So what you say is you saw a consomed == 1 [1] most of the time?

[1] from http://git.infradead.org/nvme.git/commitdiff/eed5a9d925c59e43980047059fde29e3aa0b7836

Exactly. By processing 1 completion per interrupt it makes perfect sense
why this performs poorly, it's not worth paying the soft-irq schedule
for only a single completion.

What I'm curious is how consistent is this with different devices (wish
I had some...)