The Llama-2 family of models are an open-source set of pretrained & finetuned (for chat) models that have achieved strong results across a wide set of benchmarks. At the time of release, Llama-2 models achieved among the best results for open-source models, and were competitive with the closed-source GPT-3.5 model (see https://arxiv.org/pdf/2307.09288.pdf).
Llama-2 checkpoints can be loaded into Megatron for inference and for finetuning. Loading these checkpoints consists of three steps:
- Get access to download the checkpoints.
- Convert the checkpoints from Meta/Huggingface format to Megatron format.
- Setup arguments for launching the model.
The following sections detail these steps. The final section lists benchmark result comparisons between: 1) Llama-2 inference code running the Meta-format checkpoints, and 2) Megatron inference code running the converted checkpoints.
Users must first apply for access to download the Llama-2 checkpoints either directly from Meta or through Huggingface (HF). The checkpoints are available in two formats, Meta's native format (available from both the Meta and HF links), and HF's format (available only from HF). Either format can be converted to Megatron, as detailed next.
Depending on which checkpoint format is downloaded (Meta or HF), one or two steps must be taken to convert to Megatron format.
The Meta format checkpoints must first be converted to HF format before converting to Megatron format. The transformers package is required for the first step, and must have version >=4.31.0 (e.g., pip install transformers>=4.31.0). (Note: we have specifically tested with versions 4.31.0 and 4.32.0; your experience may vary with newer versions.) Assuming the downloaded checkpoints are in $CHECKPOINT_DIR (with separate sub-directories for 7B, 13B, 70B, etc.), the following example command can be used to convert from Llama-2 format to HF format:
$>: python $LIB_DIR/transformers/models/llama/convert_llama_weights_to_hf.py \
> --input_dir $LLAMA_FORMAT_DIR \
> --output_dir $HF_FORMAT_DIR \
> --model_size 7B`
Valid values for --model_size include 7B, 13B, and 70B (for pretrained-only models), and 7Bf, 13Bf, and 70Bf (for chat-finetuned models). Use python convert_llama_weights_to_hf.py --help for additional argument details. Once the checkpoints have been converted to HF format, proceed to the Huggingface format section below.
The HF checkpoints can be converted to Megatron format by using Megatron's own Llama-2 checkpoint converter for HF format (see script tools/checkpoint/loader_llama2_hf.py). One important argument that must be set correctly is the tensor parallel size (TP) for each model. The following table shows these values:
| Model size | Tensor parallel size (TP) |
|---|---|
| 7B | 1 |
| 13B | 2 |
| 70B | 8 |
Using these values for TP, along with the path to the Llama-2 tokenizer model (automatically downloaded with original checkpoint download; see ${TOKENIZER_MODEL} below), run the following command from the root of your Megatron source code to convert from HF format to Megatron format:
$>: python tools/checkpoint/util.py \
> --model-type GPT \
> --loader llama2_hf \
> --saver megatron \
> --target-tensor-parallel-size ${TP} \
> --load-dir ${HF_FORMAT_DIR} \
> --save-dir ${MEGATRON_FORMAT_DIR} \
> --tokenizer-model ${TOKENIZER_MODEL}
After this conversion, we are ready to load the checkpoints into a Megatron GPT model.
If loading for either inference or finetuning, use the following arguments:
--tensor-model-parallel-size ${TP} \
--pipeline-model-parallel-size 1 \
--seq-length 4096 \
--max-position-embeddings 4096 \
--tokenizer-type Llama2Tokenizer \
--tokenizer-model ${TOKENIZER_MODEL} \
--load ${CHECKPOINT_DIR} \
--exit-on-missing-checkpoint \
--use-checkpoint-args \
--no-load-optim \
--no-load-rng \
--fp16 \
--untie-embeddings-and-output-weights \
--use-rotary-position-embeddings \
--normalization RMSNorm \
--no-position-embedding \
--no-masked-softmax-fusion \
Meta checkpoints can be launched with: https://github.com/facebookresearch/llama
Huggingface checkpoints can be launched with: https://github.com/huggingface/transformers/blob/main/src/transformers/models/llama/modeling_llama.py
The tables below list the benchmark comparisons between native Llama-2 (using Meta's checkpoint and Meta's inference code) and Megatron (using a converted HF checkpoint and Megatron's inference code).
The values are the percent error between Megatron and Llama-2, calculated using the formula: |<llama_score> - <megatron_score>| / <llama_score>, where the type of score is detailed before each table. Across all tests (80 total per model size), the mean error is 0.15%. The small difference in benchmark scores between the two models is due to minor arithmetic differences in implementation that alter the numerics slightly. Some of the factors that influence this difference include:
- Megatron performs batch matrix multiplications in a couple places, such as within self attention and in SwiGLU, that Llama performs separately.
- Megatron uses
torch.baddbmmwithin self attention, versus Llama usingtorch.matmul. - Megatron uses a
sin/cosimplementation for rotary position embeddings, versus Llama using apolar/compleximplementation. - Llama calls
torch.set_default_dtype(torch.float16)during initialization, which Megatron does not.
Score type: multiple choice grade.
| bigbench / standard | 7b | 13b | 70b |
|---|---|---|---|
| date_understanding | 0.29% | 0.13% | 0.12% |
| general_knowledge | 0.00% | 0.00% | 0.00% |
| human_organs_senses | 0.00% | 0.00% | 0.00% |
| intent_recognition | 0.00% | 0.11% | 0.00% |
| riddle_sense | 0.00% | 0.00% | 0.00% |
| similarities_abstraction | 0.00% | 0.58% | 0.00% |
| simple_arithmetic_json_multiple_choice | 0.00% | 0.00% | 0.00% |
| undo_permutation | 0.19% | 0.19% | 0.18% |
Score type: multiple choice grade.
| multilingual / xcopa | 7b | 13b | 70b |
|---|---|---|---|
| en-template-mGPT-remove-punctuation | 0.08% | 0.00% | 0.00% |
| et-template-mGPT-remove-punctuation | 0.00% | 0.13% | 0.25% |
| ht-template-mGPT-remove-punctuation | 0.26% | 0.13% | 0.26% |
| id-template-mGPT-remove-punctuation | 0.11% | 0.00% | 0.19% |
| it-template-mGPT-remove-punctuation | 0.00% | 0.10% | 0.09% |
| qu-template-mGPT-remove-punctuation | 0.00% | 0.00% | 0.27% |
| sw-template-mGPT-remove-punctuation | 0.14% | 0.13% | 0.13% |
| th-template-mGPT-remove-punctuation | 0.25% | 0.13% | 0.13% |
| tr-template-mGPT-remove-punctuation | 0.26% | 0.00% | 0.34% |
| vi-template-mGPT-remove-punctuation | 0.00% | 0.11% | 0.00% |
| zh-template-mGPT-remove-punctuation | 0.00% | 0.10% | 0.09% |
Score type: multiple choice grade.
| lm-eval | 7b | 13b | 70b |
|---|---|---|---|
| boolq | 0.04% | 0.04% | 0.07% |
| hellaswag | 0.02% | 0.03% | 0.03% |
| piqa | 0.00% | 0.00% | 0.07% |
| winogrande | 0.00% | 0.11% | 0.20% |
Score type: multiple choice grade.
Note: the number in brackets is the number of sub-tasks for each supercategory.
| mmlu | 7b | 13b | 70b |
|---|---|---|---|
| stem [18] | 0.79% | 0.05% | 0.01% |
| humanities [13] | 0.19% | 0.01% | 0.02% |
| other (business, health, misc.) [14] | 0.08% | 0.06% | 0.12% |
| social sciences [12] | 0.37% | 0.21% | 0.01% |