Doesn’t the Linux kernel automatically merge requests for contiguous regions into a single request? I’m not sure 16 read I/Os submitted to io_uring for a contiguous 64kib region will behave differently at the disk level than a single 64kib request. There’s a little bit extra work the kernel has to do to merge the requests but that should be negligible.

In a poorly written micro benchmark test it’s possible the kernel will fail to coalesce all of them because your submissions aren’t visible all at once (ie it starts submitting requests and doesn’t have an opportunity to merge). Whether that actually is possible to happen requires digging a bit more into the Linux kernel source.

Yes that is correct.

You can look at 'rrqm/s' and '%rrqm' in `iostat -x` to get statistics for how many requests are merged, and `rareq-sz` for the average request size.