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

[Nick Piggin]

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);


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