Janus: A User-Level TCP Stack for Processing 40 Million Concurrent TCP Connections

C10M is an Internet scalability problem regarding how to handle 10 million simultaneous TCP connections on a web server. Although kernel- and user-level approaches have been proposed to increase TCP stack scalability on multicore systems, C10M is still an open problem. In this paper we present Janus, a high-performance user-level TCP stack that focuses on serving massive TCP connections. In addition to adopting well- known techniques, our design (1) separates packet I/O cores from TCP processing cores to achieve high scalability and flexibility on a multicore system and (2) lets each application run as a per- connection coroutine together with a packet processing loop, which greatly improves cache affinity and saves memory. We demonstrate that Janus can accept 1.86 million new connections per second while maintaining 40 million concurrent connections and significantly outperforms Linux and state-of-the-art user-space network stacks in both throughput and connection concurrency.