EE-LLM: Early-Exit Large Language Models

EE-LLM is a framework for large-scale training and inference of early-exit (EE) large language models (LLMs), which is built upon Megatron-LM and compatible with 3D parallelism (namely data, tensor, sequence and pipeline parallelism).

As shown in the above figure, an early-exit LLM can convert intermediate hidden states into outputs. During inference, the model can select adaptively one early/final exit to generate the output for each input, without running the full-model forward pass.

Our system supports two methods of training early-exit LLMs:

• Full-parameter training, which updates model parameters by optimizing a weighted sum of losses from multiple exits;
• EE-Tuning, a parameter-efficient approach that augments an existing pre-trained LLM with early-exit layers and tunes them while modules of the original LLM are frozen.

Further details about the usage and functionalities of EE-LLM are introduced in the following.

Installation

The installation of EE-LLM is the same as Megatron-LM. We recommend using the 22.12 version of NGC's PyTorch container (nvcr.io/nvidia/pytorch:22.12-py3), which is also the development environment of EE-LLM.

For more details about the installation of Megatron-LM, please refer to Megatron-LM's README.

Full-parameter training

Below are several example training scripts used in our EE-LLM paper.

# train 1.3B model
./examples/ee_training/1-3B.sh

# train 7B model
./examples/ee_training/7B.sh

# train 13B model 
./examples/ee_training/13B.sh

# train 30B model
./examples/ee_training/30B.sh

The training data used in these scripts can be found in Data-Juicer. You can modify the DATA_PATH environment variable in the scripts to use your own dataset. Note that Megatron-LM can only recognize preprocessed binary data; for more details about Megatron-LM's data preprocessing, please refer to Data Preprocessing

Running the training scripts requires 16 Nvidia A100-80G GPUs or higher hardware specifications. To run them with fewer GPUs, please set the parallelism degrees therein to smaller values.

Below are some new configurations of EE-LLM compared to Megatron-LM. You can customize your own early-exit LLM by modifying these configurations.

Configurations for model architectures

• --exit-layer-nums: indices of the Transformer layers converted to early-exit Transformer layers, starting from 1.

  For example, --exit-layer-nums 6 12 will add early exits to the 6th and 12th Transformer layers.

• --pre-exit: If set, the early-exit modules will be placed before the backbone of the Transformer layer, otherwise they will be placed after the backbone by default.

  For example, the overall model architectures represented by --exit-layer-nums 6 12 and --exit-layer-nums 7 13 --pre-exit are the same.

• --untie-exit-output-weights: If set, each early exit uses a different output word embedding, otherwise all early exits share the same output word embedding.

• --use-exit-norm: If set, add a Norm layer before the early-exit output word embedding.

• --use-exit-mlp: If set, add a MLP layer before the early-exit output word embedding.

• --use-exit-block: If set, add a complete Transformer layer before the early-exit output word embedding.

Configurations for training

• --exit-layer-weight: The targeted loss weights of early exits. Must correspond to --exit-layer-nums one-to-one. Default to 1.0.

• --exit-layer-weight-init: The initial loss weights of early exits, which can be lower or higher than --exit-layer-weight.

• --exit-layer-weight-warmup-iters: The number of warm-up/cool-down iterations for early-exit loss weights (from weight-init to weight), default to 0.

• --exit-layer-weight-warmup-style: The increment function of early-exit loss weights, default to linear.

• --fill-explicit-bubbles: Enable filling explicit bubbles of the 1F1B pipeline schedule with additional microbatches. [Experimental]

• --num-fill-warmup-microbatches: The number of microbatches to be inserted during the warm-up phase of the 1F1B schedule. [Experimental]

• --num-fill-cooldown-microbatches: The number of microbatches to be inserted during the cool-down phase of the 1F1B schedule. [Experimental]

• --backward-forward-ratio: An estimate of the ratio of time consumption between backward and forward computation during training, used to automatically calculate the optimal number of inserted microbatches. Default to 2.0. [Experimental]

EE-Tuning

Before using EE-Tuning, please make sure that the existing LLM checkpoint is in Megatron-LM format. As an example, examples/ee_tuning/convert/convert_llama_hf.sh provides the functionality of converting the Llama 2 HuggingFace checkpoint into Megatron-LM format.

Stage 1: initialize early-exit layers

The first step of EE-Tuning is to use tools/checkpoint/checkpoint_converter.py to add early-exit layers to the standard LLM checkpoint. Example scripts can be found in the following file:

./examples/ee_tuning/convert/add_exit_layers.sh

The relevant arguments are listed below:

• --load-dir: Path to the standard LLM checkpoint in Megatron-LM format.

• --load-iteration: The iteration number of the checkpoint to be loaded.

• --save-dir: Path to the output early-exit LLM checkpoint.

• --add-exit-layer-nums: Indices of the backbone Transformer layers that early exits are added to.

• --use-exit-norm: Add layer normalization (LayerNorm/RMSNorm) to the early-exit layer.

• --use-exit-mlp: Add a MLP to the early-exit layer.

• --use-exit-block: Add a Transformer layer to the early-exit layer.

• --random-init: Initialize model parameters of early-exit layers randomly. Otherwise, they are initialized as duplication of certain modules of the original LLM.

• --megatron-path: Path to EE-LLM root directory.

Stage 2: tune early-exit layers

The second step of EE-Tuning is to tune the early-exit layers of the converted checkpoint, using scripts similar to those for full-parameter training. Below are some example scripts.

# tune Llama 2-Chat 13B with 8 exits
./examples/ee_tuning/tune/llama2_13B_8_exit_mlp_pt.sh

# tune Llama 2-Chat 13B with 1 exit (only load the first 1/4 of the model)
./examples/ee_tuning/tune/llama2_13B_1_exit_mlp_pt.sh

Below are the new parameters relevant to EE-Tuning. Other parameters are the same as those for full-parameter training.

• --tune-exit: Activate the functionality of EE-Tuning.

• --tune-exit-pipeline-parallel-size: Used to support partial checkpoint loading, only load pipeline stages whose stage numbers are not larger than this value.

Inference

We provided a text generation server for inference of early-exit LLMs. To start a server, you can use the following script. Before running, please set CHECKPOINT_PATH to the root folder path of the checkpoint, and set TP and PP appropriately according to the parallelism degrees of the checkpoint.

./examples/ee_inference/ee_inference_server.sh

After the server is started, you can use tools/request_client.py to send requests to the server. Below are some parameters for early-exit LLM inference, which can be found in tools/request_client.py.

• use_early_exit: The early-exit feature is only enabled when this option is set, otherwise the model behaves exactly like a standard model without early exits.

• early_exit_thres: The confidence threshold used to determine whether to execute early exiting, ranging from 0.0 to 1.0.

• exit_layers: Only the early-exit layers listed here will be activated. If empty, all available early-exit layers will be activated.

• print_max_prob: If set, the inference server will print the token with the highest confidence and the confidence values at all exits.

Checkpoints

The model checkpoints used in our EE-LLM paper have been released on ModelScope:

• 1.3B model with two early exits at Layer 6 and 12. [link]
• 7B model with two early exits at Layer 8 and 16. [link]

The provided checkpoints have a pipeline parallel size of 4 (PP=4) and a tensor parallel size of 1 (TP=1), please set those values properly in corresponding scripts. For other parallelism degrees, you can use ./tools/convert_parallelism.sh to convert the checkpoints.

Note: the above checkpoints are pre-trained base model without any fine-tuning or alignment.

BibTeX

@misc{chen2023eellm,
    title={EE-LLM: Large-Scale Training and Inference of Early-Exit Large Language Models with 3D Parallelism},
    author={Yanxi Chen and Xuchen Pan and Yaliang Li and Bolin Ding and Jingren Zhou},
    year={2023},
    eprint={2312.04916},
    archivePrefix={arXiv},
    primaryClass={cs.LG}
}

@misc{pan2024eetuning,
      title={EE-Tuning: An Economical yet Scalable Solution for Tuning Early-Exit Large Language Models}, 
      author={Xuchen Pan and Yanxi Chen and Yaliang Li and Bolin Ding and Jingren Zhou},
      year={2024},
      eprint={2402.00518},
      archivePrefix={arXiv},
      primaryClass={cs.LG}
}