On Wed, Feb 03, 2016@12:50:06AM +0100, Mark Jacobson wrote:

Output is below. I'm aware the distro hints are fairly invalid.

They're all invalid. This kernel must have forked before the affinity
hints were fixed for a blk-mq nvme driver. A more optimal affinity hint
would match the mq's cpu_list, which is how it looks upstream.

I guess your platform strongly prefers CPU 0 when allowed. You can
either manually override the smp_affinity, use an out-of-tree driver
with a fix and let irqbalance handle it.