提出OSC框架,4比特量化下通过通道分离保护异常值,提升大模型推理精度与效率。
OSC: Hardware Efficient W4A4 Quantization via Outlier Separation in Channel Dimension

- 识别激活异常值在通道维度的固定分布规律,实现精准定位
- 4比特推理时保持平均精度下降仅2.19~1.12点,峰值提速1.78倍
- 适合部署大语言模型的硬件高效4比特量化,尤其适配现代AI加速器
尽管4比特量化对大语言模型的高吞吐部署至关重要,但激活异常值常因低比特格式动态范围受限而导致显著精度下降。本文系统研究异常值的空间分布,发现高幅值异常值在跨令牌时持续占据固定通道,呈现一种令牌持久的结构聚类现象。基于此,提出OSC框架,通过双路径计算实现异常值抑制:推理时并行执行4比特通用矩阵乘法(GEMM)与16比特分支GEMM。具体地,采用离线分组策略识别异常通道,并在线进行结构化子张量提取,将散落的异常通道合并为紧凑密集张量,以规则化且高吞吐的方式实现异常值保护,无缝适配现代4比特微缩硬件。针对W2中异常聚类不明显的输入,引入FP8回退策略。在Qwen3-8B和Qwen3-30B上的评估显示,平均精度下降分别控制在2.19和1.12点以内。值得注意的是,OSC极具硬件友好性,在现代AI加速器上相较W8A8 GEMM基线最高提速1.78倍。
原文摘要 · Abstract (English)
While 4-bit quantization is essential for high-throughput deployment of Large Language Models, activation outliers often lead to significant accuracy degradation due to the restricted dynamic range of low-bit formats. In this paper, we systematically investigate the spatial distribution of outliers and demonstrate a token-persistent structural clustering effect, where high-magnitude outliers consistently occupy fixed channels across tokens. Building on this insight, we propose OSC, a hardware-efficient framework for outlier suppression. During inference, OSC executes a dual-path computation consisting of a low-precision 4-bit General Matrix Multiplication (GEMM) path and a high-precision 16-bit branch GEMM path. Specifically, OSC uses an offline group-wise strategy to identify the channels where outliers are located and then performs structured sub-tensor extraction to coalesce these scattered activation channels into a compact dense tensor online. This mechanism implements outlier protection through regularized and high-throughput GEMM operations, achieving a seamless fit with modern 4-bit micro-scaling hardware. Furthermore, for the inputs of W2 where outlier clustering is less pronounced, we integrate a fallback strategy to FP8. Evaluation on Qwen3-8B and Qwen3-30B restricts the average accuracy drop to 2.19 and 1.12 points, respectively. Notably, OSC is highly hardware-friendly, achieving a peak speedup of 1.78x over the W8A8 GEMM baseline on a modern AI accelerator.
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