  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
