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>

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index ad5f9ce8f3f9cf6fbbc93e1c0be4244a18c90898..6fc7850c2b0a0cb0c6bcdd2392fbeef363d47350 100644 (file)
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -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,