[PATCH v4 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs()

[PATCH v4 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

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 | 222 ++++++++++++++++++++++++++++++++++---
 1 file changed, 207 insertions(+), 15 deletions(-)

-- 
2.26.3

[PATCH v4 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 "num_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
"num_poll_queues". If VM sets queue parameter as below,
("num-queues=N" [QEMU property], "num_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

Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
---
 drivers/block/virtio_blk.c | 112 +++++++++++++++++++++++++++++++++++--
 1 file changed, 108 insertions(+), 4 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 8c415be86732..c2d955da0006 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 num_poll_queues;
+module_param(num_poll_queues, uint, 0644);
+MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
+
 static int major;
 static DEFINE_IDA(vd_index_ida);
 
@@ -81,6 +85,7 @@ struct virtio_blk {
 
 	/* num of vqs */
 	int num_vqs;
+	int io_queues[HCTX_MAX_TYPES];
 	struct virtio_blk_vq *vqs;
 };
 
@@ -548,6 +553,7 @@ 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, };
 
@@ -556,6 +562,7 @@ 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;
@@ -565,6 +572,18 @@ 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, num_poll_queues, num_vqs - 1);
+
+	memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES);
+	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;
@@ -578,8 +597,13 @@ static int init_vq(struct virtio_blk *vblk)
 	}
 
 	for (i = 0; i < num_vqs; i++) {
-		callbacks[i] = virtblk_done;
-		snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
+		if (i < num_vqs - num_poll_vqs) {
+			callbacks[i] = virtblk_done;
+			snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
+		} else {
+			callbacks[i] = NULL;
+			snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
+		}
 		names[i] = vblk->vqs[i].name;
 	}
 
@@ -728,16 +752,93 @@ 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_DEFAULT)
+			blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
+		else
+			blk_mq_map_queues(&set->map[i]);
+	}
+
+	return 0;
+}
+
+static void virtblk_complete_batch(struct io_comp_batch *iob)
+{
+	struct request *req;
+	struct virtblk_req *vbr;
+
+	rq_list_for_each(&iob->req_list, req) {
+		vbr = blk_mq_rq_to_pdu(req);
+		virtblk_unmap_data(req, vbr);
+		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;
+	bool req_done = false;
+	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);
 
-	return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
-					vblk->vdev, 0);
+		found++;
+		if (!blk_mq_add_to_batch(req, iob, vbr->status,
+						virtblk_complete_batch))
+			blk_mq_complete_request(req);
+		req_done = true;
+	}
+
+	if (req_done)
+		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;
@@ -816,6 +917,9 @@ 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 v4 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

Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
---
 drivers/block/virtio_blk.c | 110 +++++++++++++++++++++++++++++++++----
 1 file changed, 99 insertions(+), 11 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index c2d955da0006..03e4455c23e3 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -92,6 +92,7 @@ struct virtio_blk {
 struct virtblk_req {
 	struct virtio_blk_outhdr out_hdr;
 	u8 status;
+	int sg_num;
 	struct sg_table sg_table;
 	struct scatterlist sg[];
 };
@@ -311,18 +312,13 @@ static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx)
 		virtqueue_notify(vq->vq);
 }
 
-static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
-			   const struct blk_mq_queue_data *bd)
+static blk_status_t virtblk_prep_rq(struct blk_mq_hw_ctx *hctx,
+					struct virtio_blk *vblk,
+					struct request *req,
+					struct virtblk_req *vbr)
 {
-	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;
+	int num;
 
 	status = virtblk_setup_cmd(vblk->vdev, req, vbr);
 	if (unlikely(status))
@@ -335,9 +331,30 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
 		virtblk_cleanup_cmd(req);
 		return BLK_STS_RESOURCE;
 	}
+	vbr->sg_num = num;
+
+	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 qid = hctx->queue_num;
+	bool notify = false;
+	blk_status_t status;
+	int err;
+
+	status = virtblk_prep_rq(hctx, vblk, req, vbr);
+	if (unlikely(status))
+		return status;
 
 	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,
+				vbr->sg_table.sgl, vbr->sg_num);
 	if (err) {
 		virtqueue_kick(vblk->vqs[qid].vq);
 		/* Don't stop the queue if -ENOMEM: we may have failed to
@@ -367,6 +384,76 @@ 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,
+					vbr->sg_table.sgl, vbr->sg_num);
+		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)
@@ -834,6 +921,7 @@ 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 v4 1/2] virtio-blk: support polling I/O

[Suwan Kim]

On Mon, Apr 04, 2022 at 06:28:04PM +0900, Suwan Kim wrote:
> This patch supports polling I/O via virtio-blk driver. Polling
> feature is enabled by module parameter "num_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
> "num_poll_queues". If VM sets queue parameter as below,
> ("num-queues=N" [QEMU property], "num_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
> 
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
>  drivers/block/virtio_blk.c | 112 +++++++++++++++++++++++++++++++++++--
>  1 file changed, 108 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 8c415be86732..c2d955da0006 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 num_poll_queues;
> +module_param(num_poll_queues, uint, 0644);
> +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
 
Sorry. I forgot to fix the parameter name.
I resended this path.

Regards,
Suwan Kim

Re: [PATCH v4 2/2] virtio-blk: support mq_ops->queue_rqs()

[Suwan Kim]

On Tue, Apr 05, 2022 at 01:57:06AM -0700, Christoph Hellwig wrote:
> On Tue, Apr 05, 2022 at 02:31:22PM +0900, 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
> > 
> > Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> > ---
> >  drivers/block/virtio_blk.c | 110 +++++++++++++++++++++++++++++++++----
> >  1 file changed, 99 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 712579dcd3cc..a091034bc551 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -92,6 +92,7 @@ struct virtio_blk {
> >  struct virtblk_req {
> >  	struct virtio_blk_outhdr out_hdr;
> >  	u8 status;
> > +	int sg_num;
> >  	struct sg_table sg_table;
> >  	struct scatterlist sg[];
> >  };
> > @@ -311,18 +312,13 @@ static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx)
> >  		virtqueue_notify(vq->vq);
> >  }
> >  
> > -static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> > -			   const struct blk_mq_queue_data *bd)
> > +static blk_status_t virtblk_prep_rq(struct blk_mq_hw_ctx *hctx,
> > +					struct virtio_blk *vblk,
> > +					struct request *req,
> > +					struct virtblk_req *vbr)
> >  {
> > -	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;
> > +	int num;
> >  
> >  	status = virtblk_setup_cmd(vblk->vdev, req, vbr);
> >  	if (unlikely(status))
> > @@ -335,9 +331,30 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> >  		virtblk_cleanup_cmd(req);
> >  		return BLK_STS_RESOURCE;
> >  	}
> > +	vbr->sg_num = num;
> 
> This can go into the nents field of vbr->sg_table.
> 
> > +	int err;
> > +
> > +	status = virtblk_prep_rq(hctx, vblk, req, vbr);
> > +	if (unlikely(status))
> > +		return status;
> >  
> >  	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,
> > +				vbr->sg_table.sgl, vbr->sg_num);
> 
> And while we're at it - virtblk_add_req can lose the data_sg and
> have_data arguments as they can be derived from vbr.

Ok. I will remove vbr->sg_num and save it to vbr->sg_table.nents.

Regards,
Suwan Kim

Re: [PATCH v4 2/2] virtio-blk: support mq_ops->queue_rqs()

[Stefan Hajnoczi]

[-- Attachment #1.1: Type: text/plain, Size: 2087 bytes --]

On Tue, Apr 05, 2022 at 02:31:22PM +0900, 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
> 
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
>  drivers/block/virtio_blk.c | 110 +++++++++++++++++++++++++++++++++----
>  1 file changed, 99 insertions(+), 11 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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[-- Attachment #2: Type: text/plain, Size: 183 bytes --]

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Re: [PATCH v4 2/2] virtio-blk: support mq_ops->queue_rqs()

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 2087 bytes --]

On Tue, Apr 05, 2022 at 02:31:22PM +0900, 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
> 
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
>  drivers/block/virtio_blk.c | 110 +++++++++++++++++++++++++++++++++----
>  1 file changed, 99 insertions(+), 11 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [PATCH v4 2/2] virtio-blk: support mq_ops->queue_rqs()

[Christoph Hellwig]

On Tue, Apr 05, 2022 at 02:31:22PM +0900, 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
> 
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
>  drivers/block/virtio_blk.c | 110 +++++++++++++++++++++++++++++++++----
>  1 file changed, 99 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 712579dcd3cc..a091034bc551 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -92,6 +92,7 @@ struct virtio_blk {
>  struct virtblk_req {
>  	struct virtio_blk_outhdr out_hdr;
>  	u8 status;
> +	int sg_num;
>  	struct sg_table sg_table;
>  	struct scatterlist sg[];
>  };
> @@ -311,18 +312,13 @@ static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx)
>  		virtqueue_notify(vq->vq);
>  }
>  
> -static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> -			   const struct blk_mq_queue_data *bd)
> +static blk_status_t virtblk_prep_rq(struct blk_mq_hw_ctx *hctx,
> +					struct virtio_blk *vblk,
> +					struct request *req,
> +					struct virtblk_req *vbr)
>  {
> -	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;
> +	int num;
>  
>  	status = virtblk_setup_cmd(vblk->vdev, req, vbr);
>  	if (unlikely(status))
> @@ -335,9 +331,30 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
>  		virtblk_cleanup_cmd(req);
>  		return BLK_STS_RESOURCE;
>  	}
> +	vbr->sg_num = num;

This can go into the nents field of vbr->sg_table.

> +	int err;
> +
> +	status = virtblk_prep_rq(hctx, vblk, req, vbr);
> +	if (unlikely(status))
> +		return status;
>  
>  	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,
> +				vbr->sg_table.sgl, vbr->sg_num);

And while we're at it - virtblk_add_req can lose the data_sg and
have_data arguments as they can be derived from vbr.
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Re: [PATCH v4 2/2] virtio-blk: support mq_ops->queue_rqs()

[Christoph Hellwig]

On Tue, Apr 05, 2022 at 02:31:22PM +0900, 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
> 
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
>  drivers/block/virtio_blk.c | 110 +++++++++++++++++++++++++++++++++----
>  1 file changed, 99 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 712579dcd3cc..a091034bc551 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -92,6 +92,7 @@ struct virtio_blk {
>  struct virtblk_req {
>  	struct virtio_blk_outhdr out_hdr;
>  	u8 status;
> +	int sg_num;
>  	struct sg_table sg_table;
>  	struct scatterlist sg[];
>  };
> @@ -311,18 +312,13 @@ static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx)
>  		virtqueue_notify(vq->vq);
>  }
>  
> -static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> -			   const struct blk_mq_queue_data *bd)
> +static blk_status_t virtblk_prep_rq(struct blk_mq_hw_ctx *hctx,
> +					struct virtio_blk *vblk,
> +					struct request *req,
> +					struct virtblk_req *vbr)
>  {
> -	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;
> +	int num;
>  
>  	status = virtblk_setup_cmd(vblk->vdev, req, vbr);
>  	if (unlikely(status))
> @@ -335,9 +331,30 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
>  		virtblk_cleanup_cmd(req);
>  		return BLK_STS_RESOURCE;
>  	}
> +	vbr->sg_num = num;

This can go into the nents field of vbr->sg_table.

> +	int err;
> +
> +	status = virtblk_prep_rq(hctx, vblk, req, vbr);
> +	if (unlikely(status))
> +		return status;
>  
>  	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,
> +				vbr->sg_table.sgl, vbr->sg_num);

And while we're at it - virtblk_add_req can lose the data_sg and
have_data arguments as they can be derived from vbr.

[PATCH v4 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

Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
---
 drivers/block/virtio_blk.c | 110 +++++++++++++++++++++++++++++++++----
 1 file changed, 99 insertions(+), 11 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 712579dcd3cc..a091034bc551 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -92,6 +92,7 @@ struct virtio_blk {
 struct virtblk_req {
 	struct virtio_blk_outhdr out_hdr;
 	u8 status;
+	int sg_num;
 	struct sg_table sg_table;
 	struct scatterlist sg[];
 };
@@ -311,18 +312,13 @@ static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx)
 		virtqueue_notify(vq->vq);
 }
 
-static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
-			   const struct blk_mq_queue_data *bd)
+static blk_status_t virtblk_prep_rq(struct blk_mq_hw_ctx *hctx,
+					struct virtio_blk *vblk,
+					struct request *req,
+					struct virtblk_req *vbr)
 {
-	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;
+	int num;
 
 	status = virtblk_setup_cmd(vblk->vdev, req, vbr);
 	if (unlikely(status))
@@ -335,9 +331,30 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
 		virtblk_cleanup_cmd(req);
 		return BLK_STS_RESOURCE;
 	}
+	vbr->sg_num = num;
+
+	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 qid = hctx->queue_num;
+	bool notify = false;
+	blk_status_t status;
+	int err;
+
+	status = virtblk_prep_rq(hctx, vblk, req, vbr);
+	if (unlikely(status))
+		return status;
 
 	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,
+				vbr->sg_table.sgl, vbr->sg_num);
 	if (err) {
 		virtqueue_kick(vblk->vqs[qid].vq);
 		/* Don't stop the queue if -ENOMEM: we may have failed to
@@ -367,6 +384,76 @@ 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,
+					vbr->sg_table.sgl, vbr->sg_num);
+		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)
@@ -834,6 +921,7 @@ 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