Re: [patch] use cheaper elv_queue_empty when unplug a device

[Nick Piggin <nickpiggin@yahoo.com.au>]

Jens Axboe wrote:
> On Tue, Mar 29 2005, Nick Piggin wrote:
> 
>>@@ -2577,19 +2577,18 @@ static int __make_request(request_queue_
>> 	spin_lock_prefetch(q->queue_lock);
>> 
>> 	barrier = bio_barrier(bio);
>>-	if (barrier && (q->ordered == QUEUE_ORDERED_NONE)) {
>>+	if (unlikely(barrier) && (q->ordered == QUEUE_ORDERED_NONE)) {
>> 		err = -EOPNOTSUPP;
>> 		goto end_io;
>> 	}
>> 
>>-again:
>> 	spin_lock_irq(q->queue_lock);
>> 
>> 	if (elv_queue_empty(q)) {
>> 		blk_plug_device(q);
>> 		goto get_rq;
>> 	}
> 
> 
> This should just goto get_rq, the plug should happen only at the end
> where you did add it:
> 

Yes I see. I'll fix that up.

> 
>>@@ -2693,10 +2675,11 @@ get_rq:
>> 	req->rq_disk = bio->bi_bdev->bd_disk;
>> 	req->start_time = jiffies;
>> 
>>+	spin_lock_irq(q->queue_lock);
>>+	if (elv_queue_empty(q))
>>+		blk_plug_device(q);
>> 	add_request(q, req);
>> out:
>>-	if (freereq)
>>-		__blk_put_request(q, freereq);
>> 	if (bio_sync(bio))
>> 		__generic_unplug_device(q);
>> 
> 
>