Io uring and xdp enter 2024

Last year (2023), I spent significant time writing code using XDP and io_uring. The latter was delightful, the former less so. My summary of io_uring through liburing 2.3 hit #1 on HackerNews (twice!) and the great LWN, which pleased me. Work on these technologies has progressed, and it seems time for an update.

XDP

One of the big problems I had with AF_XDP sockets was the lack of support for large packets. One could typically only use an MTU of 3KB and some change, putting XDP at a disadvantage relative to systems which happily process 8KB frames. One must supply XDP_USE_SG, and supply xdp.frags as the program's section name. A single RXring frame might not hold the entire packet, in which case it will be written across several ring frames (with attendant multiple RXring descriptors). The XDP_PKT_CONTD flag is set in the options field if there are more frames. They will always be written in order, and if there are insufficient frames to write all data, none will be written.

io_uring

Easily the most exciting development is integration of futexes (Jens Axboe 2023-07-20 "Add io_uring futex/futexv support").

See also

• AF_XDP kernel documentation