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

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Date:	Tue, 19 Jun 2012 10:30:00 +0800
From:	Asias He <asias@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Christoph Hellwig <hch@....de>,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk

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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