using PackedSequence, do 2 things:
1. return either a padded tensor in dataset or a list of variable length tensors
in the dataloader collate_fn (example above shows the list implementation).
2. Pack the sequence in forward or training and validation steps depending on use case.
.. code-block:: python
# For use in dataloader
def collate_fn(batch):
x = [item[0] for item in batch]
y = [item[1] for item in batch]
return x, y
# In module
def training_step(self, batch, batch_idx):
x = rnn.pack_sequence(batch[0], enforce_sorted=False)
y = rnn.pack_sequence(batch[1], enforce_sorted=False)
Truncated Backpropagation Through Time
--------------------------------------
There are times when multiple backwards passes are needed for each batch.
For example, it may save memory to use Truncated Backpropagation Through Time when training RNNs.
When this flag is enabled each batch is split into sequences of size truncated_bptt_steps
and passed to training_step(...) separately. A default splitting function is provided,
however, you can override it for more flexibility. See `tbptt_split_batch`.
.. code-block:: python
# DEFAULT (single backwards pass per batch)
trainer = Trainer(truncated_bptt_steps=None)
# (split batch into sequences of size 2)
trainer = Trainer(truncated_bptt_steps=2)
NaN detection and intervention
------------------------------
When the `terminate_on_nan` flag is enabled, after every forward pass during training, Lightning will
check that
1. the loss you return in `training_step` is finite (not NaN and not +/-inf)
2. the model parameters have finite values.
Lightning will terminate the training loop with an error message if NaN or infinite
values are detected. If this happens, you should investigate numerically unstable operations
in your model.
.. code-block:: python
# DEFAULT (won't perform the NaN check)
trainer = Trainer(terminate_on_nan=False)
# (NaN check each batch and terminate on NaN or infinite values)
trainer = Trainer(terminate_on_nan=True)
"""
import os
import subprocess
from abc import ABC, abstractmethod
from typing import Callable
from typing import Union, List
import numpy as np
import torch
from torch.utils.data import DataLoader
import torch.distributed as torch_distrib
from copy import copy
from pytorch_lightning import _logger as log
from pytorch_lightning.callbacks.base import Callback
from pytorch_lightning.callbacks import ModelCheckpoint
from pytorch_lightning.core.lightning import LightningModule
from pytorch_lightning.loggers import LightningLoggerBase
from pytorch_lightning.trainer.supporters import TensorRunningAccum, Accumulator
from pytorch_lightning.utilities import rank_zero_warn, NATIVE_AMP_AVALAIBLE
from pytorch_lightning.utilities.exceptions import MisconfigurationException
from pytorch_lightning.utilities.parsing import AttributeDict
from pytorch_lightning.utilities.memory import recursive_detach
from pytorch_lightning.core.step_result import EvalResult, TrainResult, Result
try:
from apex import amp
except ImportError:
APEX_AVAILABLE = False
else:
APEX_AVAILABLE = True
try:
import torch_xla.distributed.parallel_loader as xla_pl
import torch_xla.core.xla_model as xm
except ImportError:
XLA_AVAILABLE = False
else:
XLA_AVAILABLE = True
try:
import horovod.torch as hvd
except (ModuleNotFoundError, ImportError):
HOROVOD_AVAILABLE = False
else:
HOROVOD_AVAILABLE = True
# constant which signals should be catched for graceful trainer shutdown
SIGNAL_TERMINATE = ('SIGTERM', 'SIGSEGV', 'SIGINT')
class TrainerTrainLoopMixin(ABC):
# this is just a summary on variables used in this abstract class,
# the proper values/initialisation should be done in child class
max_epochs: int
min_epochs: int
on_gpu: bool
use_ddp: bool
use_dp: bool
use_ddp2: bool
use_horovod: bool
use_single_gpu: bool
use_tpu: bool
data_parallel_device_ids: ...
check_val_every_n_epoch: ...
num_training_batches: int
val_check_batch: ...
disable_validation: bool
fast_dev_run: ...
accumulation_scheduler: ...
lr_schedulers: ...
early_stop_callback: ...
callback_metrics: ...
logger: Union[LightningLoggerBase, bool]
global_step: int
testing: bool
log_save_interval: float
global_rank: int
row_log_interval: float
truncated_bptt_steps: ...
optimizers: ...
optimizer_frequencies: ...
accumulate_grad_batches: int
track_grad_norm: ...
model: LightningModule
interrupted: bool
running_loss: ...
progress_bar_dict: ...
reduce_lr_on_plateau_scheduler: ...
profiler: ...
batch_idx: int
precision: ...
train_dataloader: DataLoader
reload_dataloaders_every_epoch: bool
max_steps: int
min_steps: int
total_batch_idx: int
terminate_on_nan: bool
tpu_id: int
interactive_ddp_procs: ...
# Callback system
callbacks: List[Callback]
on_train_start: Callable
on_train_end: Callable
on_batch_start: Callable
on_batch_end: Callable
on_epoch_start: Callable
on_epoch_end: Callable
on_validation_end: Callable
on_keyboard_interrupt: Callable
on_train_epoch_start: Callable
on_train_epoch_end: Callable
@abstractmethod
def get_model(self) -> LightningModule:
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def is_function_implemented(self, *args, **kwargs):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def run_evaluation(self, *args, **kwargs):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def transfer_batch_to_gpu(self, *args):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def transfer_batch_to_tpu(self, *args):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def clip_gradients(self):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def detect_nan_tensors(self, *args):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def is_overridden(self, *args):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def add_progress_bar_metrics(self, *args):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def log_metrics(self, *args):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def process_output(self, *args):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def reset_train_dataloader(self, *args):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def reset_val_dataloader(self, model):
"""Warning: this is just empty shell for code implemented in other class."""
@abstractmethod
def has_arg(self, *args):
"""Warning: this is just empty shell for code implemented in other class."""
def train(self):
# add signal handlers for process kills
# def _signal_kill_handler(*args):
# return TrainerTrainLoopMixin.run_training_teardown(self)
#
# orig_signal_handlers = {}
# for sig_name in SIGNAL_TERMINATE:
# orig_signal_handlers[sig_name] = signal.signal(getattr(signal, sig_name),
# _signal_kill_handler)
# get model
model = self.get_model()
# enable train mode
model.train()
# enable gradients
torch.set_grad_enabled(True)
# load data
# if reload_dataloaders_every_epoch, this is moved to the epoch loop
if not self.reload_dataloaders_every_epoch:
self.reset_train_dataloader(model)
if model.val_dataloader is not None:
self.reset_val_dataloader(model)
# Train start events
with self.profiler.profile('on_train_start'):
# callbacks
self.on_train_start()
# model hooks
model.on_train_start()
try:
# run all epochs
for epoch in range(self.current_epoch, self.max_epochs):
# reset train dataloader
if self.reload_dataloaders_every_epoch:
self.reset_train_dataloader(model)
# set seed for distributed sampler (enables shuffling for each epoch)
if (self.use_ddp or self.use_horovod) \
and hasattr(self.train_dataloader, 'sampler') \
and hasattr(self.train_dataloader.sampler, 'set_epoch'):
self.train_dataloader.sampler.set_epoch(epoch)
# update training progress in trainer and model
model.current_epoch = epoch
self.current_epoch = epoch
# changing gradient according accumulation_scheduler
self.accumulation_scheduler.on_epoch_start(self, self.get_model())
# stores accumulated grad fractions per batch
self.batch_loss_value = TensorRunningAccum(
window_length=self.accumulate_grad_batches
)
# -----------------
# RUN TNG EPOCH
# -----------------
self.run_training_epoch()
if self.max_steps and self.max_steps <= self.global_step:
self.run_training_teardown()
return
# update LR schedulers
self.update_learning_rates(interval='epoch')
# early stopping
met_min_epochs = epoch >= self.min_epochs - 1
met_min_steps = self.global_step >= self.min_steps if self.min_steps else True
if self.should_stop:
if (met_min_epochs and met_min_steps):
self.run_training_teardown()
return
else:
log.info('Trainer was signaled to stop but required minimum epochs'
f' ({self.min_epochs}) or minimum steps ({self.min_steps}) has'
' not been met. Training will continue...')
self.run_training_teardown()
except KeyboardInterrupt:
rank_zero_warn('Detected KeyboardInterrupt, attempting graceful shutdown...')
# user could press ctrl+c many times... only shutdown once
if not self.interrupted:
self.interrupted = True
self.on_keyboard_interrupt()
self.run_training_teardown()
def prepare_train_loop_dataloader(self, train_dataloader):
# on TPU we have to wrap it under the ParallelLoader
if self.use_tpu:
device = xm.xla_device(self.tpu_id)
train_dataloader = xla_pl.ParallelLoader(train_dataloader, [device])
train_dataloader = train_dataloader.per_device_loader(device)
return train_dataloader
def run_on_epoch_start_hook(self, model):
# Epoch start events
with self.profiler.profile('on_epoch_start'):
# callbacks
self.on_epoch_start()
# model hooks
if self.is_function_implemented('on_epoch_start'):
model.on_epoch_start()
# Epoch start events
with self.profiler.profile('on_train_epoch_start'):
# callbacks
self.on_train_epoch_start()
# model hooks
if self.is_function_implemented('on_train_epoch_start'):
model.on_train_epoch_start()
def run_training_epoch(self):
# get model
model = self.get_model()
# Epoch start events
self.run_on_epoch_start_hook(model)
# modify dataloader if needed (ddp, etc...)
train_dataloader = self.prepare_train_loop_dataloader(self.train_dataloader)
# bookkeeping
epoch_output = []
should_check_val = False
# structured result accumulators for callbacks
early_stopping_accumulator = Accumulator()
checkpoint_accumulator = Accumulator()
# run epoch
for batch_idx, (batch, is_last_batch) in self.profiler.profile_iterable(
enumerate(_with_is_last(train_dataloader)), "get_train_batch"
):
# stop epoch if we limited the number of training batches
if batch_idx >= self.num_training_batches:
break
self.batch_idx = batch_idx
model.global_step = self.global_step
# ------------------------------------
# TRAINING_STEP + TRAINING_STEP_END
# ------------------------------------
batch_output = self.run_training_batch(batch, batch_idx)
# only track outputs when user implements training_epoch_end
# otherwise we will build up unnecessary memory
step_out = batch_output.training_step_output_for_epoch_end
should_auto_reduce_train_result = isinstance(step_out, Result) and step_out.should_reduce_on_epoch_end
if isinstance(step_out, dict) and 'early_stop_on' in step_out:
early_stopping_accumulator.accumulate(step_out['early_stop_on'])
if isinstance(step_out, dict) and 'checkpoint_on' in step_out:
checkpoint_accumulator.accumulate(step_out['checkpoint_on'])
if self.is_overridden('training_epoch_end', model=self.get_model()) or should_auto_reduce_train_result:
epoch_output.append(batch_output.training_step_output_for_epoch_end)
# update LR schedulers
self.update_train_loop_lr_schedulers()
# when returning -1 from train_step, we end epoch early
self.should_stop = batch_output.signal == -1
# -----------------------------------------
# VALIDATE IF NEEDED + CHECKPOINT CALLBACK
# -----------------------------------------
should_check_val = self.should_check_val(batch_idx, is_last_batch)
if should_check_val:
self.run_evaluation(test_mode=False)
# -----------------------------------------
# SAVE LOGGERS (ie: Tensorboard, etc...)
# -----------------------------------------
self.save_loggers_in_training_loop(batch_idx)
# -----------------------------------------
# SAVE METRICS TO LOGGERS
# -----------------------------------------
self.save_train_loop_metrics_to_loggers(batch_idx, batch_output)
# progress global step according to grads progress
self.increment_accumulated_grad_global_step()
# max steps reached, end training
if self.max_steps is not None and self.max_steps == self.global_step:
break
# end epoch early
# stop when the flag is changed or we've gone past the amount
# requested in the batches
if self.should_stop:
break
# let ddp devices catch up when using horovod
self.sync_horovod()
# process epoch outputs
self.run_training_epoch_end(epoch_output, checkpoint_accumulator, early_stopping_accumulator)
# checkpoint callback
self.check_checkpoint_callback(should_check_val)
# epoch end hook
self.run_on_epoch_end_hook(model)
def check_checkpoint_callback(self, should_check_val):
# when no val loop is present or fast-dev-run still need to call checkpoints
# TODO bake this logic into the checkpoint callback
should_activate = not self.is_overridden('validation_step') and not should_check_val
if should_activate:
checkpoint_callbacks = [c for c in self.callbacks if isinstance(c, ModelCheckpoint)]
[c.on_validation_end(self, self.get_model()) for c in checkpoint_callbacks]
def update_train_loop_lr_schedulers(self):
if (self.batch_idx + 1) % self.accumulate_grad_batches == 0:
# update lr
self.update_learning_rates(interval='step')
def run_on_epoch_end_hook(self, model):
with self.profiler.profile('on_epoch_end'):
# callbacks
self.on_epoch_end()
# model hooks
if self.is_function_implemented('on_epoch_end'):
model.on_epoch_end()
with self.profiler.profile('on_train_epoch_end'):
# callbacks
self.on_train_epoch_end()
# model hooks
if self.is_function_implemented('on_train_epoch_end'):
model.on_train_epoch_end()
def run_training_epoch_end(self, epoch_output, checkpoint_accumulator, early_stopping_accumulator):
model = self.get_model()
is_result_obj = len(epoch_output) > 0 and isinstance(epoch_output[0], Result)
epoch_log_metrics = {}
epoch_callback_metrics = {}
epoch_progress_bar_metrics = {}
# -----------------------
# Calculate epoch callback values if given
# -----------------------
if checkpoint_accumulator.num_values > 0:
epoch_callback_metrics['checkpoint_on'] = checkpoint_accumulator.mean()
if early_stopping_accumulator.num_values > 0:
epoch_callback_metrics['early_stop_on'] = early_stopping_accumulator.mean()
# --------------------------
# EPOCH END STEP IF DEFINED
# --------------------------
if self.is_overridden('training_epoch_end', model=model):
self.global_step += 1
# remove the protected keys so the user doesn't have to deal with them
if is_result_obj:
epoch_output = epoch_output[0].__class__.gather(epoch_output)
# run training_epoch_end
epoch_output = model.training_epoch_end(epoch_output)
if isinstance(epoch_output, Result):
epoch_log_metrics = epoch_output.epoch_log_metrics
epoch_progress_bar_metrics = epoch_output.epoch_pbar_metrics
else:
_processed_outputs = self.process_output(epoch_output)
epoch_progress_bar_metrics = _processed_outputs[1]
epoch_log_metrics = _processed_outputs[2]
epoch_callback_metrics = _processed_outputs[3]
# --------------------------
# Structured Result (auto epoch end)
# --------------------------
elif is_result_obj:
epoch_output = epoch_output[0].__class__.reduce_on_epoch_end(epoch_output)
epoch_output.minimize = epoch_output.minimize.mean()
epoch_log_metrics = epoch_output.epoch_log_metrics
epoch_progress_bar_metrics = epoch_output.epoch_pbar_metrics
# --------------------------
# track results
# --------------------------
# add the metrics to the loggers
if epoch_log_metrics and len(epoch_log_metrics) > 0:
self.log_metrics(epoch_log_metrics, {})
# add metrics to callbacks
self.callback_metrics.update(epoch_callback_metrics)
# add metrics to progress_bar
if len(epoch_progress_bar_metrics) > 0:
self.add_progress_bar_metrics(epoch_progress_bar_metrics)
def sync_horovod(self):
if self.use_horovod:
hvd.join(hvd.local_rank() if self.on_gpu else -1)
def increment_accumulated_grad_global_step(self):
# progress global step according to grads progress
if (self.batch_idx + 1) % self.accumulate_grad_batches == 0:
self.global_step += 1
self.total_batch_idx += 1
def save_train_loop_metrics_to_loggers(self, batch_idx, batch_output):
# when metrics should be logged
should_log_metrics = (batch_idx + 1) % self.row_log_interval == 0 or self.should_stop
if should_log_metrics or self.fast_dev_run:
# logs user requested information to logger
metrics = batch_output.batch_log_metrics
grad_norm_dic = batch_output.grad_norm_dic
if len(metrics) > 0 or len(grad_norm_dic) > 0:
self.log_metrics(metrics, grad_norm_dic)
def save_loggers_in_training_loop(self, batch_idx):
# when loggers should save to disk
should_save_log = (batch_idx + 1) % self.log_save_interval == 0 or self.should_stop
if should_save_log or self.fast_dev_run:
if self.is_global_zero and self.logger is not None:
self.logger.save()
def should_check_val(self, batch_idx, is_last_batch):
# decide if we should run validation
is_val_check_batch = (batch_idx + 1) % self.val_check_batch == 0
can_check_epoch = (self.current_epoch + 1) % self.check_val_every_n_epoch == 0
can_check_val = self.enable_validation and can_check_epoch
should_check_val = is_val_check_batch or self.should_stop
is_last_batch_for_infinite_dataset = (is_last_batch and self.val_check_batch == float('inf'))
should_check_val = can_check_val and (should_check_val or is_last_batch_for_infinite_dataset)
return should_check_val
def run_training_batch(self, batch, batch_idx):
# track grad norms
grad_norm_dic = {}
# track all metrics for callbacks
batch_callback_metrics = []
# track metrics to log
batch_log_metrics = []
using_results_obj = False
if batch is None:
return AttributeDict(signal=0, grad_norm_dic=grad_norm_dic)
# Batch start events
with self.profiler.profile('on_batch_start'):
# callbacks
self.on_batch_start()
# hooks
if self.is_function_implemented('on_batch_start'):
response = self.get_model().on_batch_start(batch)
if response == -1:
return AttributeDict(signal=-1, grad_norm_dic=grad_norm_dic)
splits = [batch]
if self.truncated_bptt_steps is not None:
model_ref = self.get_model()
with self.profiler.profile('tbptt_split_batch'):
splits = model_ref.tbptt_split_batch(batch, self.truncated_bptt_steps)
self.hiddens = None
for split_idx, split_batch in enumerate(splits):
self.split_idx = split_idx
for opt_idx, optimizer in self._get_optimizers_iterable():
# make sure only the gradients of the current optimizer's parameters are calculated
# in the training step to prevent dangling gradients in multiple-optimizer setup.
if len(self.optimizers) > 1:
for param in self.get_model().parameters():
param.requires_grad = False
for group in optimizer.param_groups:
for param in group['params']:
param.requires_grad = True
# -------------------
# calculate loss (train step + train step end)
# -------------------
opt_closure_result = self.optimizer_closure(
split_batch,
batch_idx,
opt_idx,
optimizer,
self.hiddens
)
using_results_obj = isinstance(opt_closure_result.training_step_output, Result)
# ------------------------------
# POST forward bookkeeping
# ------------------------------
batch_callback_metrics.append(opt_closure_result.training_step_output.callback_metrics)
# add metrics to loggers
if using_results_obj:
metrics_to_log = opt_closure_result.training_step_output.batch_log_metrics
else:
metrics_to_log = opt_closure_result.training_step_output.log_metrics
batch_log_metrics.append(metrics_to_log)
# add metrics to progress bar
if using_results_obj:
step_pbar_metrics = opt_closure_result.training_step_output.batch_pbar_metrics
else:
step_pbar_metrics = opt_closure_result.training_step_output.pbar_on_batch_end
if len(step_pbar_metrics) > 0:
self.add_progress_bar_metrics(step_pbar_metrics)
# track hiddens
self.hiddens = opt_closure_result.hiddens
# check if loss or model weights are nan
if self.terminate_on_nan:
self.detect_nan_tensors(opt_closure_result.loss)
# track total loss for logging (avoid mem leaks)
self.batch_loss_value.append(opt_closure_result.loss)
# ------------------------------
# BACKWARD PASS
# ------------------------------
# gradient update with accumulated gradients
if (self.batch_idx + 1) % self.accumulate_grad_batches == 0:
# backward
grad_norm_dic = self.run_batch_backward_pass(split_batch, batch_idx, opt_idx, optimizer)
# calculate running loss for display
self.running_loss.append(self.batch_loss_value.mean() * self.accumulate_grad_batches)
# reset for next set of accumulated grads
self.batch_loss_value.reset()
# Batch end events
with self.profiler.profile('on_batch_end'):
# callbacks
self.on_batch_end()
# model hooks
if self.is_function_implemented('on_batch_end'):
self.get_model().on_batch_end()
# collapse all metrics into one dict
batch_log_metrics = {k: v for d in batch_log_metrics for k, v in d.items()}
# track all metrics for callbacks
if not using_results_obj:
self.callback_metrics.update({k: v for d in batch_callback_metrics for k, v in d.items()})
result = AttributeDict(
signal=0,
grad_norm_dic=grad_norm_dic,
batch_log_metrics=batch_log_metrics,
training_step_output_for_epoch_end=opt_closure_result.training_step_output_for_epoch_end
)
return result
def run_batch_backward_pass(self, split_batch, batch_idx, opt_idx, optimizer):
# ------------------
# GRAD NORMS
# ------------------
# track gradient norms when requested
grad_norm_dic = {}
if batch_idx % self.row_log_interval == 0:
if float(self.track_grad_norm) > 0:
model = self.get_model()
grad_norm_dic = model.grad_norm(
self.track_grad_norm)
# ------------------
# CLIP GRADS
# ------------------
if self.use_amp and NATIVE_AMP_AVALAIBLE and not self.use_tpu:
self.scaler.unscale_(optimizer)
self.clip_gradients()
# ------------------
# .STEP + ZERO_GRAD
# ------------------
self.call_optimizer_step(optimizer, opt_idx, batch_idx, split_batch)
return grad_norm_dic
def call_optimizer_step(self, optimizer, opt_idx, batch_idx, split_batch):
# calls .step(), .zero_grad()
# override function to modify this behavior
model = self.get_model()
with self.profiler.profile('optimizer_step'):
lambda_closure = lambda: self.optimizer_closure(
split_batch,
batch_idx,
opt_idx,
optimizer,
self.hiddens
).loss
# apply TPU optimizer
if self.use_tpu and XLA_AVAILABLE:
model.optimizer_step(self.current_epoch, batch_idx,
optimizer, opt_idx, lambda_closure, on_tpu=True)
# for LBFGS do something a bit different
elif isinstance(optimizer, torch.optim.LBFGS):
# native amp + lbfgs is a no go right now
if self.use_amp and NATIVE_AMP_AVALAIBLE:
raise MisconfigurationException(
'native PyTorch amp and lbfgs are not compatible.'
' To request, please file a Github issue in PyTorch and tag @mcarilli')
model.optimizer_step(self.current_epoch, batch_idx, optimizer, opt_idx, lambda_closure,
using_lbfgs=True)
# when using 16-bit
else:
native_amp = self.use_amp and NATIVE_AMP_AVALAIBLE
model.optimizer_step(self.current_epoch, batch_idx, optimizer, opt_idx, lambda_closure,
using_native_amp=native_amp)
# in native 16-bit we need to update scaler after optimizer step
if self.use_amp and NATIVE_AMP_AVALAIBLE and not self.use_tpu:
self.scaler.update()
# model hook
model.on_before_zero_grad(optimizer)
# clear gradients
model.optimizer_zero_grad(self.current_epoch, batch_idx, optimizer, opt_idx)
def optimizer_closure(self, split_batch, batch_idx, opt_idx, optimizer, hiddens):
"""
wrap the forward step in a closure so second order methods work
"""
# ---------------------------
# FORWARD (TRAINING STEP + TRAIN STEP END)
# ---------------------------
with self.profiler.profile('model_forward'):
if self.use_amp and NATIVE_AMP_AVALAIBLE and not self.use_tpu:
with torch.cuda.amp.autocast():
training_step_output = self.training_forward(split_batch, batch_idx,
opt_idx, hiddens)
else:
training_step_output = self.training_forward(split_batch, batch_idx, opt_idx,
hiddens)
# ----------------------------
# PROCESS THE RESULT
# ----------------------------
# format and reduce outputs accordingly
training_step_output_for_epoch_end = training_step_output
is_result_obj = isinstance(training_step_output, Result)
# don't allow EvalResult in the training_step
if isinstance(training_step_output, EvalResult):
raise MisconfigurationException('training_step cannot return EvalResult, '
'use a dict or TrainResult instead')
# handle regular dicts
if not is_result_obj:
training_step_output = self.process_output(training_step_output, train=True)
training_step_output = AttributeDict(
batch_loss=training_step_output[0],
pbar_on_batch_end=training_step_output[1],
log_metrics=training_step_output[2],
callback_metrics=training_step_output[3],
hiddens=training_step_output[4],
)
# if the user decides to finally reduce things in epoch_end, save raw output without graphs
if isinstance(training_step_output_for_epoch_end, torch.Tensor):
training_step_output_for_epoch_end = training_step_output_for_epoch_end.detach()
elif is_result_obj:
training_step_output_for_epoch_end = copy(training_step_output)
training_step_output_for_epoch_end.detach()
else:
training_step_output_for_epoch_end = recursive_detach(training_step_output_for_epoch_end)
# accumulate loss
# (if accumulate_grad_batches = 1 no effect)
closure_loss = training_step_output.minimize if is_result_obj else training_step_output.batch_loss
closure_loss = closure_loss / self.accumulate_grad_batches
# the loss will get scaled for amp. avoid any modifications to it
untouched_loss = closure_loss.detach().clone()
# backward pass
model_ref = self.get_model()
with self.profiler.profile('model_backward'):
# scale loss for 16 bit
if self.precision == 16 and not self.on_tpu:
closure_loss = model_ref.amp_scale_loss(closure_loss, optimizer, opt_idx)
# enter amp context
if not NATIVE_AMP_AVALAIBLE:
context = closure_loss
closure_loss = closure_loss.__enter__()
# do backward pass
model_ref.backward(self, closure_loss, optimizer, opt_idx)
# exit amp context
if self.precision == 16 and not NATIVE_AMP_AVALAIBLE and not self.on_tpu:
a, b, c = None, None, None
error = context.__exit__(a, b, c)
if error:
rank_zero_warn(a, b, c)
raise Exception('apex unscale error')
# once backward has been applied, release graph
closure_loss = closure_loss.detach()
if is_result_obj:
training_step_output.detach()
else:
training_step_output.batch_loss = training_step_output.batch_loss.detach()
if self.use_horovod:
# Synchronize Horovod to ensure gradient manipulations (e.g., loss scaling) are valid
optimizer.synchronize()
# insert after step hook
if self.is_function_implemented('on_after_backward'):
model_ref = self.get_model()
with self.profiler.profile('on_after_backward'):
model_ref.on_after_backward()
# when in dev debugging track the losses
self.dev_debugger.track_train_loss_history(batch_idx, untouched_loss.detach())
result = AttributeDict(
loss=untouched_loss,
training_step_output=training_step_output,
training_step_output_for_epoch_end=training_step_output_for_epoch_end,
hiddens=training_step_output.hiddens,
)
return result
def _get_optimizers_iterable(self):
if not self.optimizer_frequencies:
# call training_step once per optimizer
return list(enumerate(self.optimizers))
optimizer_freq_cumsum = np.cumsum(self.optimizer_frequencies)
optimizers_loop_length = optimizer_freq_cumsum[-1]
current_place_in_loop = self.total_batch_idx % optimizers_loop_length
# find optimzier index by looking for the first {item > current_place} in the cumsum list
opt_idx = np.argmax(optimizer_freq_cumsum > current_place_in_loop)
return [(opt_idx, self.optimizers[opt_idx])]
# @atexit.register
def run_training_teardown(self):
if hasattr(self, '_teardown_already_run') and self._teardown_already_run:
return
self._teardown_already_run = True
# Train end events
with self.profiler.profile('on_train_end'):
# callbacks
self.on_train_end()
# model hooks
if self.is_function_implemented('on_train_end'):
self.get_model().on_train_end()
if self.logger is not None:
self.logger.finalize("success")
# summarize profile results
if self.global_rank == 0:
self.profiler.describe()
if self.global_rank == 0:
for proc in self.interactive_ddp_procs:
subprocess.Popen.kill(proc)
# clean up dist group
if self.use_ddp or self.use_ddp2:
torch_distrib.destroy_process_group()
# clear mem
if self.on_gpu:
model = self.get_model()
model.cpu()
torch.cuda.empty_cache()
def training_forward(self, batch, batch_idx, opt_idx, hiddens):
"""
Handle forward for each training case (distributed, single gpu, etc...)
:param batch:
:param batch_idx:
:return:
"""
# ---------------
# FORWARD
# ---------------
# enable not needing to add opt_idx to training_step
args = [batch, batch_idx]
if len(self.optimizers) > 1:
if self.has_arg('training_step', 'optimizer_idx'):
args.append(opt_idx)
else:
num_opts = len(self.optimizers)
raise ValueError(
f'Your LightningModule defines {num_opts} optimizers but '
f'training_step is missing the "optimizer_idx" argument.'
)
# pass hiddens if using tbptt
if self.truncated_bptt_steps is not None:
args.append(hiddens)
# distributed forward
if self.use_ddp or self.use_ddp2 or self.use_dp:
output = self.model(*args)
# Horovod
elif self.use_horovod and self.on_gpu:
batch = self.transfer_batch_to_gpu(batch, hvd.local_rank())
args[0] = batch
output = self.model.training_step(*args)
# single GPU forward
elif self.use_single_gpu:
gpu_id = 0
if isinstance(self.data_parallel_device_ids, list):
gpu_id = self.data_parallel_device_ids[0]
# Don't copy the batch since there is a single gpu that the batch could
# be referenced from and if there are multiple optimizers the batch will
# wind up copying it to the same device repeatedly.
batch = self.transfer_batch_to_gpu(batch, gpu_id)
args[0] = batch
output = self.model.training_step(*args)
# TPU support
elif self.use_tpu:
batch = self.transfer_batch_to_tpu(batch, self.tpu_id)
args[0] = batch
output = self.model.training_step(*args)
# CPU forward
else:
output = self.model.training_step(*args)
# allow any mode to define training_step_end
# do something will all the dp outputs (like softmax)
if self.is_overridden('training_step_end'):
model_ref = self.get_model()
with self.profiler.profile('training_step_end'):
# TODO: modify when using result obj
output = model_ref.training_step_end(output)
# allow any mode to define training_end
# TODO: remove in 1.0.0
if self.is_overridden('training_end'):
model_ref = self.get_model()
with self.profiler.profile('training_end'):
output = model_ref.training_end(output)
rank_zero_warn('`training_end` was deprecated in 0.7.0 and will be removed 1.0.0.'
' Use training_epoch_end instead', DeprecationWarning)
return output
def update_learning_rates(self, interval: str):
"""Update learning rates.
Args:
interval: either 'epoch' or 'step'.
"""
if not self.lr_schedulers:
return
for lr_scheduler in self.lr_schedulers:
current_idx = self.batch_idx if interval == 'step' else self.current_epoch
current_idx += 1 # account for both batch and epoch starts from 0
# Take step if call to update_learning_rates matches the interval key and
# the current step modulo the schedulers frequency is zero
if lr_scheduler['interval'] == interval and current_idx % lr_scheduler['frequency'] == 0:
# If instance of ReduceLROnPlateau, we need to pass validation loss
if lr_scheduler['reduce_on_plateau']:
monitor_key = lr_scheduler['monitor']
monitor_val = self.callback_metrics.get(monitor_key)
if monitor_val is None:
avail_metrics = ','.join(list(self.callback_metrics.keys()))
raise MisconfigurationException(
f'ReduceLROnPlateau conditioned on metric {monitor_key}'
f' which is not available. Available metrics are: {avail_metrics}.'
' Condition can be set using `monitor` key in lr scheduler dict'
)
lr_scheduler['scheduler'].step(monitor_val)
else:
lr_scheduler['scheduler'].step()
def _with_is_last(iterable):
"""Pass through values from the given iterable with an added boolean indicating if this is the last item.
See `https://stackoverflow.com/a/1630350 <https://stackoverflow.com/a/1630350>`_"""
it = iter(iterable)
last = next(it)
for val in it:
# yield last and has next
yield last, False
last = val
# yield last, no longer has next
yield last, True
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