Commit 0e9911fa authored by Suwan Kim's avatar Suwan Kim Committed by Michael S. Tsirkin
Browse files

virtio-blk: support mq_ops->queue_rqs() 



This patch supports mq_ops->queue_rqs() hook. It has an advantage of
batch submission to virtio-blk driver. It also helps polling I/O because
polling uses batched completion of block layer. Batch submission in
queue_rqs() can boost polling performance.

In queue_rqs(), it iterates plug->mq_list, collects requests that
belong to same HW queue until it encounters a request from other
HW queue or sees the end of the list.
Then, virtio-blk adds requests into virtqueue and kicks virtqueue
to submit requests.

If there is an error, it inserts error request to requeue_list and
passes it to ordinary block layer path.

For verification, I did fio test.
(io_uring, randread, direct=1, bs=4K, iodepth=64 numjobs=N)
I set 4 vcpu and 2 virtio-blk queues for VM and run fio test 5 times.
It shows about 2% improvement.

                                 |   numjobs=2   |   numjobs=4
      -----------------------------------------------------------
        fio without queue_rqs()  |   291K IOPS   |   238K IOPS
      -----------------------------------------------------------
        fio with queue_rqs()     |   295K IOPS   |   243K IOPS

For polling I/O performance, I also did fio test as below.
(io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=4)
I set 4 vcpu and 2 poll queues for VM.
It shows about 2% improvement in polling I/O.

                                      |   IOPS   |  avg latency
      -----------------------------------------------------------
        fio poll without queue_rqs()  |   424K   |   613.05 usec
      -----------------------------------------------------------
        fio poll with queue_rqs()     |   435K   |   601.01 usec

Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarSuwan Kim <suwan.kim027@gmail.com>
Message-Id: <20220406153207.163134-3-suwan.kim027@gmail.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: default avatarChaitanya Kulkarni <kch@nvidia.com>
parent 4e040052

drivers/block/virtio_blk.c

+98 −16
Original line number Diff line number Diff line
@@ -101,8 +101,7 @@ static inline blk_status_t virtblk_result(struct virtblk_req *vbr) 
	}

}



static int virtblk_add_req(struct virtqueue *vq, struct virtblk_req *vbr,

		struct scatterlist *data_sg, bool have_data)

static int virtblk_add_req(struct virtqueue *vq, struct virtblk_req *vbr)

{

	struct scatterlist hdr, status, *sgs[3];

	unsigned int num_out = 0, num_in = 0;
@@ -110,11 +109,11 @@ static int virtblk_add_req(struct virtqueue *vq, struct virtblk_req *vbr, 
	sg_init_one(&hdr, &vbr->out_hdr, sizeof(vbr->out_hdr));

	sgs[num_out++] = &hdr;



	if (have_data) {

	if (vbr->sg_table.nents) {

		if (vbr->out_hdr.type & cpu_to_virtio32(vq->vdev, VIRTIO_BLK_T_OUT))

			sgs[num_out++] = data_sg;

			sgs[num_out++] = vbr->sg_table.sgl;

		else

			sgs[num_out + num_in++] = data_sg;

			sgs[num_out + num_in++] = vbr->sg_table.sgl;

	}



	sg_init_one(&status, &vbr->status, sizeof(vbr->status));
@@ -304,6 +303,28 @@ static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx) 
		virtqueue_notify(vq->vq);

}



static blk_status_t virtblk_prep_rq(struct blk_mq_hw_ctx *hctx,

					struct virtio_blk *vblk,

					struct request *req,

					struct virtblk_req *vbr)

{

	blk_status_t status;



	status = virtblk_setup_cmd(vblk->vdev, req, vbr);

	if (unlikely(status))

		return status;



	blk_mq_start_request(req);



	vbr->sg_table.nents = virtblk_map_data(hctx, req, vbr);

	if (unlikely(vbr->sg_table.nents < 0)) {

		virtblk_cleanup_cmd(req);

		return BLK_STS_RESOURCE;

	}



	return BLK_STS_OK;

}



static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,

			   const struct blk_mq_queue_data *bd)

{
@@ -311,26 +332,17 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, 
	struct request *req = bd->rq;

	struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);

	unsigned long flags;

	int num;

	int qid = hctx->queue_num;

	bool notify = false;

	blk_status_t status;

	int err;



	status = virtblk_setup_cmd(vblk->vdev, req, vbr);

	status = virtblk_prep_rq(hctx, vblk, req, vbr);

	if (unlikely(status))

		return status;



	blk_mq_start_request(req);



	num = virtblk_map_data(hctx, req, vbr);

	if (unlikely(num < 0)) {

		virtblk_cleanup_cmd(req);

		return BLK_STS_RESOURCE;

	}



	spin_lock_irqsave(&vblk->vqs[qid].lock, flags);

	err = virtblk_add_req(vblk->vqs[qid].vq, vbr, vbr->sg_table.sgl, num);

	err = virtblk_add_req(vblk->vqs[qid].vq, vbr);

	if (err) {

		virtqueue_kick(vblk->vqs[qid].vq);

		/* Don't stop the queue if -ENOMEM: we may have failed to
@@ -360,6 +372,75 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, 
	return BLK_STS_OK;

}



static bool virtblk_prep_rq_batch(struct request *req)

{

	struct virtio_blk *vblk = req->mq_hctx->queue->queuedata;

	struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);



	req->mq_hctx->tags->rqs[req->tag] = req;



	return virtblk_prep_rq(req->mq_hctx, vblk, req, vbr) == BLK_STS_OK;

}



static bool virtblk_add_req_batch(struct virtio_blk_vq *vq,

					struct request **rqlist,

					struct request **requeue_list)

{

	unsigned long flags;

	int err;

	bool kick;



	spin_lock_irqsave(&vq->lock, flags);



	while (!rq_list_empty(*rqlist)) {

		struct request *req = rq_list_pop(rqlist);

		struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);



		err = virtblk_add_req(vq->vq, vbr);

		if (err) {

			virtblk_unmap_data(req, vbr);

			virtblk_cleanup_cmd(req);

			rq_list_add(requeue_list, req);

		}

	}



	kick = virtqueue_kick_prepare(vq->vq);

	spin_unlock_irqrestore(&vq->lock, flags);



	return kick;

}



static void virtio_queue_rqs(struct request **rqlist)

{

	struct request *req, *next, *prev = NULL;

	struct request *requeue_list = NULL;



	rq_list_for_each_safe(rqlist, req, next) {

		struct virtio_blk_vq *vq = req->mq_hctx->driver_data;

		bool kick;



		if (!virtblk_prep_rq_batch(req)) {

			rq_list_move(rqlist, &requeue_list, req, prev);

			req = prev;

			if (!req)

				continue;

		}



		if (!next || req->mq_hctx != next->mq_hctx) {

			req->rq_next = NULL;

			kick = virtblk_add_req_batch(vq, rqlist, &requeue_list);

			if (kick)

				virtqueue_notify(vq->vq);



			*rqlist = next;

			prev = NULL;

		} else

			prev = req;

	}



	*rqlist = requeue_list;

}



/* return id (s/n) string for *disk to *id_str

 */

static int virtblk_get_id(struct gendisk *disk, char *id_str)
@@ -794,6 +875,7 @@ static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data, 


static const struct blk_mq_ops virtio_mq_ops = {

	.queue_rq	= virtio_queue_rq,

	.queue_rqs	= virtio_queue_rqs,

	.commit_rqs	= virtio_commit_rqs,

	.init_hctx	= virtblk_init_hctx,

	.complete	= virtblk_request_done,