Be interesting to see a version using io_uring, which I think would let you pre-share buffers with the kernel avoiding some copies, and avoid syscall overhead (though the latter seems negligible here).
I'm not claiming it'll be faster! Additionally io_uring has its own set of challenges, such as whether it's better to allocate one ring per core or one ring per application (shared by some or all cores). Pre-sharing buffers has trade-offs too, particularly in application complexity [alignment, you have to be careful not to reuse a buffer before it is consumed] versus the efficiency of zero copy.