Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler

[Jens Axboe]

On 10/28/2016 03:32 AM, Linus Walleij wrote:
> The patch to enable MQ looks like this:
> https://git.kernel.org/cgit/linux/kernel/git/linusw/linux-stericsson.git/commit/?h=mmc-mq&id=8f79b527e2e854071d8da019451da68d4753f71d

BTW, another viable "hack" for the depth issue would be to expose more
than one hardware queue. It's meant to map to a distinct submission
region in the hardware, but there's nothing stopping the driver from
using it differently. Might not be cleaner than just increasing the
queue depth on a single queue, though.

That still won't solve the issue of lying about it and causing IO
scheduler confusion, of course.

Also, 4.8 and newer have support for BLK_MQ_F_BLOCKING, if you need to
block in ->queue_rq(). That could eliminate the need to offload to a
kthread manually.

--
Jens Axboe