Network Stack Specialization for Performance

摘要

Contemporary network stacks are masterpieces of generality, supporting many edge-node and middle-node functions. Generality comes at a high performance cost: current APIs, memory models, and implementations drastically limit the effectiveness of increasingly powerful hardware. Generality has historically been required so that individual systems could perform many functions. However, as providers have scaled services to support millions of users, they have transitioned toward thousands (or millions) of dedicated servers, each performing a few functions. We argue that the overhead of generality is now a key obstacle to effective scaling, making specialization not only viable, but necessary. We present Sandstorm and Namestorm, web and DNS servers that utilize a clean-slate userspace network stack that exploits knowledge of application-specific workloads. Based on the netmap framework, our novel approach merges application and network-stack memory models, aggressively amortizes protocol-layer costs based on application-layer knowledge, couples tightly with the NIC event model, and exploits microarchitectural features. Simultaneously, the servers retain use of conventional programming frameworks. We compare our approach with the FreeBSD and Linux stacks using the nginx web server and NSD name server, demonstrating 2-10× and 9× improvements in web-server and DNS throughput, lower CPU usage, linear multicore scaling, and saturated NIC hardware.