Re: [PATCH] blk-mq: run the hw queue synchronously for unplugged scheduler inserts

[Qiliang Yuan]

Hi Jens, Ming,

Gentle ping on this one. It fixes a v7.2 regression from 9cbbac29d752
("block: Remove redundant plug in __submit_bio()"): unplugged I/O to a
device with an I/O scheduler is now run from kblockd, and the kworker
preempts the submitter once per I/O. A single-queue null_blk device with
mq-deadline drops from 289K to 193K IOPS, and a single-queue ublk device
from 265K to 113K.

Every single-queue device that defaults to mq-deadline is affected, so it
would be good to get this fixed in 7.3. Any comments are welcome.

Thanks,
Qiliang