vLLM是一款专为大规模语言模型(LLM)设计的高性能开源推理与服务引擎,通过一系列底层系统级优化,实现了极高的推理吞吐量和内存效率,是部署和加速大模型的关键工具。 
🔧 核心技术与工作原理
vLLM的性能飞跃主要源于以下两项关键技术:
PagedAttention (分页注意力):这是vLLM的核心技术。它借鉴了操作系统的虚拟内存分页思想,将模型推理时占主要显存的键值(KV)缓存,划分为固定大小的“块”。这允许:
- 高效的内存共享:来自不同请求的令牌可以动态、紧凑地存储在物理显存中,显著减少了内存碎片。
- 灵活的内存分配:可以按需分配和释放KV缓存块,无需为每个序列预分配最大长度的内存,从而支持更长的上下文和更高的并发。
Continuous Batching (连续批处理):传统批处理需要等一个批次的所有请求都完成后才能开始下一批。vLLM的连续批处理则能动态管理一个请求队列:
- 动态插入:新请求到达时,可立即加入当前正在处理的批次。
- 即时释放:批次中某个请求生成完毕后,其占用的计算资源可立即释放给队列中的其他请求。
- 这项技术确保了GPU时刻处于高负载状态,极大地提升了吞吐量,尤其在高并发场景下优势明显。
下图展示了一个典型请求在vLLM引擎中的处理流程,以及上述核心技术如何发挥作用:
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