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

[Ming Lei <tom.leiming@gmail.com>]

On Sat, Oct 10, 2026 at 10:35:47AM +0800, Qiliang Yuan wrote:
> 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

It is hard to say it is one regression cause 9cbbac29d752 is doing correct
thing, and single request isn't supposed to dispatch via plug list, and it
only recovers to previous behavior before 060406c61c7c 
("block: add plug while submitting IO").

> 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.

For both SQ null & ublk, you can switch to none for better performance.

> 
> 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.

Not sure you can observe big difference for other real SQ device.


Thanks,
Ming