On Fri, Dec 03, 2021 at 02:45:44PM -0700, Jens Axboe wrote:

This enables the block layer to send us a full plug list of requests
that need submitting. The block layer guarantees that they all belong
to the same queue, but we do have to check the hardware queue mapping
for each request.

If errors are encountered, leave them in the passed in list. Then the
block layer will handle them individually.

This is good for about a 4% improvement in peak performance, taking us
from 9.6M to 10M IOPS/core.

This looks pretty similar to my proposed cleanups (which is nice), but
back then you mentioned the cleaner version was much slower.  Do you
know what brought the speed back in this version?