GPT is a decoder-only Transformer model.
The steps below demonstrate training of a GPT-style model with NeMo
This example is best completed using the latest NeMo Framework NGC Container
Data download & pre-processing
Data download, pre-processing and tokenizer training in the example below will take ~3 hours.
Step 1: Download data
The step below will download Wikipedia data (around 20GB) and can take several hours.
wget https://dumps.wikimedia.org/enwiki/latest/enwiki-latest-pages-articles.xml.bz2
Step 2: Extract raw data
pip install wikiextractor
python -m wikiextractor.WikiExtractor enwiki-latest-pages-articles.xml.bz2 --json
find text -name 'wiki_*' -exec cat {} \; > train_data.jsonl
Now, train_data.jsonl will contain our training data in the json line format. We are interested in the data under “text” field.
Step 3: Train tokenizer
Below we will consider 2 options for training data tokenizers: Using pre-built HuggingFace BPE and training and using your own Google Sentencepiece tokenizer.
Note that only the second option allows you to experiment with vocabulary size.
Option 1: Using HuggingFace GPT2 tokenizer files.
With this option, we will download a pre-built vocabulary and merge the files for the BPE tokenizer.
wget https://s3.amazonaws.com/models.huggingface.co/bert/gpt2-vocab.json
wget https://s3.amazonaws.com/models.huggingface.co/bert/gpt2-merges.txt
Option 2: Using Google Sentencepiece tokenizer library.
It comes as a dependency with NeMo, so if you have installed NeMo it should already be installed. Note that training tokenizer model will also take some time.
sudo apt install jq
jq .text train_data.jsonl >> text_for_tokenizer.txt
spm_train --input=text_for_tokenizer.txt \
--model_prefix=spm_32k_wiki \
--vocab_size=32768 \
--character_coverage=0.9999 \
--model_type=bpe \
--byte_fallback=true \
--pad_id=0 --unk_id=1 --bos_id=2 --eos_id=3 \
--split_digits true
After this is done (will take a while), you’ll have two files: `spm_32k_wiki.model` and ```spm_32k_wiki.vocab``corresponding to the model and vocabulary.
Step 4: Convert training data into memory map format
This format makes training more efficient, especially with many nodes and GPUs. This step will also tokenize data using the tokenizer model from Step 3.
Option 1: Using HuggingFace GPT2 tokenizer files.
python <NeMo_ROOT_FOLDER>/scripts/nlp_language_modeling/preprocess_data_for_megatron.py \
--input=train_data.jsonl \
--json-keys=text \
--tokenizer-library=megatron \
--vocab gpt2-vocab.json \
--dataset-impl mmap \
--tokenizer-type GPT2BPETokenizer \
--merge-file gpt2-merges.txt \
--output-prefix=hfbpe_gpt_training_data \
--append-eod \
--workers=32
Option 2: Using Google Sentencepiece tokenizer library.
python <NeMo_ROOT_FOLDER>/scripts/nlp_language_modeling/preprocess_data_for_megatron.py \
--input=train_data.jsonl \
--json-keys=text \
--tokenizer-library=sentencepiece \
--tokenizer-model=spm_32k_wiki.model \
--output-prefix=gpt_training_data \
--append-eod \
--workers=32
Train GPT-style Model
Once you have prepared training data and tokenizer, you are ready to train the model. The configuration we present below has about 124M parameters and should fit on a single 16GB GPU using float16. Let’s go!
Option 1: Using HuggingFace GPT2 tokenizer files.
python <NeMo_ROOT_FOLDER>/examples/nlp/language_modeling/megatron_gpt_pretraining.py \
--config-path=<NeMo_ROOT_FOLDER>/examples/nlp/language_modeling/conf \
--config-name=megatron_gpt_config \
trainer.devices=1 \
trainer.num_nodes=1 \
trainer.max_epochs=null \
trainer.max_steps=300000 \
trainer.val_check_interval=300 \
trainer.log_every_n_steps=50 \
trainer.limit_val_batches=50 \
trainer.limit_test_batches=50 \
trainer.accumulate_grad_batches=1 \
trainer.precision=16 \
model.micro_batch_size=6 \
model.global_batch_size=192 \
model.tensor_model_parallel_size=1 \
model.pipeline_model_parallel_size=1 \
model.max_position_embeddings=1024 \
model.encoder_seq_length=1024 \
model.hidden_size=768 \
model.ffn_hidden_size=3072 \
model.num_layers=12 \
model.num_attention_heads=12 \
model.init_method_std=0.021 \
model.hidden_dropout=0.1 \
model.layernorm_epsilon=1e-5 \
model.tokenizer.vocab_file=gpt2-vocab.json \
model.tokenizer.merge_file=gpt2-merges.txt \
model.data.data_prefix=[1.0,hfbpe_gpt_training_data_text_document] \
model.data.num_workers=2 \
model.data.seq_length=1024 \
model.data.splits_string=\'980,10,10\' \
model.optim.name=fused_adam \
model.optim.lr=6e-4 \
model.optim.betas=[0.9,0.95] \
model.optim.weight_decay=0.1 \
model.optim.sched.name=CosineAnnealing \
model.optim.sched.warmup_steps=750 \
model.optim.sched.constant_steps=80000 \
model.optim.sched.min_lr=6e-5 \
exp_manager.resume_if_exists=True \
exp_manager.resume_ignore_no_checkpoint=True \
exp_manager.create_checkpoint_callback=True \
exp_manager.checkpoint_callback_params.monitor=val_loss \
exp_manager.checkpoint_callback_params.save_top_k=3 \
exp_manager.checkpoint_callback_params.mode=min \
exp_manager.checkpoint_callback_params.always_save_nemo=False
Option 2: Using Google Sentencepiece tokenizer library.
python <NeMo_ROOT_FOLDER>/examples/nlp/language_modeling/megatron_gpt_pretraining.py \
--config-path=<NeMo_ROOT_FOLDER>/examples/nlp/language_modeling/conf \
--config-name=megatron_gpt_config \
trainer.devices=1 \
trainer.num_nodes=1 \
trainer.max_epochs=null \
trainer.max_steps=300000 \
trainer.val_check_interval=300 \
trainer.log_every_n_steps=50 \
trainer.limit_val_batches=50 \
trainer.limit_test_batches=50 \
trainer.accumulate_grad_batches=1 \
trainer.precision=16 \
model.micro_batch_size=6 \
model.global_batch_size=192 \
model.tensor_model_parallel_size=1 \
model.pipeline_model_parallel_size=1 \
model.max_position_embeddings=1024 \
model.encoder_seq_length=1024 \
model.hidden_size=768 \
model.ffn_hidden_size=3072 \
model.num_layers=12 \
model.num_attention_heads=12 \
model.init_method_std=0.021 \
model.hidden_dropout=0.1 \
model.layernorm_epsilon=1e-5 \
model.tokenizer.library=sentencepiece \
model.tokenizer.model=spm_32k_wiki.model \
model.data.data_prefix=[1.0,gpt_training_data_text_document] \
model.data.num_workers=2 \
model.data.seq_length=1024 \
model.data.splits_string=\'980,10,10\' \
model.optim.name=fused_adam \
model.optim.lr=6e-4 \
model.optim.betas=[0.9,0.95] \
model.optim.weight_decay=0.1 \
model.optim.sched.name=CosineAnnealing \
model.optim.sched.warmup_steps=750 \
model.optim.sched.constant_steps=80000 \
model.optim.sched.min_lr=6e-5 \
exp_manager.resume_if_exists=True \
exp_manager.resume_ignore_no_checkpoint=True \
exp_manager.create_checkpoint_callback=True \
exp_manager.checkpoint_callback_params.monitor=val_loss \
exp_manager.checkpoint_callback_params.save_top_k=3 \
exp_manager.checkpoint_callback_params.mode=min \
exp_manager.checkpoint_callback_params.always_save_nemo=False
Next, you can launch Tensorboard to monitor training like so:
tensorboard --logdir nemo_experiments --bind_all
Next steps
Please refer to:
Batching section for batch size adjustments
Parallelisms section for understanding various types of parallelisms
promptlearning section for details on prompt-tuning and p-tuning