One of the comments to the article is really interesting. The recent Meltdown stuff has really blown up the cost of privilege transitions, because now people expect non-architectural data not to leak across privilege boundaries. System calls are about twice as slow as they used to be. Meanwhile, I/O is faster than ever, with PCIE and NVME. Io_uring offers the opportunity to avoid privilege transitions through asynchronous calls based on writing to a memory buffer shared between user space and the kernel. That has the potential for fundamentally changing the basis system call interface. As the article hints at, the trick is designing the API so you can construct as large a block of work to be done asynchronously as possible. At the limit, you could really push down the core of your I/O loop into the kernel, hence the suggestions that BPF programs could be submitted through the ring to chain operations all within the kernel.

(Incidentally, this is a good illustration of the flexibility of UNIX’s model of describing everything with a file descriptor. The same interface meant for asynchronous file I/O was easily extended to network I/O.)