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, 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 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.