Scaling Software-Defined Network Controllers on Multicore Servers

Software defined networks (SDN) introduce centralized controllers to drastically increase network programmability. The simplicity of a logical centralized controller, however, can come at the cost of controller programming complexity and scalability. In this paper, we present McNettle, an extensible SDN controller system whose control event processing throughput scales with the number of system CPU cores and which supports control algorithms requiring globally visible state changes occurring at flow arrival rates. Programmers extend McNettle by writing event handlers and background programs in a high-level functional programming language extended with shared state and memory transactions. We implement our framework in Haskell and leverage the multicore facilities of the Glasgow Haskell Compiler (GHC) and runtime system. Our implementation schedules event handlers, allocates memory, optimizes message parsing and serialization, and buffers system calls in order to optimize cache usage, OS processing, and runtime system overhead. We identify and fix bottlenecks in the GHC runtime system and IO manager. Our experiments show that McNettle can serve up to 5000 switches using a single controller with 46 cores, achieving throughput of over 14 million flows per second, near-linear scaling up to 46 cores, and latency under 10 ms with loads consisting of up to 1500 switches.