block/rnbd-clt: Support polling mode for IO latency optimization

RNBD can make double-queues for irq-mode and poll-mode.
For example, on 4-CPU system 8 request-queues are created,
4 for irq-mode and 4 for poll-mode.
If the IO has HIPRI flag, the block-layer will call .poll function
of RNBD. Then IO is sent to the poll-mode queue.
Add optional nr_poll_queues argument for map_devices interface.

To support polling of RNBD, RTRS client creates connections
for both of irq-mode and direct-poll-mode.

For example, on 4-CPU system it could've create 5 connections:
con[0] => user message (softirq cq)
con[1:4] => softirq cq

After this patch, it can create 9 connections:
con[0] => user message (softirq cq)
con[1:4] => softirq cq
con[5:8] => DIRECT-POLL cq

Cc: Leon Romanovsky <leonro@nvidia.com>
Cc: linux-rdma@vger.kernel.org
Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Acked-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/20210419073722.15351-14-gi-oh.kim@ionos.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

3 files changed, 129 insertions, 20 deletions

diff --git a/drivers/block/rnbd/rnbd-clt-sysfs.c b/drivers/block/rnbd/rnbd-clt-sysfs.c
index 49015f428e67..2b6305ecfd5f 100644
--- a/drivers/block/rnbd/rnbd-clt-sysfs.c
+++ b/drivers/block/rnbd/rnbd-clt-sysfs.c
@@ -34,6 +34,7 @@ enum {
 	RNBD_OPT_DEV_PATH	= 1 << 2,
 	RNBD_OPT_ACCESS_MODE	= 1 << 3,
 	RNBD_OPT_SESSNAME	= 1 << 6,
+	RNBD_OPT_NR_POLL_QUEUES	= 1 << 7,
 };
 
 static const unsigned int rnbd_opt_mandatory[] = {
@@ -42,12 +43,13 @@ static const unsigned int rnbd_opt_mandatory[] = {
 };
 
 static const match_table_t rnbd_opt_tokens = {
-	{RNBD_OPT_PATH,		"path=%s"	},
-	{RNBD_OPT_DEV_PATH,	"device_path=%s"},
-	{RNBD_OPT_DEST_PORT,	"dest_port=%d"  },
-	{RNBD_OPT_ACCESS_MODE,	"access_mode=%s"},
-	{RNBD_OPT_SESSNAME,	"sessname=%s"	},
-	{RNBD_OPT_ERR,		NULL		},
+	{RNBD_OPT_PATH,			"path=%s"		},
+	{RNBD_OPT_DEV_PATH,		"device_path=%s"	},
+	{RNBD_OPT_DEST_PORT,		"dest_port=%d"		},
+	{RNBD_OPT_ACCESS_MODE,		"access_mode=%s"	},
+	{RNBD_OPT_SESSNAME,		"sessname=%s"		},
+	{RNBD_OPT_NR_POLL_QUEUES,	"nr_poll_queues=%d"	},
+	{RNBD_OPT_ERR,			NULL			},
 };
 
 struct rnbd_map_options {
@@ -57,6 +59,7 @@ struct rnbd_map_options {
 	char *pathname;
 	u16 *dest_port;
 	enum rnbd_access_mode *access_mode;
+	u32 *nr_poll_queues;
 };
 
 static int rnbd_clt_parse_map_options(const char *buf, size_t max_path_cnt,
@@ -68,7 +71,7 @@ static int rnbd_clt_parse_map_options(const char *buf, size_t max_path_cnt,
 	int opt_mask = 0;
 	int token;
 	int ret = -EINVAL;
-	int i, dest_port;
+	int i, dest_port, nr_poll_queues;
 	int p_cnt = 0;
 
 	options = kstrdup(buf, GFP_KERNEL);
@@ -178,6 +181,19 @@ static int rnbd_clt_parse_map_options(const char *buf, size_t max_path_cnt,
 			kfree(p);
 			break;
 
+		case RNBD_OPT_NR_POLL_QUEUES:
+			if (match_int(args, &nr_poll_queues) || nr_poll_queues < -1 ||
+			    nr_poll_queues > (int)nr_cpu_ids) {
+				pr_err("bad nr_poll_queues parameter '%d'\n",
+				       nr_poll_queues);
+				ret = -EINVAL;
+				goto out;
+			}
+			if (nr_poll_queues == -1)
+				nr_poll_queues = nr_cpu_ids;
+			*opt->nr_poll_queues = nr_poll_queues;
+			break;
+
 		default:
 			pr_err("map_device: Unknown parameter or missing value '%s'\n",
 			       p);
@@ -227,6 +243,19 @@ static ssize_t state_show(struct kobject *kobj,
 
 static struct kobj_attribute rnbd_clt_state_attr = __ATTR_RO(state);
 
+static ssize_t nr_poll_queues_show(struct kobject *kobj,
+				   struct kobj_attribute *attr, char *page)
+{
+	struct rnbd_clt_dev *dev;
+
+	dev = container_of(kobj, struct rnbd_clt_dev, kobj);
+
+	return sysfs_emit(page, "%d\n", dev->nr_poll_queues);
+}
+
+static struct kobj_attribute rnbd_clt_nr_poll_queues =
+	__ATTR_RO(nr_poll_queues);
+
 static ssize_t mapping_path_show(struct kobject *kobj,
 				 struct kobj_attribute *attr, char *page)
 {
@@ -421,6 +450,7 @@ static struct attribute *rnbd_dev_attrs[] = {
 	&rnbd_clt_state_attr.attr,
 	&rnbd_clt_session_attr.attr,
 	&rnbd_clt_access_mode.attr,
+	&rnbd_clt_nr_poll_queues.attr,
 	NULL,
 };
 
@@ -469,7 +499,7 @@ static ssize_t rnbd_clt_map_device_show(struct kobject *kobj,
 					 char *page)
 {
 	return scnprintf(page, PAGE_SIZE,
-			 "Usage: echo \"[dest_port=server port number] sessname=<name of the rtrs session> path=<[srcaddr@]dstaddr> [path=<[srcaddr@]dstaddr>] device_path=<full path on remote side> [access_mode=<ro|rw|migration>]\" > %s\n\naddr ::= [ ip:<ipv4> | ip:<ipv6> | gid:<gid> ]\n",
+			 "Usage: echo \"[dest_port=server port number] sessname=<name of the rtrs session> path=<[srcaddr@]dstaddr> [path=<[srcaddr@]dstaddr>] device_path=<full path on remote side> [access_mode=<ro|rw|migration>] [nr_poll_queues=<number of queues>]\" > %s\n\naddr ::= [ ip:<ipv4> | ip:<ipv6> | gid:<gid> ]\n",
 			 attr->attr.name);
 }
 
@@ -541,6 +571,7 @@ static ssize_t rnbd_clt_map_device_store(struct kobject *kobj,
 	char sessname[NAME_MAX];
 	enum rnbd_access_mode access_mode = RNBD_ACCESS_RW;
 	u16 port_nr = RTRS_PORT;
+	u32 nr_poll_queues = 0;
 
 	struct sockaddr_storage *addrs;
 	struct rtrs_addr paths[6];
@@ -552,6 +583,7 @@ static ssize_t rnbd_clt_map_device_store(struct kobject *kobj,
 	opt.pathname = pathname;
 	opt.dest_port = &port_nr;
 	opt.access_mode = &access_mode;
+	opt.nr_poll_queues = &nr_poll_queues;
 	addrs = kcalloc(ARRAY_SIZE(paths) * 2, sizeof(*addrs), GFP_KERNEL);
 	if (!addrs)
 		return -ENOMEM;
@@ -565,12 +597,13 @@ static ssize_t rnbd_clt_map_device_store(struct kobject *kobj,
 	if (ret)
 		goto out;
 
-	pr_info("Mapping device %s on session %s, (access_mode: %s)\n",
+	pr_info("Mapping device %s on session %s, (access_mode: %s, nr_poll_queues: %d)\n",
 		pathname, sessname,
-		rnbd_access_mode_str(access_mode));
+		rnbd_access_mode_str(access_mode),
+		nr_poll_queues);
 
 	dev = rnbd_clt_map_device(sessname, paths, path_cnt, port_nr, pathname,
-				  access_mode);
+				  access_mode, nr_poll_queues);
 	if (IS_ERR(dev)) {
 		ret = PTR_ERR(dev);
 		goto out;
diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
index 9b44aac680d5..ea98124e8ce9 100644
--- a/drivers/block/rnbd/rnbd-clt.c
+++ b/drivers/block/rnbd/rnbd-clt.c
@@ -1165,9 +1165,54 @@ static blk_status_t rnbd_queue_rq(struct blk_mq_hw_ctx *hctx,
 	return ret;
 }
 
+static int rnbd_rdma_poll(struct blk_mq_hw_ctx *hctx)
+{
+	struct rnbd_queue *q = hctx->driver_data;
+	struct rnbd_clt_dev *dev = q->dev;
+	int cnt;
+
+	cnt = rtrs_clt_rdma_cq_direct(dev->sess->rtrs, hctx->queue_num);
+	return cnt;
+}
+
+static int rnbd_rdma_map_queues(struct blk_mq_tag_set *set)
+{
+	struct rnbd_clt_session *sess = set->driver_data;
+
+	/* shared read/write queues */
+	set->map[HCTX_TYPE_DEFAULT].nr_queues = num_online_cpus();
+	set->map[HCTX_TYPE_DEFAULT].queue_offset = 0;
+	set->map[HCTX_TYPE_READ].nr_queues = num_online_cpus();
+	set->map[HCTX_TYPE_READ].queue_offset = 0;
+	blk_mq_map_queues(&set->map[HCTX_TYPE_DEFAULT]);
+	blk_mq_map_queues(&set->map[HCTX_TYPE_READ]);
+
+	if (sess->nr_poll_queues) {
+		/* dedicated queue for poll */
+		set->map[HCTX_TYPE_POLL].nr_queues = sess->nr_poll_queues;
+		set->map[HCTX_TYPE_POLL].queue_offset = set->map[HCTX_TYPE_READ].queue_offset +
+			set->map[HCTX_TYPE_READ].nr_queues;
+		blk_mq_map_queues(&set->map[HCTX_TYPE_POLL]);
+		pr_info("[session=%s] mapped %d/%d/%d default/read/poll queues.\n",
+			sess->sessname,
+			set->map[HCTX_TYPE_DEFAULT].nr_queues,
+			set->map[HCTX_TYPE_READ].nr_queues,
+			set->map[HCTX_TYPE_POLL].nr_queues);
+	} else {
+		pr_info("[session=%s] mapped %d/%d default/read queues.\n",
+			sess->sessname,
+			set->map[HCTX_TYPE_DEFAULT].nr_queues,
+			set->map[HCTX_TYPE_READ].nr_queues);
+	}
+
+	return 0;
+}
+
 static struct blk_mq_ops rnbd_mq_ops = {
 	.queue_rq	= rnbd_queue_rq,
 	.complete	= rnbd_softirq_done_fn,
+	.map_queues     = rnbd_rdma_map_queues,
+	.poll           = rnbd_rdma_poll,
 };
 
 static int setup_mq_tags(struct rnbd_clt_session *sess)
@@ -1181,7 +1226,15 @@ static int setup_mq_tags(struct rnbd_clt_session *sess)
 	tag_set->flags		= BLK_MQ_F_SHOULD_MERGE |
 				  BLK_MQ_F_TAG_QUEUE_SHARED;
 	tag_set->cmd_size	= sizeof(struct rnbd_iu) + RNBD_RDMA_SGL_SIZE;
-	tag_set->nr_hw_queues	= num_online_cpus();
+
+	/* for HCTX_TYPE_DEFAULT, HCTX_TYPE_READ, HCTX_TYPE_POLL */
+	tag_set->nr_maps        = sess->nr_poll_queues ? HCTX_MAX_TYPES : 2;
+	/*
+	 * HCTX_TYPE_DEFAULT and HCTX_TYPE_READ share one set of queues
+	 * others are for HCTX_TYPE_POLL
+	 */
+	tag_set->nr_hw_queues	= num_online_cpus() + sess->nr_poll_queues;
+	tag_set->driver_data    = sess;
 
 	return blk_mq_alloc_tag_set(tag_set);
 }
@@ -1189,7 +1242,7 @@ static int setup_mq_tags(struct rnbd_clt_session *sess)
 static struct rnbd_clt_session *
 find_and_get_or_create_sess(const char *sessname,
 			    const struct rtrs_addr *paths,
-			    size_t path_cnt, u16 port_nr)
+			    size_t path_cnt, u16 port_nr, u32 nr_poll_queues)
 {
 	struct rnbd_clt_session *sess;
 	struct rtrs_attrs attrs;
@@ -1198,6 +1251,17 @@ find_and_get_or_create_sess(const char *sessname,
 	struct rtrs_clt_ops rtrs_ops;
 
 	sess = find_or_create_sess(sessname, &first);
+	if (sess == ERR_PTR(-ENOMEM))
+		return ERR_PTR(-ENOMEM);
+	else if ((nr_poll_queues && !first) ||  (!nr_poll_queues && sess->nr_poll_queues)) {
+		/*
+		 * A device MUST have its own session to use the polling-mode.
+		 * It must fail to map new device with the same session.
+		 */
+		err = -EINVAL;
+		goto put_sess;
+	}
+
 	if (!first)
 		return sess;
 
@@ -1219,7 +1283,7 @@ find_and_get_or_create_sess(const char *sessname,
 				   0, /* Do not use pdu of rtrs */
 				   RECONNECT_DELAY, BMAX_SEGMENTS,
 				   BLK_MAX_SEGMENT_SIZE,
-				   MAX_RECONNECTS);
+				   MAX_RECONNECTS, nr_poll_queues);
 	if (IS_ERR(sess->rtrs)) {
 		err = PTR_ERR(sess->rtrs);
 		goto wake_up_and_put;
@@ -1227,6 +1291,7 @@ find_and_get_or_create_sess(const char *sessname,
 	rtrs_clt_query(sess->rtrs, &attrs);
 	sess->max_io_size = attrs.max_io_size;
 	sess->queue_depth = attrs.queue_depth;
+	sess->nr_poll_queues = nr_poll_queues;
 
 	err = setup_mq_tags(sess);
 	if (err)
@@ -1370,7 +1435,8 @@ static int rnbd_client_setup_device(struct rnbd_clt_dev *dev)
 
 static struct rnbd_clt_dev *init_dev(struct rnbd_clt_session *sess,
 				      enum rnbd_access_mode access_mode,
-				      const char *pathname)
+				      const char *pathname,
+				      u32 nr_poll_queues)
 {
 	struct rnbd_clt_dev *dev;
 	int ret;
@@ -1379,7 +1445,12 @@ static struct rnbd_clt_dev *init_dev(struct rnbd_clt_session *sess,
 	if (!dev)
 		return ERR_PTR(-ENOMEM);
 
-	dev->hw_queues = kcalloc(nr_cpu_ids, sizeof(*dev->hw_queues),
+	/*
+	 * nr_cpu_ids: the number of softirq queues
+	 * nr_poll_queues: the number of polling queues
+	 */
+	dev->hw_queues = kcalloc(nr_cpu_ids + nr_poll_queues,
+				 sizeof(*dev->hw_queues),
 				 GFP_KERNEL);
 	if (!dev->hw_queues) {
 		ret = -ENOMEM;
@@ -1405,6 +1476,7 @@ static struct rnbd_clt_dev *init_dev(struct rnbd_clt_session *sess,
 	dev->clt_device_id	= ret;
 	dev->sess		= sess;
 	dev->access_mode	= access_mode;
+	dev->nr_poll_queues	= nr_poll_queues;
 	mutex_init(&dev->lock);
 	refcount_set(&dev->refcount, 1);
 	dev->dev_state = DEV_STATE_INIT;
@@ -1491,7 +1563,8 @@ struct rnbd_clt_dev *rnbd_clt_map_device(const char *sessname,
 					   struct rtrs_addr *paths,
 					   size_t path_cnt, u16 port_nr,
 					   const char *pathname,
-					   enum rnbd_access_mode access_mode)
+					   enum rnbd_access_mode access_mode,
+					   u32 nr_poll_queues)
 {
 	struct rnbd_clt_session *sess;
 	struct rnbd_clt_dev *dev;
@@ -1500,11 +1573,11 @@ struct rnbd_clt_dev *rnbd_clt_map_device(const char *sessname,
 	if (unlikely(exists_devpath(pathname, sessname)))
 		return ERR_PTR(-EEXIST);
 
-	sess = find_and_get_or_create_sess(sessname, paths, path_cnt, port_nr);
+	sess = find_and_get_or_create_sess(sessname, paths, path_cnt, port_nr, nr_poll_queues);
 	if (IS_ERR(sess))
 		return ERR_CAST(sess);
 
-	dev = init_dev(sess, access_mode, pathname);
+	dev = init_dev(sess, access_mode, pathname, nr_poll_queues);
 	if (IS_ERR(dev)) {
 		pr_err("map_device: failed to map device '%s' from session %s, can't initialize device, err: %ld\n",
 		       pathname, sess->sessname, PTR_ERR(dev));
diff --git a/drivers/block/rnbd/rnbd-clt.h b/drivers/block/rnbd/rnbd-clt.h
index 714d426b449b..451e7383738f 100644
--- a/drivers/block/rnbd/rnbd-clt.h
+++ b/drivers/block/rnbd/rnbd-clt.h
@@ -90,6 +90,7 @@ struct rnbd_clt_session {
 	int			queue_depth;
 	u32			max_io_size;
 	struct blk_mq_tag_set	tag_set;
+	u32			nr_poll_queues;
 	struct mutex		lock; /* protects state and devs_list */
 	struct list_head        devs_list; /* list of struct rnbd_clt_dev */
 	refcount_t		refcount;
@@ -118,6 +119,7 @@ struct rnbd_clt_dev {
 	enum rnbd_clt_dev_state	dev_state;
 	char			*pathname;
 	enum rnbd_access_mode	access_mode;
+	u32			nr_poll_queues;
 	bool			read_only;
 	bool			rotational;
 	bool			wc;
@@ -147,7 +149,8 @@ struct rnbd_clt_dev *rnbd_clt_map_device(const char *sessname,
 					   struct rtrs_addr *paths,
 					   size_t path_cnt, u16 port_nr,
 					   const char *pathname,
-					   enum rnbd_access_mode access_mode);
+					   enum rnbd_access_mode access_mode,
+					   u32 nr_poll_queues);
 int rnbd_clt_unmap_device(struct rnbd_clt_dev *dev, bool force,
 			   const struct attribute *sysfs_self);