91 lines
2.9 KiB
ReStructuredText
91 lines
2.9 KiB
ReStructuredText
:orphan:
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.. _debugging_intermediate:
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###############################
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Debug your model (intermediate)
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###############################
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**Audience**: Users who want to debug their ML code
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----
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***************************
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Why should I debug ML code?
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***************************
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Machine learning code requires debugging mathematical correctness, which is not something non-ML code has to deal with. Lightning implements a few best-practice techniques to give all users, expert level ML debugging abilities.
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----
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**************************************
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Overfit your model on a Subset of Data
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**************************************
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A good debugging technique is to take a tiny portion of your data (say 2 samples per class),
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and try to get your model to overfit. If it can't, it's a sign it won't work with large datasets.
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(See: :paramref:`~lightning.pytorch.trainer.trainer.Trainer.overfit_batches`
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argument of :class:`~lightning.pytorch.trainer.trainer.Trainer`)
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.. testcode::
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# use only 1% of training data (and turn off validation)
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trainer = Trainer(overfit_batches=0.01)
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# similar, but with a fixed 10 batches
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trainer = Trainer(overfit_batches=10)
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When using this argument, the validation loop will be disabled. We will also replace the sampler
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in the training set to turn off shuffle for you.
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----
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********************************
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Look-out for exploding gradients
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********************************
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One major problem that plagues models is exploding gradients.
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Gradient clipping is one technique that can help keep gradients from exploding.
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You can keep an eye on the gradient norm by logging it in your LightningModule:
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.. code-block:: python
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from lightning.pytorch.utilities import grad_norm
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def on_before_optimizer_step(self, optimizer):
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# Compute the 2-norm for each layer
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# If using mixed precision, the gradients are already unscaled here
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norms = grad_norm(self.layer, norm_type=2)
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self.log_dict(norms)
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This will plot the 2-norm of each layer to your experiment manager.
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If you notice the norm is going up, there's a good chance your gradients will explode.
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One technique to stop exploding gradients is to clip the gradient when the norm is above a certain threshold:
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.. testcode::
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# DEFAULT (ie: don't clip)
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trainer = Trainer(gradient_clip_val=0)
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# clip gradients' global norm to <=0.5 using gradient_clip_algorithm='norm' by default
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trainer = Trainer(gradient_clip_val=0.5)
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# clip gradients' maximum magnitude to <=0.5
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trainer = Trainer(gradient_clip_val=0.5, gradient_clip_algorithm="value")
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----
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*************************
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Detect autograd anomalies
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*************************
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Lightning helps you detect anomalies in the PyTorh autograd engine via PyTorch's built-in
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`Anomaly Detection Context-manager <https://pytorch.org/docs/stable/autograd.html#anomaly-detection>`_.
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Enable it via the **detect_anomaly** trainer argument:
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.. testcode::
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trainer = Trainer(detect_anomaly=True)
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