alt Hacker NewsNot speaking of ls which is more about metadata operations, but general file read/write workloads:
io_uring requires API changes because you don't call it like the old read(please_fill_this_buffer). You maintain a pool of buffer that belong to the ringbuffer, and reads take buffers from the pool. You consume the data from the buffer and return it to the pool.
With the older style, you're required to maintain O(pending_reads) buffers. With the io_uring style, you have a pool of O(num_reads_completing_at_once) (I assume with backpressure but haven't actually checked).
In a single threaded flow your buffer pool is just the buffer you were given, and you don't return until the call completes. There are no actual concurrent calls in the ring. All you're doing is using io_uring to avoid syscall.
Other replies lead me to believe it's not worth doing though, that it would not actually save syscalls and might make things worse.