User Space Network Drivers

The rise of user space packet processing frameworks like DPDK and netmap makes low-level code more accessible to developers and researchers. Previously, driver code was hidden in the kernel and rarely modified-or even looked at-by developers working at higher layers. These barriers are gone nowadays, yet developers still treat user space drivers as black-boxes magically accelerating applications. We want to change this: every researcher building high-speed network applications should understand the intricacies of the underlying drivers, especially if they impact performance. We present ixy, a user space network driver designed for simplicity and educational purposes to show that fast packet IO is not black magic but careful engineering. ixy focuses on the bare essentials of user space packet processing: a packet forwarder including the whole NIC driver uses less than 1,000 lines of C code. This paper is partially written in tutorial style on the case study of our implementations of drivers for both the Intel 82599 family and for virtual VirtIO NICs. The former allows us to reason about driver and framework performance on a stripped-down implementation to assess individual optimizations in isolation. VirtIO support ensures that everyone can run it in a virtual machine. Our code is available as free and open source under the BSD license at https://github.com/emmericp/ixy.