Knowledge distillation (KD) is known as a promising solution to compress large language models (LLMs) via transferring their knowledge to smaller models. During this process, white-box KD methods usually minimize the distance between the output distributions of the two models so that more knowledge can be transferred. However, in the current white-box KD framework, the output distributions are from the respective output spaces of the two models, using their own prediction heads. We argue that the space discrepancy will lead to low similarity between the teacher model and the student model on both representation and distribution levels. Furthermore, this discrepancy also hinders the KD process between models with different vocabularies, which is common for current LLMs. To address these issues, we propose a dual-space knowledge distillation (DSKD) framework that unifies the output spaces of the two models for KD. On the basis of DSKD, we further develop a cross-model attention mechanism, which can automatically align the representations of the two models with different vocabularies. Thus, our framework is not only compatible with various distance functions for KD (e.g., KL divergence) like the current framework, but also supports KD between any two LLMs regardless of their vocabularies. Experiments on task-agnostic instruction-following benchmarks show that DSKD significantly outperforms the current white-box KD framework with various distance functions, and also surpasses existing KD methods for LLMs with different vocabularies.

通过提出双空间知识蒸馏 (DSKD) 框架，我们解决了当前白盒知识蒸馏框架中不同模型之间输出空间差异导致的问题，并进一步开发了跨模型注意力机制，支持具有不同词汇的任意两个大语言模型之间的知识蒸馏。实验证明，DSKD在各种距离函数下显著优于当前白盒知识蒸馏框架，并且超过了现有的具有不同词汇的大语言模型的其他知识蒸馏方法。

大型语言模型的双空间知识蒸馏