What You Need to Know About (Smart) Network Interface Cards

Network interface cards (NICs) are fundamental components of modern high-speed networked systems, supporting multi-100 Gbps speeds and increasing programmability. Offloading computation from a server's CPU to a NIC frees a substantial amount of the server's CPU resources, making NICs key to offer competitive cloud services. Therefore, understanding the performance benefits and limitations of offloading a networking application to a NIC is of paramount importance. In this paper, we measure the performance of four different NICs from one of the largest NIC vendors worldwide, supporting 100 Gbps and 200 Gbps. We show that while today's NICs can easily support multi-hundred-gigabit throughputs, performing frequent update operations of a NIC's packet classifier-as network address translators (NATs) and load balancers would do for each incoming connection-results in a dramatic throughput reduction of up to 70 Gbps or complete denial of service. Our conclusion is that all tested NICs cannot support high-speed networking applications that require keeping track of a large number of frequently arriving incoming connections. Furthermore, we show a variety of counter-intuitive performance artefacts including the performance impact of using multiple tables to classify flows of packets.