Re: [PATCH scsi-misc-2.6 03/05] scsi: make scsi_queue_insert() use blk_requeue_request()

Tejun Heo
2005-04-21T00:20:55Z

Hello, James.

James Bottomley wrote:
> On Wed, 2005-04-20 at 08:15 +0900, Tejun Heo wrote:
>
>>- * Insert this command at the head of the queue for it's device.
>>- * It will go before all other commands that are already in the queue.
>>- *
>>- * NOTE: there is magic here about the way the queue is plugged if
>>- * we have no outstanding commands.
>>- *
>>- * Although this *doesn't* plug the queue, it does call the request
>>- * function. The SCSI request function detects the blocked condition
>>- * and plugs the queue appropriately.
>
>
> This comment still looks appropriate to me ... why do you want to remove
> it?
>

Well, the thing is that we don't really care what exactly happens to
the queue or how the queue is plugged or not. All we need to do are to
requeue the request and kick the queue in the ass. Hmmm, maybe I should
keep the comment about how the request will be put at the head of the
queue, but the second part about plugging doesn't really belong here, I
think.

>
>>+ * Requeue the command.
>> */
>>- blk_insert_request(device->request_queue, cmd->request, 1, cmd, 1);
>>+ spin_lock_irqsave(q->queue_lock, flags);
>>+ blk_requeue_request(q, cmd->request);
>>+ spin_unlock_irqrestore(q->queue_lock, flags);
>>+
>>+ scsi_run_queue(q);
>
>
> Really, wouldn't it be much more efficient simply to call blk_run_queue
> ()? since the blocked flags were set above, that's pretty much what
> scsi_run_queue() collapses to.
>

Yes, that will be more efficient but I don't think it would make any
noticeable difference. IMO, universally using scsi_run_queue() to kick
scsi request queues is better than mixing blk_run_queue() and
scsi_run_queue() for probably unnoticeable optimization. If we start to
mix'em, we need to rationalize why specific one is chosen in specific
places and that's just unnecessary.

Thanks.

--
tejun