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How To Finetune GPT Like Large Language Models on a Custom Dataset


Learn how to fine-tune large language models (LLMs) on a custom dataset. We will be using Lit-Parrot, a nanoGPT based implementation of the GPT-NeoX
model that supports – StableLM, Pythia, and RedPajama-INCITE model weights.

The AI community’s effort has led to the development of many high-quality open-source LLMs, including but not limited to Open LLaMA, StableLM, and Pythia. You can fine-tune these models on a custom instruction dataset to adapt to your specific task, such as training a chatbot to answer financial questions.

Lightning AI recently launched Lit-Parrot, the second LLM implementation in the Lit-* series. The goal of these Lit-* series is to provide the AI/ML community with a clean, solid, and optimized implementation of large language models with pretraining and fine-tuning support using LoRA and Adapter.

We will guide you through the process step by step, from installation to model download and data preparation to fine-tuning. If you have already completed a step or are confident about it, feel free to skip it.

Installing Lit-Parrot 🦜

The Lit-Parrot repository is available in the Lightning AI Github organization here. To get started, clone the repository and install its dependencies.

git clone <>
cd lit-parrot

We are using FlashAttention, a fast and memory-efficient implementation of attention, which is only available in PyTorch Nightly 2.1 at the moment of writing this article.

# for cuda
pip install --index-url <> --pre 'torch>=2.1.0dev' # for cpu
pip install --index-url <> --pre 'torch>=2.1.0dev'

Finally, install the dependencies using pip install -r requirements.txt .

Downloading the model weights

In order to use the model or fine-tune it we need a pre-trained weight. Thanks to the effort of open source teams, we have a bunch of open source weights that we can use for commercial purposes. Lit-Parrot being a GPT NeoX implementation
supports StableLM, Pythia, and RedPajama-INCITE weights. We use the RedPajama-INCITE 3B parameter weights in this tutorial. You can find the instructions to download other weights in this howto section.

# download the model weights
python scripts/ --repo_id togethercomputer/RedPajama-INCITE-Base-3B-v1 # convert the weights to Lit-Parrot format
python scripts/ --checkpoint_dir checkpoints/togethercomputer/RedPajama-INCITE-Base-3B-v1

You will see, gpt_neox layers being mapped to the Lit-Parrot layers in the terminal. After this step, you can find the downloaded weights in the checkpoints/togethercomputer/RedPajama-INCITE-Base-3B-v1 folder.

Prepare the dataset

In this tutorial, we will use the Dolly 2.0 instruction dataset by Databricks for fine-tuning. Finetuning involves two main steps- first, we process the dataset in the Lit-Parrot format and then we run the fine-tuning script on the processed dataset.

Instruction datasets typically have three keys: instruction, input (optional context for the given instruction), and the expected response from the LLM. Below is a sample example of instruction data:

"instruction": "Arrange the given numbers in ascending order.",
"input": "2, 4, 0, 8, 3",
"output": "0, 2, 3, 4, 8"

The dolly 2.0 dataset comes in JSON Lines format, which is plainly speaking a text file with rows of JSON data. It is a convenient format when processing one record at a time. The Dolly dataset contains the following keys –

"instruction": "When did Virgin Australia start operating?",
"context": "Virgin Australia, the trading name of Virgin Australia Airlines Pty Ltd, is an Australian-based airline. It is the largest airline by fleet size to use the Virgin brand. It commenced services on 31 August 2000 as Virgin Blue, with two aircraft on a single route. It suddenly found itself as a major airline in Australia's domestic market after the collapse of Ansett Australia in September 2001. The airline has since grown to directly serve 32 cities in Australia, from hubs in Brisbane, Melbourne and Sydney.",
"response": "Virgin Australia commenced services on 31 August 2000 as Virgin Blue, with two aircraft on a single route.",
"category": "closed_qa"

We need to rename context to input and response to output and we are all set to process our data.

with open(file_path, "r") as file:
data = file.readlines()
data = [json.loads(line) for line in data]
for item in data:
item["input"] = item.pop("context")
item["output"] = item.pop("response")

We can modify the existing Alpaca script for our data preparation. This script downloads data from tloen’s Alpaca-lora project and saves the processed data. It includes a prepare function that loads the raw instruction
dataset, creates prompts, and tokenizes them using the model tokenizer provided in the checkpoint_dir. The tokenized data is split into training and test sets based on the test_split_size provided and saved to the destination_path.

To modify the Alpaca script, open it from here and edit the prepare function. This is how our final function would look after mapping the keys appropriately.

DATA_FILE_NAME = "dolly_data_cleaned_archive.json" def prepare(
destination_path: Path = Path("data/dolly"),
checkpoint_dir: Path = Path("checkpoints/togethercomputer/RedPajama-INCITE-Base-3B-v1"),
test_split_size: int = 2000,
max_seq_length: int = 256,
seed: int = 42,
mask_inputs: bool = False, # as in alpaca-lora
data_file_name: str = DATA_FILE_NAME,
) -> None:
"""Prepare the Dolly dataset for instruction tuning. The output is a training and validation dataset saved as `` and ``,
which stores the preprocessed and tokenized prompts and labels.
destination_path.mkdir(parents=True, exist_ok=True)
file_path = destination_path / data_file_name
download(file_path) tokenizer = Tokenizer(checkpoint_dir / "tokenizer.json", checkpoint_dir / "tokenizer_config.json") with open(file_path, "r") as file:
data = file.readlines()
data = [json.loads(line) for line in data]
for item in data:
item["input"] = item.pop("context")
item["output"] = item.pop("response") # Partition the dataset into train and test
train_split_size = len(data) - test_split_size
train_set, test_set = random_split(
data, lengths=(train_split_size, test_split_size), generator=torch.Generator().manual_seed(seed)
train_set, test_set = list(train_set), list(test_set) print(f"train has {len(train_set):,} samples")
print(f"val has {len(test_set):,} samples") print("Processing train split ...")
train_set = [prepare_sample(sample, tokenizer, max_seq_length, mask_inputs) for sample in tqdm(train_set)], file_path.parent / "") print("Processing test split ...")
test_set = [prepare_sample(sample, tokenizer, max_seq_length, mask_inputs) for sample in tqdm(test_set)], file_path.parent / "")

Finally, let’s run the script by providing the data path and the model checkpoint directory.

python scripts/ \
--destination_path data/dolly \
--checkpoint_dir checkpoints/togethercomputer/RedPajama-INCITE-Base-3B-v1

Finetuning the RedPajama-INCITE model

Once you have completed all the above steps, it is straightforward to start fine-tuning. You need to run the script by providing your data path.

python \
--data_dir data/dolly \
--checkpoint_dir checkpoints/togethercomputer/RedPajama-INCITE-Base-3B-v1
--out_dir out/adapter/dolly

You can update the default number of GPUs, micro-batch size, and all the other hyperparameters in the fine-tuning script

You can play with your fine-tuned model using the script by trying different prompts
and turning the model temperature.

python \
--adapter_path out/adapter/dolly/lit_model_adapter_finetuned.pth \
--checkpoint_dir checkpoints/togethercomputer/RedPajama-INCITE-Base-3B-v1 \
--prompt "who is the author of Game of thrones?"

We would love to hear what you have built with Lit-Parrot. Do share us your favorite prompt and response on Twitter or in the Discord community!