[PATCH v6 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs()

[PATCH v6 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs()

[Suwan Kim]

This patch serise adds support for polling I/O and mq_ops->queue_rqs()
to virtio-blk driver.

Changes

v5 -> v6
    - patch1 : virtblk_poll
        - Remove memset in init_vq()
        - Fix space indent in init_vq()
        - Replace if condition with positive check in virtblk_map_queues()
                if (i == HCTX_TYPE_POLL)
                        blk_mq_map_queues(&set->map[i]);
                else
                        blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
        - Add Reviewed-by tags
    
    - patch2 : virtio_queue_rqs
        - Add Reviewed-by tags

v4 -> v5
    - patch1 : virtblk_poll
        - Replace "req_done" with "found" in virtblk_poll()
        - Split for loop into two distinct for loop in init_vq()
          that sets callback function for each default/poll queues
        - Replace "if (i == HCTX_TYPE_DEFAULT)" with "i != HCTX_TYPE_POLL"
          in virtblk_map_queues()
        - Replace "virtblk_unmap_data(req, vbr);" with
          "virtblk_unmap_data(req, blk_mq_rq_to_pdu(req);"
          in virtblk_complete_batch()
    
    - patch2 : virtio_queue_rqs
        - Instead of using vbr.sg_num field, use vbr->sg_table.nents.
          So, remove sg_num field in struct virtblk_req
        - Drop the unnecessary argument of virtblk_add_req() because it
          doens't need "data_sg" and "have_data". It can be derived from "vbr"
          argument.
        - Add Reviewed-by tag from Stefan

v3 -> v4
    - patch1 : virtblk_poll
        - Add print the number of default/read/poll queues in init_vq()
        - Add blk_mq_start_stopped_hw_queues() to virtblk_poll()
              virtblk_poll()
                  ...
                  if (req_done)
                                   blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
                  ...

    - patch2 : virtio_queue_rqs
        - Modify virtio_queue_rqs() to hold lock only once when it adds
          requests to virtqueue just before virtqueue notify.
          It will guarantee that virtio_queue_rqs() will not use
          previous req again.

v2 -> v3
        - Fix warning by kernel test robot
          
            static int virtblk_poll()
                ...
                if (!blk_mq_add_to_batch(req, iob, virtblk_result(vbr),
                                                   -> vbr->status,

v1 -> v2
        - To receive the number of poll queues from user,
          use module parameter instead of QEMU uapi change.

        - Add the comment about virtblk_map_queues().

        - Add support for mq_ops->queue_rqs() to implement submit side
          batch.

Suwan Kim (2):
  virtio-blk: support polling I/O
  virtio-blk: support mq_ops->queue_rqs()

 drivers/block/virtio_blk.c | 220 +++++++++++++++++++++++++++++++++----
 1 file changed, 201 insertions(+), 19 deletions(-)

-- 
2.26.3

[PATCH v6 1/2] virtio-blk: support polling I/O

[Suwan Kim]

This patch supports polling I/O via virtio-blk driver. Polling
feature is enabled by module parameter "poll_queues" and it sets
dedicated polling queues for virtio-blk. This patch improves the
polling I/O throughput and latency.

The virtio-blk driver doesn't not have a poll function and a poll
queue and it has been operating in interrupt driven method even if
the polling function is called in the upper layer.

virtio-blk polling is implemented upon 'batched completion' of block
layer. virtblk_poll() queues completed request to io_comp_batch->req_list
and later, virtblk_complete_batch() calls unmap function and ends
the requests in batch.

virtio-blk reads the number of poll queues from module parameter
"poll_queues". If VM sets queue parameter as below,
("num-queues=N" [QEMU property], "poll_queues=M" [module parameter])
It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
queues, the poll queues have no callback function.

Regarding HW-SW queue mapping, the default queue mapping uses the
existing method that condsiders MSI irq vector. But the poll queue
doesn't have an irq, so it uses the regular blk-mq cpu mapping.

For verifying the improvement, I did Fio polling I/O performance test
with io_uring engine with the options below.
(io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
queues for VM.

As a result, IOPS and average latency improved about 10%.

Test result:

- Fio io_uring poll without virtio-blk poll support
	-- numjobs=1 : IOPS = 339K, avg latency = 188.33us
	-- numjobs=2 : IOPS = 367K, avg latency = 347.33us
	-- numjobs=4 : IOPS = 383K, avg latency = 682.06us

- Fio io_uring poll with virtio-blk poll support
	-- numjobs=1 : IOPS = 385K, avg latency = 165.94us
	-- numjobs=2 : IOPS = 408K, avg latency = 313.28us
	-- numjobs=4 : IOPS = 424K, avg latency = 613.05us

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
---
 drivers/block/virtio_blk.c | 106 +++++++++++++++++++++++++++++++++++--
 1 file changed, 103 insertions(+), 3 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index a8bcf3f664af..957e15b87651 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
 		 "0 for no limit. "
 		 "Values > nr_cpu_ids truncated to nr_cpu_ids.");
 
+static unsigned int poll_queues;
+module_param(poll_queues, uint, 0644);
+MODULE_PARM_DESC(poll_queues, "The number of dedicated virtqueues for polling I/O");
+
 static int major;
 static DEFINE_IDA(vd_index_ida);
 
@@ -74,6 +78,7 @@ struct virtio_blk {
 
 	/* num of vqs */
 	int num_vqs;
+	int io_queues[HCTX_MAX_TYPES];
 	struct virtio_blk_vq *vqs;
 };
 
@@ -512,6 +517,7 @@ static int init_vq(struct virtio_blk *vblk)
 	const char **names;
 	struct virtqueue **vqs;
 	unsigned short num_vqs;
+	unsigned int num_poll_vqs;
 	struct virtio_device *vdev = vblk->vdev;
 	struct irq_affinity desc = { 0, };
 
@@ -520,6 +526,7 @@ static int init_vq(struct virtio_blk *vblk)
 				   &num_vqs);
 	if (err)
 		num_vqs = 1;
+
 	if (!err && !num_vqs) {
 		dev_err(&vdev->dev, "MQ advertised but zero queues reported\n");
 		return -EINVAL;
@@ -529,6 +536,17 @@ static int init_vq(struct virtio_blk *vblk)
 			min_not_zero(num_request_queues, nr_cpu_ids),
 			num_vqs);
 
+	num_poll_vqs = min_t(unsigned int, poll_queues, num_vqs - 1);
+
+	vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs;
+	vblk->io_queues[HCTX_TYPE_READ] = 0;
+	vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs;
+
+	dev_info(&vdev->dev, "%d/%d/%d default/read/poll queues\n",
+				vblk->io_queues[HCTX_TYPE_DEFAULT],
+				vblk->io_queues[HCTX_TYPE_READ],
+				vblk->io_queues[HCTX_TYPE_POLL]);
+
 	vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
 	if (!vblk->vqs)
 		return -ENOMEM;
@@ -541,12 +559,18 @@ static int init_vq(struct virtio_blk *vblk)
 		goto out;
 	}
 
-	for (i = 0; i < num_vqs; i++) {
+	for (i = 0; i < num_vqs - num_poll_vqs; i++) {
 		callbacks[i] = virtblk_done;
 		snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
 		names[i] = vblk->vqs[i].name;
 	}
 
+	for (; i < num_vqs; i++) {
+		callbacks[i] = NULL;
+		snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
+		names[i] = vblk->vqs[i].name;
+	}
+
 	/* Discover virtqueues and write information to configuration.  */
 	err = virtio_find_vqs(vdev, num_vqs, vqs, callbacks, names, &desc);
 	if (err)
@@ -692,16 +716,89 @@ static const struct attribute_group *virtblk_attr_groups[] = {
 static int virtblk_map_queues(struct blk_mq_tag_set *set)
 {
 	struct virtio_blk *vblk = set->driver_data;
+	int i, qoff;
+
+	for (i = 0, qoff = 0; i < set->nr_maps; i++) {
+		struct blk_mq_queue_map *map = &set->map[i];
+
+		map->nr_queues = vblk->io_queues[i];
+		map->queue_offset = qoff;
+		qoff += map->nr_queues;
+
+		if (map->nr_queues == 0)
+			continue;
+
+		/*
+		 * Regular queues have interrupts and hence CPU affinity is
+		 * defined by the core virtio code, but polling queues have
+		 * no interrupts so we let the block layer assign CPU affinity.
+		 */
+		if (i == HCTX_TYPE_POLL)
+			blk_mq_map_queues(&set->map[i]);
+		else
+			blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
+	}
+
+	return 0;
+}
+
+static void virtblk_complete_batch(struct io_comp_batch *iob)
+{
+	struct request *req;
 
-	return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
-					vblk->vdev, 0);
+	rq_list_for_each(&iob->req_list, req) {
+		virtblk_unmap_data(req, blk_mq_rq_to_pdu(req));
+		virtblk_cleanup_cmd(req);
+	}
+	blk_mq_end_request_batch(iob);
+}
+
+static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
+{
+	struct virtio_blk *vblk = hctx->queue->queuedata;
+	struct virtio_blk_vq *vq = hctx->driver_data;
+	struct virtblk_req *vbr;
+	unsigned long flags;
+	unsigned int len;
+	int found = 0;
+
+	spin_lock_irqsave(&vq->lock, flags);
+
+	while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
+		struct request *req = blk_mq_rq_from_pdu(vbr);
+
+		found++;
+		if (!blk_mq_add_to_batch(req, iob, vbr->status,
+						virtblk_complete_batch))
+			blk_mq_complete_request(req);
+	}
+
+	if (found)
+		blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
+
+	spin_unlock_irqrestore(&vq->lock, flags);
+
+	return found;
+}
+
+static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
+			  unsigned int hctx_idx)
+{
+	struct virtio_blk *vblk = data;
+	struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
+
+	WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags);
+	hctx->driver_data = vq;
+	return 0;
 }
 
 static const struct blk_mq_ops virtio_mq_ops = {
 	.queue_rq	= virtio_queue_rq,
 	.commit_rqs	= virtio_commit_rqs,
+	.init_hctx	= virtblk_init_hctx,
 	.complete	= virtblk_request_done,
 	.map_queues	= virtblk_map_queues,
+	.poll		= virtblk_poll,
 };
 
 static unsigned int virtblk_queue_depth;
@@ -778,6 +875,9 @@ static int virtblk_probe(struct virtio_device *vdev)
 		sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
 	vblk->tag_set.driver_data = vblk;
 	vblk->tag_set.nr_hw_queues = vblk->num_vqs;
+	vblk->tag_set.nr_maps = 1;
+	if (vblk->io_queues[HCTX_TYPE_POLL])
+		vblk->tag_set.nr_maps = 3;
 
 	err = blk_mq_alloc_tag_set(&vblk->tag_set);
 	if (err)
-- 
2.26.3

[PATCH v6 2/2] virtio-blk: support mq_ops->queue_rqs()

[Suwan Kim]

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>
---
 drivers/block/virtio_blk.c | 114 +++++++++++++++++++++++++++++++------
 1 file changed, 98 insertions(+), 16 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 957e15b87651..924a1cd6cdca 100644
--- 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,
-- 
2.26.3

Re: [PATCH v6 1/2] virtio-blk: support polling I/O

[Chaitanya Kulkarni]

On 4/6/22 08:32, Suwan Kim wrote:
> This patch supports polling I/O via virtio-blk driver. Polling
> feature is enabled by module parameter "poll_queues" and it sets
> dedicated polling queues for virtio-blk. This patch improves the
> polling I/O throughput and latency.
> 
> The virtio-blk driver doesn't not have a poll function and a poll
> queue and it has been operating in interrupt driven method even if
> the polling function is called in the upper layer.
> 
> virtio-blk polling is implemented upon 'batched completion' of block
> layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> and later, virtblk_complete_batch() calls unmap function and ends
> the requests in batch.
> 
> virtio-blk reads the number of poll queues from module parameter
> "poll_queues". If VM sets queue parameter as below,
> ("num-queues=N" [QEMU property], "poll_queues=M" [module parameter])
> It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> queues, the poll queues have no callback function.
> 
> Regarding HW-SW queue mapping, the default queue mapping uses the
> existing method that condsiders MSI irq vector. But the poll queue
> doesn't have an irq, so it uses the regular blk-mq cpu mapping.
> 
> For verifying the improvement, I did Fio polling I/O performance test
> with io_uring engine with the options below.
> (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> queues for VM.
> 
> As a result, IOPS and average latency improved about 10%.
> 
> Test result:
> 
> - Fio io_uring poll without virtio-blk poll support
> 	-- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> 	-- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> 	-- numjobs=4 : IOPS = 383K, avg latency = 682.06us
> 
> - Fio io_uring poll with virtio-blk poll support
> 	-- numjobs=1 : IOPS = 385K, avg latency = 165.94us
> 	-- numjobs=2 : IOPS = 408K, avg latency = 313.28us
> 	-- numjobs=4 : IOPS = 424K, avg latency = 613.05us
> 
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
>

Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

-ck

Re: [PATCH v6 2/2] virtio-blk: support mq_ops->queue_rqs()

[Chaitanya Kulkarni]

On 4/6/22 08:32, Suwan Kim wrote:
> 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>
> ---


Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

-ck

Re: [PATCH v6 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs()

[Chaitanya Kulkarni]

On 4/6/22 08:32, Suwan Kim wrote:
> This patch serise adds support for polling I/O and mq_ops->queue_rqs()
> to virtio-blk driver.
> 

Thanks for doing this work, can you please add a blktests [1]
for this so it will get tested by different ppl under different
environment by various backend for each release ?

Please CC me and Omar for blktests I'll be happy to review.

-ck

[1] https://github.com/osandov/blktests.git

Re: [PATCH v6 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs()

[Suwan Kim]

On Thu, Apr 07, 2022 at 07:36:00PM +0000, Chaitanya Kulkarni wrote:
> On 4/6/22 08:32, Suwan Kim wrote:
> > This patch serise adds support for polling I/O and mq_ops->queue_rqs()
> > to virtio-blk driver.
> > 
> 
> Thanks for doing this work, can you please add a blktests [1]
> for this so it will get tested by different ppl under different
> environment by various backend for each release ?
> 
> Please CC me and Omar for blktests I'll be happy to review.
> 
> -ck
> 
> [1] https://github.com/osandov/blktests.git
> 
> 

Hi Chaitanya,

Sure. I will do.
Do I need to add a new test script about vdN device IO polling
to blktests/tests/block/?

Regards,
Suwan Kim

Re: [PATCH v6 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs()

[Chaitanya Kulkarni]

> 
> Hi Chaitanya,
> 
> Sure. I will do.
> Do I need to add a new test script about vdN device IO polling
> to blktests/tests/block/?
> 

That will create confusion as block category testcases are different 
than virtio-blk. So you need to create a new category virtio-blk and
add testcases to that one.

-ck


> Regards,
> Suwan Kim
> 

Re: [PATCH v6 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs()

[Suwan Kim]

On Thu, Apr 07, 2022 at 12:32:05AM +0900, Suwan Kim wrote:
> This patch serise adds support for polling I/O and mq_ops->queue_rqs()
> to virtio-blk driver.
> 
> Changes
> 
> v5 -> v6
>     - patch1 : virtblk_poll
>         - Remove memset in init_vq()
>         - Fix space indent in init_vq()
>         - Replace if condition with positive check in virtblk_map_queues()
>                 if (i == HCTX_TYPE_POLL)
>                         blk_mq_map_queues(&set->map[i]);
>                 else
>                         blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
>         - Add Reviewed-by tags
>     
>     - patch2 : virtio_queue_rqs
>         - Add Reviewed-by tags
> 
> v4 -> v5
>     - patch1 : virtblk_poll
>         - Replace "req_done" with "found" in virtblk_poll()
>         - Split for loop into two distinct for loop in init_vq()
>           that sets callback function for each default/poll queues
>         - Replace "if (i == HCTX_TYPE_DEFAULT)" with "i != HCTX_TYPE_POLL"
>           in virtblk_map_queues()
>         - Replace "virtblk_unmap_data(req, vbr);" with
>           "virtblk_unmap_data(req, blk_mq_rq_to_pdu(req);"
>           in virtblk_complete_batch()
>     
>     - patch2 : virtio_queue_rqs
>         - Instead of using vbr.sg_num field, use vbr->sg_table.nents.
>           So, remove sg_num field in struct virtblk_req
>         - Drop the unnecessary argument of virtblk_add_req() because it
>           doens't need "data_sg" and "have_data". It can be derived from "vbr"
>           argument.
>         - Add Reviewed-by tag from Stefan
> 
> v3 -> v4
>     - patch1 : virtblk_poll
>         - Add print the number of default/read/poll queues in init_vq()
>         - Add blk_mq_start_stopped_hw_queues() to virtblk_poll()
>               virtblk_poll()
>                   ...
>                   if (req_done)
>                                    blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
>                   ...
> 
>     - patch2 : virtio_queue_rqs
>         - Modify virtio_queue_rqs() to hold lock only once when it adds
>           requests to virtqueue just before virtqueue notify.
>           It will guarantee that virtio_queue_rqs() will not use
>           previous req again.
> 
> v2 -> v3
>         - Fix warning by kernel test robot
>           
>             static int virtblk_poll()
>                 ...
>                 if (!blk_mq_add_to_batch(req, iob, virtblk_result(vbr),
>                                                    -> vbr->status,
> 
> v1 -> v2
>         - To receive the number of poll queues from user,
>           use module parameter instead of QEMU uapi change.
> 
>         - Add the comment about virtblk_map_queues().
> 
>         - Add support for mq_ops->queue_rqs() to implement submit side
>           batch.
> 
> Suwan Kim (2):
>   virtio-blk: support polling I/O
>   virtio-blk: support mq_ops->queue_rqs()
> 
>  drivers/block/virtio_blk.c | 220 +++++++++++++++++++++++++++++++++----
>  1 file changed, 201 insertions(+), 19 deletions(-)
> 
> -- 
> 2.26.3

Hi Michael,

Can these patches be merged to your branch?

Regards,
Suwan Kim