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: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
Message-Id: <20220406153207.163134-3-suwan.kim027@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

drivers/block/virtio_blk.c

@@ -101,20 +101,19 @@ 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;
 
  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));
@@ -304,33 +303,46 @@ 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)
 {
  struct virtio_blk *vblk = hctx->queue->queuedata;
  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,