SliM-LLM: Salience-Driven Mixed-Precision Quantization for Large Language Models
<|reference_start|>SliM-LLM: Salience-Driven Mixed-Precision Quantization for Large Language Models: Large language models (LLMs) achieve remarkable performance in natural language understanding but require substantial computation and memory resources. Post-training quantization (PTQ) is a powerful compression technique extensively investigated in LLMs. However, existing PTQ methods are still not ideal in terms of accuracy and efficiency, especially with below 4 bit-widths. Standard PTQ methods using group-wise quantization suffer difficulties in quantizing LLMs accurately to such low-bit, but advanced methods remaining high-precision weights element-wisely are hard to realize their theoretical hardware efficiency. This paper presents a Salience-Driven Mixed-Precision Quantization scheme for LLMs, namely SliM-LLM. The scheme exploits the salience distribution of weights to determine optimal bit-width and quantizers for accurate LLM quantization, while aligning bit-width partition to groups for compact memory usage and fast integer inference. Specifically, the proposed SliM-LLM mainly relies on two novel techniques: (1) Salience-Determined Bit Allocation utilizes the clustering characteristics of salience distribution to allocate the bit-widths of each group, increasing the accuracy of quantized LLMs and maintaining the inference efficiency; (2) Salience-Weighted Quantizer Calibration optimizes the parameters of the quantizer by considering the element-wise salience within the group, balancing the maintenance of salient information and minimization of errors. Comprehensive experiments show that SliM-LLM significantly improves the accuracy of LLMs at ultra-low bits, e.g., 2-bit LLaMA-7B achieves a 5.5-times memory-saving than original model on NVIDIA A800 GPUs, and 48% decrease of perplexity compared to the state-of-the-art gradient-free PTQ method. Moreover, SliM-LLM+, which is integrated from the extension of SliM-LLM with gradient-based quantizers, further reduces perplexity by 35.1%.<|reference_end|>
@article{huang2024slim-llm:,
    title={SliM-LLM: Salience-Driven Mixed-Precision Quantization for Large
  Language Models},
    author={Wei Huang, Haotong Qin, Yangdong Liu, Yawei Li, Xianglong Liu, Luca
  Benini, Michele Magno, Xiaojuan Qi},
    journal={arXiv preprint arXiv:2405.14917},
    year={2024},
    archivePrefix={arXiv},
    eprint={2405.14917},
    primaryClass={cs.LG cs.CL}
}