Re: [PATCH] ublk: eliminate unnecessary io_cmds queue

[Uday Shankar <ushankar@purestorage.com>]

On Thu, Oct 10, 2024 at 11:45:03AM +0800, Ming Lei wrote:
> >  static void ublk_queue_cmd(struct ublk_queue *ubq, struct request *rq)
> >  {
> > -	struct ublk_rq_data *data = blk_mq_rq_to_pdu(rq);
> > -
> > -	if (llist_add(&data->node, &ubq->io_cmds)) {
> > -		struct ublk_io *io = &ubq->ios[rq->tag];
> > +	struct ublk_io *io = &ubq->ios[rq->tag];
> >  
> > -		io_uring_cmd_complete_in_task(io->cmd, ublk_rq_task_work_cb);
> > -	}
> > +	ublk_get_uring_cmd_pdu(io->cmd)->req = rq;
> > +	io_uring_cmd_complete_in_task(io->cmd, __ublk_rq_task_work);
> >  }
> 
> I'd suggest to comment that io_uring_cmd_complete_in_task() needs to
> maintain io command order.

Sorry, can you explain why this is important? Generally speaking
out-of-order completion of I/Os is considered okay, so what's the issue
if the dispatch to the ublk server here is not in order?