updated early stopping docs (#1410)

* remove incorrect comment in training_step

* added comment for on_batch_start in hooks.py

* update early stopping docs

* typo fix

* whitespace fix

* Apply suggestions from code review

* Update docs/source/early_stopping.rst

Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>

docs/source/early_stopping.rst

@@ -1,15 +1,21 @@
 Early stopping
 ==============
 
-Default behavior
-----------------
+Stopping an epoch early
+-----------------------
+You can stop an epoch early by overriding :meth:`~pytorch_lightning.core.lightning.LightningModule.on_batch_start` to return `-1` when some condition is met.
+
+If you do this repeatedly, for every epoch you had originally requested, then this will stop your entire run.
+
+Default Epoch End Callback Behavior
+-----------------------------------
 By default early stopping will be enabled if `'val_loss'`
 is found in :meth:`~pytorch_lightning.core.lightning.LightningModule.validation_epoch_end`'s
 return dict. Otherwise training will proceed with early stopping disabled.
 
-Enable Early Stopping
----------------------
-There are two ways to enable early stopping.
+Enable Early Stopping using Callbacks on epoch end
+--------------------------------------------------
+There are two ways to enable early stopping using callbacks on epoch end.
 
 .. doctest::
 
@@ -39,8 +45,8 @@ is not defined.
 .. seealso::
     :class:`~pytorch_lightning.trainer.trainer.Trainer`
 
-Disable Early Stopping
-----------------------
+Disable Early Stopping with callbacks on epoch end
+--------------------------------------------------
 To disable early stopping pass ``False`` to the
 :paramref:`~pytorch_lightning.trainer.trainer.Trainer.early_stop_callback`.
 Note that ``None`` will not disable early stopping but will lead to the

pytorch_lightning/core/hooks.py

@@ -51,6 +51,8 @@ class ModelHooks(torch.nn.Module):
     def on_batch_start(self, batch: Any) -> None:
         """Called in the training loop before anything happens for that batch.
 
+        If you return -1 here, you will skip training for the rest of the current epoch.
+
         :param batch:
         """
         # do something when the batch starts

pytorch_lightning/core/lightning.py

@@ -221,9 +221,6 @@ class LightningModule(ABC, GradInformation, ModelIO, ModelHooks):
                         "hiddens": hiddens  # remember to detach() this
                     }
 
-            You can also return a -1 instead of a dict to stop the current loop. This is useful
-            if you want to break out of the current training epoch early.
-
         Notes:
             The loss value shown in the progress bar is smoothed (averaged) over the last values,
             so it differs from the actual loss returned in train/validation step.