[PATCH 0/3][RFC] virtio-blk: add io_uring passthrough support for virtio-blk

[PATCH 0/3][RFC] virtio-blk: add io_uring passthrough support for virtio-blk

[Ferry Meng]

We seek to develop a more flexible way to use virtio-blk and bypass the block
layer logic in order to accomplish certain performance optimizations. As a
result, we referred to the implementation of io_uring passthrough in NVMe
and implemented it in the virtio-blk driver. This patch series adds io_uring
passthrough support for virtio-blk devices, resulting in lower submit latency
and increased flexibility when utilizing virtio-blk.

To test this patch series, I changed fio's code: 
1. Added virtio-blk support to engines/io_uring.c.
2. Added virtio-blk support to the t/io_uring.c testing tool.
Link: https://github.com/jdmfr/fio 

Using t/io_uring-vblk, the performance of virtio-blk based on uring-cmd
scales better than block device access. (such as below, Virtio-Blk with QEMU,
1-depth fio) 
(passthru) read: IOPS=17.2k, BW=67.4MiB/s (70.6MB/s) 
slat (nsec): min=2907, max=43592, avg=3981.87, stdev=595.10 
clat (usec): min=38, max=285,avg=53.47, stdev= 8.28 
lat (usec): min=44, max=288, avg=57.45, stdev= 8.28
(block) read: IOPS=15.3k, BW=59.8MiB/s (62.7MB/s) 
slat (nsec): min=3408, max=35366, avg=5102.17, stdev=790.79 
clat (usec): min=35, max=343, avg=59.63, stdev=10.26 
lat (usec): min=43, max=349, avg=64.73, stdev=10.21

Testing the virtio-blk device with fio using 'engines=io_uring_cmd'
and 'engines=io_uring' also demonstrates improvements in submit latency.
(passthru) taskset -c 0 t/io_uring-vblk -b4096 -d8 -c4 -s4 -p0 -F1 -B0 -O0 -n1 -u1 /dev/vdcc0 
IOPS=189.80K, BW=741MiB/s, IOS/call=4/3
IOPS=187.68K, BW=733MiB/s, IOS/call=4/3 
(block) taskset -c 0 t/io_uring-vblk -b4096 -d8 -c4 -s4 -p0 -F1 -B0 -O0 -n1 -u0 /dev/vdc 
IOPS=101.51K, BW=396MiB/s, IOS/call=4/3
IOPS=100.01K, BW=390MiB/s, IOS/call=4/4

The performance overhead of submitting IO can be decreased by 25% overall
with this patch series. The implementation primarily references 'nvme io_uring
passthrough', supporting io_uring_cmd through a separate character interface
(temporarily named /dev/vdXc0). Since this is an early version, many
details need to be taken into account and redesigned, like:
● Currently, it only considers READ/WRITE scenarios, some more complex operations 
not included like discard or zone ops.(Normal sqe64 is sufficient, in my opinion;
following upgrades, sqe128 and cqe32 might not be needed).
● ......

I would appreciate any useful recommendations.

Ferry Meng (3):
  virtio-blk: add virtio-blk chardev support.
  virtio-blk: add uring_cmd support for I/O passthru on chardev.
  virtio-blk: add uring_cmd iopoll support.

 drivers/block/virtio_blk.c      | 325 +++++++++++++++++++++++++++++++-
 include/uapi/linux/virtio_blk.h |  16 ++
 2 files changed, 336 insertions(+), 5 deletions(-)

-- 
2.43.5

[PATCH 1/3] virtio-blk: add virtio-blk chardev support.

[Ferry Meng]

Introduce character interfaces for block device (per-device), facilitating
access to block devices through io_uring I/O passsthrough.

Besides, vblk initialize only use kmalloc with GFP_KERNEL flag, but for
char device support, we should ensure cdev kobj must be zero before
initialize. So better initial this struct with __GFP_ZERO flag.

Now the character devices only named as

	- /dev/vdXc0

Currently, only one character interface is created for one actual
virtblk device, although it has been partitioned.

Signed-off-by: Ferry Meng <mengferry@linux.alibaba.com>
---
 drivers/block/virtio_blk.c | 84 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 83 insertions(+), 1 deletion(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 194417abc105..3487aaa67514 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -17,6 +17,7 @@
 #include <linux/numa.h>
 #include <linux/vmalloc.h>
 #include <uapi/linux/virtio_ring.h>
+#include <linux/cdev.h>
 
 #define PART_BITS 4
 #define VQ_NAME_LEN 16
@@ -25,6 +26,8 @@
 /* The maximum number of sg elements that fit into a virtqueue */
 #define VIRTIO_BLK_MAX_SG_ELEMS 32768
 
+#define VIRTBLK_MINORS		(1U << MINORBITS)
+
 #ifdef CONFIG_ARCH_NO_SG_CHAIN
 #define VIRTIO_BLK_INLINE_SG_CNT	0
 #else
@@ -45,6 +48,10 @@ MODULE_PARM_DESC(poll_queues, "The number of dedicated virtqueues for polling I/
 static int major;
 static DEFINE_IDA(vd_index_ida);
 
+static DEFINE_IDA(vd_chr_minor_ida);
+static dev_t vd_chr_devt;
+static struct class *vd_chr_class;
+
 static struct workqueue_struct *virtblk_wq;
 
 struct virtio_blk_vq {
@@ -84,6 +91,10 @@ struct virtio_blk {
 
 	/* For zoned device */
 	unsigned int zone_sectors;
+
+	/* For passthrough cmd */
+	struct cdev cdev;
+	struct device cdev_device;
 };
 
 struct virtblk_req {
@@ -1239,6 +1250,55 @@ static const struct blk_mq_ops virtio_mq_ops = {
 	.poll		= virtblk_poll,
 };
 
+static void virtblk_cdev_rel(struct device *dev)
+{
+	ida_free(&vd_chr_minor_ida, MINOR(dev->devt));
+}
+
+static void virtblk_cdev_del(struct cdev *cdev, struct device *cdev_device)
+{
+	cdev_device_del(cdev, cdev_device);
+	put_device(cdev_device);
+}
+
+static int virtblk_cdev_add(struct virtio_blk *vblk,
+		const struct file_operations *fops)
+{
+	struct cdev *cdev = &vblk->cdev;
+	struct device *cdev_device = &vblk->cdev_device;
+	int minor, ret;
+
+	minor = ida_alloc(&vd_chr_minor_ida, GFP_KERNEL);
+	if (minor < 0)
+		return minor;
+
+	cdev_device->parent = &vblk->vdev->dev;
+	cdev_device->devt = MKDEV(MAJOR(vd_chr_devt), minor);
+	cdev_device->class = vd_chr_class;
+	cdev_device->release = virtblk_cdev_rel;
+	device_initialize(cdev_device);
+
+	ret = dev_set_name(cdev_device, "%sc0", vblk->disk->disk_name);
+	if (ret)
+		goto err;
+
+	cdev_init(cdev, fops);
+	ret = cdev_device_add(cdev, cdev_device);
+	if (ret) {
+		put_device(cdev_device);
+		goto err;
+	}
+	return ret;
+
+err:
+	ida_free(&vd_chr_minor_ida, minor);
+	return ret;
+}
+
+static const struct file_operations virtblk_chr_fops = {
+	.owner		= THIS_MODULE,
+};
+
 static unsigned int virtblk_queue_depth;
 module_param_named(queue_depth, virtblk_queue_depth, uint, 0444);
 
@@ -1456,7 +1516,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 		goto out;
 	index = err;
 
-	vdev->priv = vblk = kmalloc(sizeof(*vblk), GFP_KERNEL);
+	vdev->priv = vblk = kzalloc(sizeof(*vblk), GFP_KERNEL);
 	if (!vblk) {
 		err = -ENOMEM;
 		goto out_free_index;
@@ -1544,6 +1604,10 @@ static int virtblk_probe(struct virtio_device *vdev)
 	if (err)
 		goto out_cleanup_disk;
 
+	err = virtblk_cdev_add(vblk, &virtblk_chr_fops);
+	if (err)
+		goto out_cleanup_disk;
+
 	return 0;
 
 out_cleanup_disk:
@@ -1568,6 +1632,8 @@ static void virtblk_remove(struct virtio_device *vdev)
 	/* Make sure no work handler is accessing the device. */
 	flush_work(&vblk->config_work);
 
+	virtblk_cdev_del(&vblk->cdev, &vblk->cdev_device);
+
 	del_gendisk(vblk->disk);
 	blk_mq_free_tag_set(&vblk->tag_set);
 
@@ -1674,13 +1740,27 @@ static int __init virtio_blk_init(void)
 		goto out_destroy_workqueue;
 	}
 
+	error = alloc_chrdev_region(&vd_chr_devt, 0, VIRTBLK_MINORS,
+				"vblk-generic");
+	if (error < 0)
+		goto unregister_chrdev;
+
+	vd_chr_class = class_create("vblk-generic");
+	if (IS_ERR(vd_chr_class)) {
+		error = PTR_ERR(vd_chr_class);
+		goto unregister_chrdev;
+	}
+
 	error = register_virtio_driver(&virtio_blk);
 	if (error)
 		goto out_unregister_blkdev;
+
 	return 0;
 
 out_unregister_blkdev:
 	unregister_blkdev(major, "virtblk");
+unregister_chrdev:
+	unregister_chrdev_region(vd_chr_devt, VIRTBLK_MINORS);
 out_destroy_workqueue:
 	destroy_workqueue(virtblk_wq);
 	return error;
@@ -1690,7 +1770,9 @@ static void __exit virtio_blk_fini(void)
 {
 	unregister_virtio_driver(&virtio_blk);
 	unregister_blkdev(major, "virtblk");
+	unregister_chrdev_region(vd_chr_devt, VIRTBLK_MINORS);
 	destroy_workqueue(virtblk_wq);
+	ida_destroy(&vd_chr_minor_ida);
 }
 module_init(virtio_blk_init);
 module_exit(virtio_blk_fini);
-- 
2.43.5

[PATCH 2/3] virtio-blk: add uring_cmd support for I/O passthru on chardev.

[Ferry Meng]

Add ->uring_cmd() support for virtio-blk chardev (/dev/vdXc0).
According to virtio spec, in addition to passing 'hdr' info into kernel,
we also need to pass vaddr & data length of the 'iov' requeired for the
writev/readv op.

Signed-off-by: Ferry Meng <mengferry@linux.alibaba.com>
---
 drivers/block/virtio_blk.c      | 228 +++++++++++++++++++++++++++++++-
 include/uapi/linux/virtio_blk.h |  16 +++
 2 files changed, 240 insertions(+), 4 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 3487aaa67514..1a4bac3dc044 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -18,6 +18,9 @@
 #include <linux/vmalloc.h>
 #include <uapi/linux/virtio_ring.h>
 #include <linux/cdev.h>
+#include <linux/io_uring/cmd.h>
+#include <linux/types.h>
+#include <linux/uio.h>
 
 #define PART_BITS 4
 #define VQ_NAME_LEN 16
@@ -54,6 +57,20 @@ static struct class *vd_chr_class;
 
 static struct workqueue_struct *virtblk_wq;
 
+struct virtblk_uring_cmd_pdu {
+	struct request *req;
+	struct bio *bio;
+	int status;
+};
+
+struct virtblk_command {
+	struct virtio_blk_outhdr out_hdr;
+
+	__u64	data;
+	__u32	data_len;
+	__u32	flag;
+};
+
 struct virtio_blk_vq {
 	struct virtqueue *vq;
 	spinlock_t lock;
@@ -122,6 +139,16 @@ struct virtblk_req {
 	struct scatterlist sg[];
 };
 
+static bool virtblk_is_write(struct virtblk_command *cmd)
+{
+	return cmd->out_hdr.type & VIRTIO_BLK_T_OUT;
+}
+
+static void __user *virtblk_to_user_ptr(uintptr_t ptrval)
+{
+	return (void __user *)ptrval;
+}
+
 static inline blk_status_t virtblk_result(u8 status)
 {
 	switch (status) {
@@ -259,9 +286,6 @@ static blk_status_t virtblk_setup_cmd(struct virtio_device *vdev,
 	if (!IS_ENABLED(CONFIG_BLK_DEV_ZONED) && op_is_zone_mgmt(req_op(req)))
 		return BLK_STS_NOTSUPP;
 
-	/* Set fields for all request types */
-	vbr->out_hdr.ioprio = cpu_to_virtio32(vdev, req_get_ioprio(req));
-
 	switch (req_op(req)) {
 	case REQ_OP_READ:
 		type = VIRTIO_BLK_T_IN;
@@ -309,9 +333,11 @@ static blk_status_t virtblk_setup_cmd(struct virtio_device *vdev,
 		type = VIRTIO_BLK_T_ZONE_RESET_ALL;
 		break;
 	case REQ_OP_DRV_IN:
+	case REQ_OP_DRV_OUT:
 		/*
 		 * Out header has already been prepared by the caller (virtblk_get_id()
-		 * or virtblk_submit_zone_report()), nothing to do here.
+		 * virtblk_submit_zone_report() or io_uring passthrough cmd), nothing
+		 * to do here.
 		 */
 		return 0;
 	default:
@@ -323,6 +349,7 @@ static blk_status_t virtblk_setup_cmd(struct virtio_device *vdev,
 	vbr->in_hdr_len = in_hdr_len;
 	vbr->out_hdr.type = cpu_to_virtio32(vdev, type);
 	vbr->out_hdr.sector = cpu_to_virtio64(vdev, sector);
+	vbr->out_hdr.ioprio = cpu_to_virtio32(vdev, req_get_ioprio(req));
 
 	if (type == VIRTIO_BLK_T_DISCARD || type == VIRTIO_BLK_T_WRITE_ZEROES ||
 	    type == VIRTIO_BLK_T_SECURE_ERASE) {
@@ -832,6 +859,7 @@ static int virtblk_get_id(struct gendisk *disk, char *id_str)
 	vbr = blk_mq_rq_to_pdu(req);
 	vbr->in_hdr_len = sizeof(vbr->in_hdr.status);
 	vbr->out_hdr.type = cpu_to_virtio32(vblk->vdev, VIRTIO_BLK_T_GET_ID);
+	vbr->out_hdr.ioprio = cpu_to_virtio32(vblk->vdev, req_get_ioprio(req));
 	vbr->out_hdr.sector = 0;
 
 	err = blk_rq_map_kern(q, req, id_str, VIRTIO_BLK_ID_BYTES, GFP_KERNEL);
@@ -1250,6 +1278,197 @@ static const struct blk_mq_ops virtio_mq_ops = {
 	.poll		= virtblk_poll,
 };
 
+static inline struct virtblk_uring_cmd_pdu *virtblk_get_uring_cmd_pdu(
+		struct io_uring_cmd *ioucmd)
+{
+	return (struct virtblk_uring_cmd_pdu *)&ioucmd->pdu;
+}
+
+static void virtblk_uring_task_cb(struct io_uring_cmd *ioucmd,
+		unsigned int issue_flags)
+{
+	struct virtblk_uring_cmd_pdu *pdu = virtblk_get_uring_cmd_pdu(ioucmd);
+	struct virtblk_req *vbr = blk_mq_rq_to_pdu(pdu->req);
+	u64 result = 0;
+
+	if (pdu->bio)
+		blk_rq_unmap_user(pdu->bio);
+
+	/* currently result has no use, it should be zero as cqe->res */
+	io_uring_cmd_done(ioucmd, vbr->in_hdr.status, result, issue_flags);
+}
+
+static enum rq_end_io_ret virtblk_uring_cmd_end_io(struct request *req,
+						   blk_status_t err)
+{
+	struct io_uring_cmd *ioucmd = req->end_io_data;
+	struct virtblk_uring_cmd_pdu *pdu = virtblk_get_uring_cmd_pdu(ioucmd);
+
+	/*
+	 * For iopoll, complete it directly. Note that using the uring_cmd
+	 * helper for this is safe only because we check blk_rq_is_poll().
+	 * As that returns false if we're NOT on a polled queue, then it's
+	 * safe to use the polled completion helper.
+	 *
+	 * Otherwise, move the completion to task work.
+	 */
+	if (blk_rq_is_poll(req)) {
+		if (pdu->bio)
+			blk_rq_unmap_user(pdu->bio);
+		io_uring_cmd_iopoll_done(ioucmd, 0, pdu->status);
+	} else {
+		io_uring_cmd_do_in_task_lazy(ioucmd, virtblk_uring_task_cb);
+	}
+
+	return RQ_END_IO_FREE;
+}
+
+static struct virtblk_req *virtblk_req(struct request *req)
+{
+	return blk_mq_rq_to_pdu(req);
+}
+
+static enum req_op virtblk_req_op(struct virtblk_command *cmd)
+{
+	return virtblk_is_write(cmd) ? REQ_OP_DRV_OUT : REQ_OP_DRV_IN;
+}
+
+static struct request *virtblk_alloc_user_request(
+		struct request_queue *q, struct virtblk_command *cmd,
+		unsigned int rq_flags, blk_mq_req_flags_t blk_flags)
+{
+	struct request *req;
+
+	req = blk_mq_alloc_request(q, virtblk_req_op(cmd) | rq_flags, blk_flags);
+	if (IS_ERR(req))
+		return req;
+
+	req->rq_flags |= RQF_DONTPREP;
+	memcpy(&virtblk_req(req)->out_hdr, &cmd->out_hdr, sizeof(struct virtio_blk_outhdr));
+	return req;
+}
+
+static int virtblk_map_user_request(struct request *req, u64 ubuffer,
+		unsigned int bufflen, struct io_uring_cmd *ioucmd,
+		bool vec)
+{
+	struct request_queue *q = req->q;
+	struct virtio_blk *vblk = q->queuedata;
+	struct block_device *bdev = vblk ? vblk->disk->part0 : NULL;
+	struct bio *bio = NULL;
+	int ret;
+
+	if (ioucmd && (ioucmd->flags & IORING_URING_CMD_FIXED)) {
+		struct iov_iter iter;
+
+		/* fixedbufs is only for non-vectored io */
+		if (WARN_ON_ONCE(vec))
+			return -EINVAL;
+		ret = io_uring_cmd_import_fixed(ubuffer, bufflen,
+				rq_data_dir(req), &iter, ioucmd);
+		if (ret < 0)
+			goto out;
+		ret = blk_rq_map_user_iov(q, req, NULL,
+			&iter, GFP_KERNEL);
+	} else {
+		ret = blk_rq_map_user_io(req, NULL,
+				virtblk_to_user_ptr(ubuffer),
+				bufflen, GFP_KERNEL, vec, 0,
+				0, rq_data_dir(req));
+	}
+	if (ret)
+		goto out;
+
+	bio = req->bio;
+	if (bdev)
+		bio_set_dev(bio, bdev);
+	return 0;
+
+out:
+	blk_mq_free_request(req);
+	return ret;
+}
+
+static int virtblk_uring_cmd_io(struct virtio_blk *vblk,
+		struct io_uring_cmd *ioucmd, unsigned int issue_flags, bool vec)
+{
+	struct virtblk_uring_cmd_pdu *pdu = virtblk_get_uring_cmd_pdu(ioucmd);
+	const struct virtblk_uring_cmd *cmd = io_uring_sqe_cmd(ioucmd->sqe);
+	struct request_queue *q = vblk->disk->queue;
+	struct virtblk_req *vbr;
+	struct virtblk_command d;
+	struct request *req;
+	unsigned int rq_flags = 0;
+	blk_mq_req_flags_t blk_flags = 0;
+	int ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EACCES;
+
+	d.out_hdr.ioprio = cpu_to_virtio32(vblk->vdev, READ_ONCE(cmd->ioprio));
+	d.out_hdr.type = cpu_to_virtio32(vblk->vdev, READ_ONCE(cmd->type));
+	d.out_hdr.sector = cpu_to_virtio32(vblk->vdev, READ_ONCE(cmd->sector));
+	d.data = READ_ONCE(cmd->data);
+	d.data_len = READ_ONCE(cmd->data_len);
+
+	if (issue_flags & IO_URING_F_NONBLOCK) {
+		rq_flags = REQ_NOWAIT;
+		blk_flags = BLK_MQ_REQ_NOWAIT;
+	}
+	if (issue_flags & IO_URING_F_IOPOLL)
+		rq_flags |= REQ_POLLED;
+
+	req = virtblk_alloc_user_request(q, &d, rq_flags, blk_flags);
+	if (IS_ERR(req))
+		return PTR_ERR(req);
+
+	vbr = virtblk_req(req);
+	vbr->in_hdr_len = sizeof(vbr->in_hdr.status);
+	if (d.data && d.data_len) {
+		ret = virtblk_map_user_request(req, d.data, d.data_len, ioucmd, vec);
+		if (ret)
+			return ret;
+	}
+
+	/* to free bio on completion, as req->bio will be null at that time */
+	pdu->bio = req->bio;
+	pdu->req = req;
+	req->end_io_data = ioucmd;
+	req->end_io = virtblk_uring_cmd_end_io;
+	blk_execute_rq_nowait(req, false);
+	return -EIOCBQUEUED;
+}
+
+
+static int virtblk_uring_cmd(struct virtio_blk *vblk, struct io_uring_cmd *ioucmd,
+			     unsigned int issue_flags)
+{
+	int ret;
+
+	BUILD_BUG_ON(sizeof(struct virtblk_uring_cmd_pdu) > sizeof(ioucmd->pdu));
+
+	switch (ioucmd->cmd_op) {
+	case VIRTBLK_URING_CMD_IO:
+		ret = virtblk_uring_cmd_io(vblk, ioucmd, issue_flags, false);
+		break;
+	case VIRTBLK_URING_CMD_IO_VEC:
+		ret = virtblk_uring_cmd_io(vblk, ioucmd, issue_flags, true);
+		break;
+	default:
+		ret = -ENOTTY;
+	}
+
+	return ret;
+}
+
+static int virtblk_chr_uring_cmd(struct io_uring_cmd *ioucmd, unsigned int issue_flags)
+{
+	struct virtio_blk *vblk = container_of(file_inode(ioucmd->file)->i_cdev,
+			struct virtio_blk, cdev);
+
+	return virtblk_uring_cmd(vblk, ioucmd, issue_flags);
+}
+
 static void virtblk_cdev_rel(struct device *dev)
 {
 	ida_free(&vd_chr_minor_ida, MINOR(dev->devt));
@@ -1297,6 +1516,7 @@ static int virtblk_cdev_add(struct virtio_blk *vblk,
 
 static const struct file_operations virtblk_chr_fops = {
 	.owner		= THIS_MODULE,
+	.uring_cmd	= virtblk_chr_uring_cmd,
 };
 
 static unsigned int virtblk_queue_depth;
diff --git a/include/uapi/linux/virtio_blk.h b/include/uapi/linux/virtio_blk.h
index 3744e4da1b2a..93b6e1b5b9a4 100644
--- a/include/uapi/linux/virtio_blk.h
+++ b/include/uapi/linux/virtio_blk.h
@@ -313,6 +313,22 @@ struct virtio_scsi_inhdr {
 };
 #endif /* !VIRTIO_BLK_NO_LEGACY */
 
+struct virtblk_uring_cmd {
+	/* VIRTIO_BLK_T* */
+	__u32 type;
+	/* io priority. */
+	__u32 ioprio;
+	/* Sector (ie. 512 byte offset) */
+	__u64 sector;
+
+	__u64 data;
+	__u32 data_len;
+	__u32 flag;
+};
+
+#define VIRTBLK_URING_CMD_IO		1
+#define VIRTBLK_URING_CMD_IO_VEC	2
+
 /* And this is the final byte of the write scatter-gather list. */
 #define VIRTIO_BLK_S_OK		0
 #define VIRTIO_BLK_S_IOERR	1
-- 
2.43.5

[PATCH 3/3] virtio-blk: add uring_cmd iopoll support.

[Ferry Meng]

Add polling support for uring_cmd polling support for virtblk, which
will be called during completion-polling.

Signed-off-by: Ferry Meng <mengferry@linux.alibaba.com>
---
 drivers/block/virtio_blk.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 1a4bac3dc044..7888789a3eb8 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -1469,6 +1469,18 @@ static int virtblk_chr_uring_cmd(struct io_uring_cmd *ioucmd, unsigned int issue
 	return virtblk_uring_cmd(vblk, ioucmd, issue_flags);
 }
 
+static int virtblk_chr_uring_cmd_iopoll(struct io_uring_cmd *ioucmd,
+				 struct io_comp_batch *iob,
+				 unsigned int poll_flags)
+{
+	struct virtblk_uring_cmd_pdu *pdu = virtblk_get_uring_cmd_pdu(ioucmd);
+	struct request *req = pdu->req;
+
+	if (req && blk_rq_is_poll(req))
+		return blk_rq_poll(req, iob, poll_flags);
+	return 0;
+}
+
 static void virtblk_cdev_rel(struct device *dev)
 {
 	ida_free(&vd_chr_minor_ida, MINOR(dev->devt));
@@ -1517,6 +1529,7 @@ static int virtblk_cdev_add(struct virtio_blk *vblk,
 static const struct file_operations virtblk_chr_fops = {
 	.owner		= THIS_MODULE,
 	.uring_cmd	= virtblk_chr_uring_cmd,
+	.uring_cmd_iopoll = virtblk_chr_uring_cmd_iopoll,
 };
 
 static unsigned int virtblk_queue_depth;
-- 
2.43.5

Re: [PATCH 2/3] virtio-blk: add uring_cmd support for I/O passthru on chardev.

[kernel test robot]

Hi Ferry,

kernel test robot noticed the following build warnings:

[auto build test WARNING on axboe-block/for-next]
[also build test WARNING on linus/master v6.13-rc1 next-20241203]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Ferry-Meng/virtio-blk-add-virtio-blk-chardev-support/20241203-202032
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
patch link:    https://lore.kernel.org/r/20241203121424.19887-3-mengferry%40linux.alibaba.com
patch subject: [PATCH 2/3] virtio-blk: add uring_cmd support for I/O passthru on chardev.
config: i386-randconfig-063-20241204 (https://download.01.org/0day-ci/archive/20241204/202412042324.uKQ5KdkE-lkp@intel.com/config)
compiler: clang version 19.1.3 (https://github.com/llvm/llvm-project ab51eccf88f5321e7c60591c5546b254b6afab99)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241204/202412042324.uKQ5KdkE-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202412042324.uKQ5KdkE-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> drivers/block/virtio_blk.c:144:28: sparse: sparse: restricted __virtio32 degrades to integer
>> drivers/block/virtio_blk.c:1337:53: sparse: sparse: restricted blk_opf_t degrades to integer
>> drivers/block/virtio_blk.c:1337:59: sparse: sparse: incorrect type in argument 2 (different base types) @@     expected restricted blk_opf_t [usertype] opf @@     got unsigned int @@
   drivers/block/virtio_blk.c:1337:59: sparse:     expected restricted blk_opf_t [usertype] opf
   drivers/block/virtio_blk.c:1337:59: sparse:     got unsigned int
>> drivers/block/virtio_blk.c:1405:26: sparse: sparse: incorrect type in assignment (different base types) @@     expected restricted __virtio64 [assigned] [usertype] sector @@     got restricted __virtio32 @@
   drivers/block/virtio_blk.c:1405:26: sparse:     expected restricted __virtio64 [assigned] [usertype] sector
   drivers/block/virtio_blk.c:1405:26: sparse:     got restricted __virtio32
>> drivers/block/virtio_blk.c:1410:26: sparse: sparse: incorrect type in assignment (different base types) @@     expected unsigned int rq_flags @@     got restricted blk_opf_t [usertype] @@
   drivers/block/virtio_blk.c:1410:26: sparse:     expected unsigned int rq_flags
   drivers/block/virtio_blk.c:1410:26: sparse:     got restricted blk_opf_t [usertype]
>> drivers/block/virtio_blk.c:1414:26: sparse: sparse: invalid assignment: |=
   drivers/block/virtio_blk.c:1414:26: sparse:    left side has type unsigned int
   drivers/block/virtio_blk.c:1414:26: sparse:    right side has type restricted blk_opf_t
   drivers/block/virtio_blk.c: note: in included file (through include/linux/mmzone.h, include/linux/gfp.h, include/linux/slab.h):
   include/linux/page-flags.h:237:46: sparse: sparse: self-comparison always evaluates to false
   include/linux/page-flags.h:237:46: sparse: sparse: self-comparison always evaluates to false

vim +144 drivers/block/virtio_blk.c

   141	
   142	static bool virtblk_is_write(struct virtblk_command *cmd)
   143	{
 > 144		return cmd->out_hdr.type & VIRTIO_BLK_T_OUT;
   145	}
   146	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 0/3][RFC] virtio-blk: add io_uring passthrough support for virtio-blk

[Stefan Hajnoczi]

On Tue, 3 Dec 2024 at 07:17, Ferry Meng <mengferry@linux.alibaba.com> wrote:
>
> We seek to develop a more flexible way to use virtio-blk and bypass the block
> layer logic in order to accomplish certain performance optimizations. As a
> result, we referred to the implementation of io_uring passthrough in NVMe
> and implemented it in the virtio-blk driver. This patch series adds io_uring
> passthrough support for virtio-blk devices, resulting in lower submit latency
> and increased flexibility when utilizing virtio-blk.

First I thought this was similar to Stefano Garzarella's previous
virtio-blk io_uring passthrough work where a host io_uring was passed
through into the guest:
https://static.sched.com/hosted_files/kvmforum2020/9c/KVMForum_2020_io_uring_passthrough_Stefano_Garzarella.pdf

But now I see this is a uring_cmd interface for sending virtio_blk
commands from userspace like the one offered by the NVMe driver.

Unlike NVMe, the virtio-blk command set is minimal and does not offer
a rich set of features. Is the motivation really virtio-blk command
passthrough or is the goal just to create a fast path for I/O?

If the goal is just a fast path for I/O, then maybe Jens would
consider a generic command set that is not device-specific? That way
any driver (NVMe, virtio-blk, etc) can implement this uring_cmd
interface and any application can use it without worrying about the
underlying command set. I think a generic fast path would be much more
useful to applications than driver-specific interfaces.

>
> To test this patch series, I changed fio's code:
> 1. Added virtio-blk support to engines/io_uring.c.
> 2. Added virtio-blk support to the t/io_uring.c testing tool.
> Link: https://github.com/jdmfr/fio
>
> Using t/io_uring-vblk, the performance of virtio-blk based on uring-cmd
> scales better than block device access. (such as below, Virtio-Blk with QEMU,
> 1-depth fio)
> (passthru) read: IOPS=17.2k, BW=67.4MiB/s (70.6MB/s)
> slat (nsec): min=2907, max=43592, avg=3981.87, stdev=595.10
> clat (usec): min=38, max=285,avg=53.47, stdev= 8.28
> lat (usec): min=44, max=288, avg=57.45, stdev= 8.28
> (block) read: IOPS=15.3k, BW=59.8MiB/s (62.7MB/s)
> slat (nsec): min=3408, max=35366, avg=5102.17, stdev=790.79
> clat (usec): min=35, max=343, avg=59.63, stdev=10.26
> lat (usec): min=43, max=349, avg=64.73, stdev=10.21
>
> Testing the virtio-blk device with fio using 'engines=io_uring_cmd'
> and 'engines=io_uring' also demonstrates improvements in submit latency.
> (passthru) taskset -c 0 t/io_uring-vblk -b4096 -d8 -c4 -s4 -p0 -F1 -B0 -O0 -n1 -u1 /dev/vdcc0
> IOPS=189.80K, BW=741MiB/s, IOS/call=4/3
> IOPS=187.68K, BW=733MiB/s, IOS/call=4/3
> (block) taskset -c 0 t/io_uring-vblk -b4096 -d8 -c4 -s4 -p0 -F1 -B0 -O0 -n1 -u0 /dev/vdc
> IOPS=101.51K, BW=396MiB/s, IOS/call=4/3
> IOPS=100.01K, BW=390MiB/s, IOS/call=4/4
>
> The performance overhead of submitting IO can be decreased by 25% overall
> with this patch series. The implementation primarily references 'nvme io_uring
> passthrough', supporting io_uring_cmd through a separate character interface
> (temporarily named /dev/vdXc0). Since this is an early version, many
> details need to be taken into account and redesigned, like:
> ● Currently, it only considers READ/WRITE scenarios, some more complex operations
> not included like discard or zone ops.(Normal sqe64 is sufficient, in my opinion;
> following upgrades, sqe128 and cqe32 might not be needed).
> ● ......
>
> I would appreciate any useful recommendations.
>
> Ferry Meng (3):
>   virtio-blk: add virtio-blk chardev support.
>   virtio-blk: add uring_cmd support for I/O passthru on chardev.
>   virtio-blk: add uring_cmd iopoll support.
>
>  drivers/block/virtio_blk.c      | 325 +++++++++++++++++++++++++++++++-
>  include/uapi/linux/virtio_blk.h |  16 ++
>  2 files changed, 336 insertions(+), 5 deletions(-)
>
> --
> 2.43.5
>
>