Hi,

On Friday, October 28, 2016 09:30:07 AM Jens Axboe wrote:

On 10/28/2016 03:32 AM, Linus Walleij wrote:

quoted

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.

Yes, I'm already considering this for rewritten version of my
patch set as it may also help with performance when compared to
non blk-mq case.

Significant amount of time is spent on DMA map/unmap operations
on ARM MMC hosts and I would like to do these DMA (un)mapping-s
in parallel for two (or more) requests to check whether it helps
the performance (hopefully the cache controller doesn't serialize
these operations).

BTW I'm following the discussion and still would like to help with
getting blk-mq work for MMC.  I'm just quite busy with other things
at the moment.

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.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics