Response Length Perception & Sequence Scheduling

Description

PyTorch implementation of paper "Response Length Perception and Sequence Scheduling: An LLM-Empowered LLM Inference Pipeline". [blog]

We find that large language models (LLMs) have the remarkable ability to perceive the length of their generated responses in advance. Leveraging this LLM ability, we propose a novel technique called Sequence Scheduling to improve the efficiency of LLM batch inference. By grouping queries with similar perceived response lengths together, we significantly reduce redundant computations and achieve an impressive 86% improvement in inference throughput without compromising performance.

Perception in Advance (PiA)

Perception in advance asks LLM to perceive the length of the response in advance. LLMs (e.g. ChatGPT) have the ability to conduct this task.

Perceived length: 10, real length: 6.

Perceived length: 112, real length: 119.

Requirement

Install the required packages.
```
pip install -r requirements.txt
```
Get the original LLaMA weights in the Hugging Face format by following the instructions here.

Get the Vicuna-7B weights by following the instructions here

python3 -m fastchat.model.apply_delta \
--base-model-path ./ckpts/llama-7b \
--target-model-path ./ckpts/vicuna-7b \
--delta-path lmsys/vicuna-7b-delta-v1.1

Response Length Perception

(Optional) Data Preparation: use the following command to generate alpaca-train-10k.json and alpaca-val-10k.json, or use the data in data folder directly.
```
python3 -m src.sample
```
(Optional) Collect the training dataset: first, use the following command to perform multiple inference for the training dataset, or use alpaca-train-10k-length.json directly.
```
CUDA_VISIBLE_DEVICES=0 python -m src.lenpred
```
Then, use the following command to construct the training dataset for instruction tunning, or use alpaca-train-10k-instruct.json directly.
```
python3 -m src.construct
```
Instruction Tunning: use the following command to perform instruction tunning.
```
bash train.sh
```
or you can download the LoRA weight from huggingface ckpts/vicuna-response-length-perception-module.
```
git clone https://huggingface.co/zangwei/vicuna-response-length-perception-module ckpts/vicuna-response-length-perception-module
```
(Optional) Evaluation: use the following command to evaluate the length perception performance.
```
CUDA_VISIBLE_DEVICES=0 python3 -m src.eval
```
- Error: 62
- Acc-50: 59%
- Acc-100: 81%

Sequence Scheduling

Run following commands to benchmark different inference strategy.

Vanilla: no scheduling.
- Throughput: 1.39 samples/s
- Average length: 370.84 tokens
- Effective token ratio: 33.91%

CUDA_VISIBLE_DEVICES=0 python -m src.benchmark --num-data 1024

Sequence scheduling: with the instruction-tuned response length perception module, and VBS and FCR strategy.
- Throughput: 2.30 samples/s
- Average length: 215.06 tokens
- Effective token ratio: 47.22%
- FCR ratio: 16.50 %

CUDA_VISIBLE_DEVICES=0 python -m src.benchmark --num-data 1024 --strategy seqsch --vbs --fcr --lora-path ./ckpts/vicuna-response-length-perception-module

Sequence scheduling: with the instruction-tuned response length perception module, without VBS and FCR strategy.
- Throughput: 1.64 samples/s
- Average length: 297.48 tokens
- Effective token ratio: 42.17 %

CUDA_VISIBLE_DEVICES=0 python -m src.benchmark --num-data 1024 --strategy seqsch --lora-path ./ckpts/vicuna-response-length-perception-module

Sequence scheduling: with Perception Only for length prediction. VBS and FCR degrade the performance so we do not use them here.
- Throughput: 1.32 samples/s
- Average length: 374.83 tokens
- Effective token ratio: 33.53 %

CUDA_VISIBLE_DEVICES=0 python -m src.benchmark --num-data 1024 --strategy po

Sequence scheduling: with ground truth as an upper bound of the performance. VBS and FCR are used here.
- Time: Throughput: 2.69 samples/s
- Average length: 196.34 tokens
- Effective token ratio: 61.57 %

CUDA_VISIBLE_DEVICES=0 python -m src.benchmark --num-data 1024 --strategy gt --vbs --fcr

Citation

@article{zheng2023response,
    title={Response Length Perception and Sequence Scheduling: An LLM-Empowered LLM Inference Pipeline},
    author={Zangwei Zheng and Xiaozhe Ren and Fuzhao Xue and Yang Luo and Xin Jiang and Yang You},
    journal={arXiv preprint arXiv:2305.13144},
    year={2023}
}