DistiLLM: Towards Streamlined Distillation for Large Language Models
Written for the Research library (claude-opus-5-5) from the paper text. Original — arxiv.org/pdf/2402.03898
Summary
DistiLLM tackles knowledge distillation (KD) for auto-regressive language models, where a large teacher LLM is compressed into a smaller student. The authors identify two weaknesses in existing approaches. First, nobody agrees on which loss to use: standard KLD tends to cause mode averaging or collapse, and the best alternative divergence seems to change from task to task. Second, methods that train on student-generated outputs (SGOs) are very slow, because they generate new SGOs at every step. DistiLLM fixes both. It introduces a skew KLD objective, in forward (SKL) and reverse (SRKL) variants, with theoretical backing for stable gradients and small approximation error. It also adds an adaptive off-policy scheme: SGOs go into a replay buffer, and a scheduler raises the probability of using them whenever validation loss gets worse. The method was tested on instruction-following and summarization with GPT-2 and LLaMA teacher–student pairs. Students reach state-of-the-art quality and train 2.5–4.3× faster than MiniLLM and GKD. This makes small, capable LLMs cheaper to build.
Key points
- The two components are the skew KLD loss (SKL/SRKL) and an adaptive SGO scheduler with a replay buffer. The share of SGOs used rises when validation loss increases and the buffered data is reused off-policy. Code is at github.com/jongwooko/distillm (ICML 2024).
- The paper reports that in on-policy methods, producing SGOs takes up to 80% of total training time. DistiLLM's training speedup over MiniLLM and GKD is 2.5–4.3×.
- Teacher–student pairs include GPT-2 XL (1.5B) → GPT-2 (0.1B) and LLaMA-7B → LLaMA-3B. Evaluation covers Dolly Eval, Self-Instruct and Super-Natural.
- When the GPT-2 student starts from a model with no prior fine-tuning, DistiLLM (SRKL) still scores about 26.1 on Dolly Eval. MiniLLM scores about 22.6 and GKD about 23.2 in the same setting, so the method works in a single distillation stage.
- The SGO probability the adaptive scheduler arrives at is within 0.2 (SKL) or 0.1 (SRKL) of the best hand-tuned value, and in most cases it scores better than that value.
Cited by
Cite
@misc{ko2024distillm,
title = {{DistiLLM: Towards Streamlined Distillation for Large Language Models}},
author = {Ko, Jongwoo and Kim, Sungnyun and Chen, Tianyi and Yun, Se-Young},
year = {2024},
doi = {10.48550/arxiv.2402.03898},
eprint = {2402.03898},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2402.03898}
}References
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