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Getting Started

This document provides a guide on how to launch model training and configure it according to your specific needs. For an even more detailed guide, please refer to the Levanter Documentation, in particular the Training on Your Own Data page.

Installation

Please see the Installation Guide for more information on how to install Levanter.

Quick Start Examples

{% include-markdown "../README.md" start="" end="" %}

Launch Model Training

To launch the training of a GPT2 model, run the following command:

python src/levanter/main/train_lm.py --config_path config/gpt2_small.yaml

This will execute the training pipeline pre-defined in the train_lm.py and set model and training configuration set in gpt2_small.yaml. You can find more template configurations in the config directory.

Configuration files are processed using Draccus. Draccus is yet-another yaml-to-dataclass library. It should mostly work like you would expect. Arguments may be passed in via the command line using arg-parse style flags like --trainer.num_train_steps, and will override the values in the config file.

Set Custom Training Configuration

In machine learning experiments, it is common to adjust model hyperparameters. In this section, we will provide examples of different use cases and explain the corresponding parameters that you can change.

Change Model Parameters

To change the dimensions of your GPT2 model and increase the number of training steps to 10,000, I can use the following command:

python src/levanter/main/train_lm.py \
    --config_path config/gpt2_small.yaml \
    --model.num_heads 20 \
    --model.num_layers 36 \
    --model.hidden_dim 1280 \
    --trainer.num_train_steps 10000

This will overwrite the default model and training configurations and set the following parameters:

  • model.num_heads: The number of heads in the multi-head attention layers of the transformer encoder and decoder.
  • model.num_layers: The number of layers in the transformer encoder and decoder.
  • model.hidden_dim: The hidden dimension of the model. This is the dimension of the hidden states of the transformer encoder and decoder. Note that the hidden dimension must be divisible by the number of heads.
  • trainer.num_train_steps: The number of training steps to run.

You can find a complete list of parameters to change from the TrainerConfig in trainer.py and Gpt2Config in gpt2.py.

Change Checkpoint Settings

To change the frequency of saving checkpoints, you can use the following command:

python src/levanter/main/train_lm.py \
    --config_path config/gpt2_small.yaml \
    --trainer.checkpointer.base_path checkpoints/gpt2/ \
    --trainer.checkpointer.save_interval 20m

This will overwrite the default checkpoint settings from the TrainerConfig and CheckpointerConfig in checkpoint.py to save checkpoints every 20 minutes. The checkpoint will be saved to the directory checkpoints/gpt2/${run_id}

Note that:

  • --trainer.checkpointer.base_path supports local path and cloud storage path (e.g. S3, GCS, etc.), as long as the path is accessible from the machine that you are running the training script on.
  • The --trainer.checkpointer.save_interval argument supports the following units: s (seconds), m (minutes), h (hours), d (days).
  • You can also specify --trainer.load_checkpoint_path to load a checkpoint from a specific path. If you do not specify it, the trainer will see if the {checkpointer.base_path}/{run_id} directory exists and load the latest checkpoint from there. If the directory does not exist, the trainer will start training from scratch.
  • You can also specify --trainer.initialize_from to initialize the model from a specific checkpoint, without loading the optimizer state.

Change Evaluation Parameters

To change how often the model is evaluated during training, you can use the following command:

python src/levanter/main/train_lm.py \
    --config_path config/gpt2_small.yaml \
    --trainer.steps_per_eval 500

This will overwrite the default eval frequency (every 1,000) from the TrainerConfig in config.py to every 500 steps.

Change Parallelism Settings

By default, Levanter will split the number of examples in train_batch_size equally across all available GPUs. To set explicit number of examples to process on each device during training and evaluation, you can use the following command:

python src/levanter/main/train_lm.py \
    --config_path config/gpt2_small.yaml \
    --trainer.batch_size 256 \
    --trainer.per_device_parallelism 64 \
    --trainer.eval_per_device_parallelism 64

Note that:

  • batch_size must be divisible by per_device_parallelism and eval_per_device_parallelism.
  • If num_devices * per_device_parallelism is smaller than batch_size, we use gradient accumulation to accumulate gradients from multiple batches before performing a parameter update. This is useful when you have a large batch size but do not have enough memory to fit the entire batch.

Change WandB Configuration

Levanter supports extensive logging, metrics tracking, and artifact saving on WandB. Once you have created a WandB account and finished setting up your WandB API key, all of your training runs will be automatically logged to WandB, without any additional configuration in your training commands.

Suppose you want to set more control on your WandB logging, you can use the following command:

python src/levanter/main/train_lm.py \
    --config_path config/gpt2_small.yaml \
    --trainer.wandb.project my_project \
    --trainer.wandb.name my_run \
    --trainer.wandb.group my_new_exp_group

This will overwrite the default WandB configuration from the TrainerConfig in config.py. We pass all these arguments to the wandb.init() function at the same verbatim. For more information on the WandB configuration, please refer to the WandB documentation.

Resume Training Runs

When you resume a training run, you may like to restart from a previously saved checking and resume the corresponding WandB run, as well. To do so, you can use the following command. The trainer.wandb.resume true is optional, but will make WandB error out if the run ID does not exist.

python src/levanter/main/train_lm.py \
    --config_path config/gpt2_small.yaml \
    --trainer.wandb.resume true \
    --trainer.id asdf1234

There are two things to note here:

  1. Resume from a checkpoint: as we stated in a section above, the --trainer.load_checkpoint_path argument is optional. If it is specified, the trainer will recursively search for the latest checkpoint in the directory and load it. If you do not specify it, the trainer will start training from scratch.
  2. Resume from a WandB run: if you set --trainer.wandb.resume, it will resume the corresponding WandB run with the ID asdf1234. You can find the WandB run ID in the URL of your WandB run page. For more information, please refer to the WandB documentation.