Rearchitecting the TCP Stack for I/O-Offloaded Content Delivery.

The recent advancement of high-bandwidth I/O devices enables scalable delivery of online content. Unfortunately, the traditional programming model for content servers has a tight dependency on the CPU, which severely limits the overall performance. Our experiments reveal that over 70% of CPU cycles are spent on simple tasks such as disk and network I/O operations in online content delivery. In this work, we present IO-TCP, a split TCP stack design that drastically reduces the burden on CPU for online content delivery. IO-TCP offloads disk I/O and TCP packet transfer to SmartNIC while the rest of the operations are executed on the CPU side. This division of labor realizes the separation of control and data planes of a TCP stack where the CPU side assumes the full control of the stack operation while only the data plane operations are offloaded to SmartNIC for high performance. Our evaluation shows that IO-TCP-ported lighttpd with a single CPU core outperforms the Atlas server and lighttpd on Linux TCP for TLS file transfer by 1.8x and 2.1x, respectively, even if they use all 10 CPU cores.