liveBook · Manning

Validation loss

As explained in LLMs in Production

Validation loss is the loss computed on held-out validation examples to assess a model during development.

Validation loss averages loss across validation batches to provide a practical development signal. It is useful for monitoring training, but it is not a complete representation of model performance. section 9.1.2

Estimating validation loss

A loss-evaluation function switches the model to evaluation mode, samples ten batches from the validation split, averages their losses, and then restores training mode.

Use validation loss with deliberate interpretation:

  • Treat the average as a convenient marker, not as a full description of how the model performs. section 9.1.2

How LLMs in Production covers it

How deep it goes
Defines the metric and implements ten-batch averaging, but stops short of treating it as a representative performance measure.
Examples
Uses TinyStories training and validation files plus a PyTorch function that averages ten sampled validation-batch losses.
What it assumes
Assumes prepared training and validation iterators, batching, and a model that returns loss alongside outputs.
What you can do after
Evaluate model behavior during development with a repeatable validation-batch loss estimate.
How it connects
Connects dataset splits, batching, loss, evaluation mode, and inference.

Also explained in

Compare how 5 books explain validation loss →

Related concepts

This explainer was generated by Manning's knowledge graph from the text of LLMs in Production. The section links point to the parts of the book it draws on.