# nanoGPT

The cleanest, fastest repository for training/finetuning medium-sized GPTs.

This repo currently requires reading the code, but it's not that bad. work ongoing...

Getting started:

We need a few dependencies:

- [pytorch](https://pytorch.org), of course
- numpy
- `pip install datasets` for huggingface datasets
- `pip install tiktoken` for OpenAI's fast bpe code
- `pip install wandb` for optional logging

Then we want to render the detaset:

```
$ cd data/openwebtext
$ python prepare.py
```

To download and tokenize the [openwebtext](https://huggingface.co/datasets/openwebtext) dataset. It will create a `train.bin` and `val.bin` which holds the GPT2 BPE token ids in a massive sequence. Then we're ready to kick off training. The training script currently tries to reproduce the smallest GPT-2 released by OpenAI, i.e. the 124M version of GPT-2. We can run it like so:

```
$ python train.py
```

Once some checkpoints are written to the output directory `out`, we're ready to sample from the model:

```
$ python sample.py
```

Training on 1 GPU overnight currently gets loss ~3.74. Random chance at init is -ln(1/50257) = 10.82. Which brings us to baselines.

## baselines

OpenAI GPT-2 checkpoints allow us to get some baselines in place for openwebtext. We can get the numbers as follows:

```
$ python train.py eval_gpt2
$ python train.py eval_gpt2_medium
$ python train.py eval_gpt2_large
$ python train.py eval_gpt2_xl
```

and observe the following losses on train and val:

| model | params | train loss | val loss |
| ------| ------ | ---------- | -------- |
| gpt2 | 124M         | 3.11  | 3.12     |
| gpt2-medium | 350M  | 2.85  | 2.84     |
| gpt2-large | 774M   | 2.66  | 2.67     |
| gpt2-xl | 1558M     | 2.56  | 2.54     |

I briefly tried finetuning gpt2 a bit more on our OWT and didn't notice dramatic improvements, suggesting that OWT is not much much different from WT in terms of the data distribution, but this needs a bit more thorough attempt once the code is in a better place.

## benchmarking

For model benchmarking `bench.py` might be useful. It's identical what happens in `train.py` except we're measuring just the fwd+bwd+update time of the model on a fixed random batch of data.