Re: [PATCH] ublk_drv: don't forward io commands in reserve order

[Ziyang Zhang <ZiyangZhang@linux.alibaba.com>]

On 2022/11/21 23:56, Ming Lei wrote:
> Either ublk_can_use_task_work() is true or not, io commands are
> forwarded to ublk server in reverse order, since llist_add() is
> always to add one element to the head of the list.
> 
> Even though block layer doesn't guarantee request dispatch order,
> requests should be sent to hardware in the sequence order generated
> from io scheduler, which usually considers the request's LBA, and
> order is often important for HDD.
> 
> So forward io commands in the sequence made from io scheduler by
> aligning task work with current io_uring command's batch handling,
> and it has been observed that both can get similar performance data
> if IORING_SETUP_COOP_TASKRUN is set from ublk server.
> 
> Reported-by: Andreas Hindborg <andreas.hindborg@wdc.com>
> Cc: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>

I have tested this with dd. Looks like we get the correct order:

ublk_queue_rq: qid 0 tag 2 sect 12288
__ublk_rq_task_work: complete: op 33, qid 0 tag 2 io_flags 1 addr 7ff16699e000 sect 12288
ublk_queue_rq: qid 0 tag 5 sect 13312
__ublk_rq_task_work: complete: op 33, qid 0 tag 5 io_flags 1 addr 7ff166818000 sect 13312
ublk_queue_rq: qid 0 tag 4 sect 14336
__ublk_rq_task_work: complete: op 33, qid 0 tag 4 io_flags 1 addr 7ff16689a000 sect 14336
ublk_queue_rq: qid 0 tag 6 sect 15360
__ublk_rq_task_work: complete: op 33, qid 0 tag 6 io_flags 1 addr 7ff166796000 sect 15360


Reviewed-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>

Regards,
Zhang