Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk

[Asias He]

On 06/18/2012 06:21 PM, Michael S. Tsirkin wrote:
> On Mon, Jun 18, 2012 at 02:53:10PM +0800, Asias He wrote:
> > +static void virtblk_make_request(struct request_queue *q, struct bio *bio)
> > +{
> > +	struct virtio_blk *vblk = q->queuedata;
> > +	unsigned int num, out = 0, in = 0;
> > +	struct virtblk_req *vbr;
> > +
> > +	BUG_ON(bio->bi_phys_segments + 2 > vblk->sg_elems);
> > +	BUG_ON(bio->bi_rw & (REQ_FLUSH | REQ_FUA));
> > +
> > +	vbr = virtblk_alloc_req(vblk, GFP_NOIO);
> > +	if (!vbr) {
> > +		bio_endio(bio, -ENOMEM);
> > +		return;
> > +	}
> > +
> > +	vbr->bio = bio;
> > +	vbr->req = NULL;
> > +	vbr->out_hdr.type = 0;
> > +	vbr->out_hdr.sector = bio->bi_sector;
> > +	vbr->out_hdr.ioprio = bio_prio(bio);
> > +
> > +	sg_set_buf(&vbr->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr));
> > +
> > +	num = blk_bio_map_sg(q, bio, vbr->sg + out);
> > +
> > +	sg_set_buf(&vbr->sg[num + out + in++], &vbr->status,
> > +		   sizeof(vbr->status));
> > +
> > +	if (num) {
> > +		if (bio->bi_rw & REQ_WRITE) {
> > +			vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;
> > +			out += num;
> > +		} else {
> > +			vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
> > +			in += num;
> > +		}
> > +	}
> > +
> > +	spin_lock_irq(vblk->disk->queue->queue_lock);
> > +	if (virtqueue_add_buf(vblk->vq, vbr->sg, out, in, vbr,
> > +			      GFP_ATOMIC) < 0) {
> > +		spin_unlock_irq(vblk->disk->queue->queue_lock);
>
> Any implications of dropping lock like that?
> E.g. for suspend. like we are still discussing with
> unlocked kick?
>
> > +		virtblk_add_buf_wait(vblk, vbr, out, in);
> > +	} else {
> > +		virtqueue_kick(vblk->vq);
>
> Why special case the first call? task state manipulation so expensive?

Hmm. Will switch them.

> > +		spin_unlock_irq(vblk->disk->queue->queue_lock);
> > +	}
> > +}
> > +
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--
Asias


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