As Shockneck said, CIO/DIO is said to be better for random reads/write afaik.
You could check with vmstat -v if there are still any blocked buffers counting up and tune them with the appropriate ioo parameters.
Also you can check about aio, if there is any usage of it or something close to it's limits with "iostat -A" and also the shift+a option in nmon, to see how many aioservers are being used currently.
Edit:
Ah I see we had a foregoing discussion already here
https://www.unix.com/unix-advanced-ex...evice-cio.html
Are you sure you need cio? You hadn't shown the "vmstat -v" back then still.
There is also the possibility to change attributes for FC adapter (like lg_term_dma, max_xfer_size and num_cmd_elems) and disks (like queue_depth or max_coalesce) with chdev and reading them out with lsattr. But before doing that, I would start to sort things out with AIO if appropriate and vmstat -v/iostat.