On Mon, 2018-10-29 at 14:09 -0600, Jens Axboe wrote:

hctx->type will be set to the value of the first type. This is all driver
private, blk-mq could not care less what the value of the type means.

As to the other question, it works just fine since that is the queue
that is being accessed. There's no confusion there. I think you're
misunderstanding how it's seutp. To use nvme as the example, type 0
would be reads, 1 writes, and 2 pollable queues. If reads and writes
share the same set of hardware queues, then type 1 simply doesn't
exist in terms of ->flags_to_type() return value. This is purely
driven by the driver. That hook is the only decider of where something
will go. If we share hctx sets, we share the same hardware queue as
well. There is just the one set for that case.

How about adding a comment in blk-mq.h that explains that hardware queues can
be shared among different hardware queue types? I think this is nontrivial and
deserves a comment.

Thanks,

Bart.