IB/srp: Add multichannel support

Improve performance by using multiple RDMA/RC channels per SCSI
host for communication with an SRP target. About the
implementation:
- Introduce a loop over all channels in the code that uses
  target->ch.
- Set the SRP_MULTICHAN_MULTI flag during login for the creation
  of the second and subsequent channels.
- RDMA completion vectors are chosen such that RDMA completion
  interrupts are handled by the CPU socket that submitted the I/O
  request. As one can see in this patch it has been assumed if a
  system contains n CPU sockets and m RDMA completion vectors
  have been assigned to an RDMA HCA that IRQ affinity has been
  configured such that completion vectors [i*m/n..(i+1)*m/n) are
  bound to CPU socket i with 0 <= i < n.
- Modify srp_free_ch_ib() and srp_free_req_data() such that it
  becomes safe to invoke these functions after the corresponding
  allocation function failed.
- Add a ch_count sysfs attribute per target port.
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Reviewed-by: NSagi Grimberg <sagig@mellanox.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

Documentation/ABI/stable/sysfs-driver-ib_srp

@@ -55,12 +55,12 @@ Description:	Interface for making ib_srp connect to a new target.
 		  only safe with partial memory descriptor list support enabled
 		  (allow_ext_sg=1).
 		* comp_vector, a number in the range 0..n-1 specifying the
-		  MSI-X completion vector. Some HCA's allocate multiple (n)
-		  MSI-X vectors per HCA port. If the IRQ affinity masks of
-		  these interrupts have been configured such that each MSI-X
-		  interrupt is handled by a different CPU then the comp_vector
-		  parameter can be used to spread the SRP completion workload
-		  over multiple CPU's.
+		  MSI-X completion vector of the first RDMA channel. Some
+		  HCA's allocate multiple (n) MSI-X vectors per HCA port. If
+		  the IRQ affinity masks of these interrupts have been
+		  configured such that each MSI-X interrupt is handled by a
+		  different CPU then the comp_vector parameter can be used to
+		  spread the SRP completion workload over multiple CPU's.
 		* tl_retry_count, a number in the range 2..7 specifying the
 		  IB RC retry count.
 		* queue_size, the maximum number of commands that the
@@ -88,6 +88,13 @@ Description:	Whether ib_srp is allowed to include a partial memory
 		descriptor list in an SRP_CMD when communicating with an SRP
 		target.
 
+What:		/sys/class/scsi_host/host<n>/ch_count
+Date:		April 1, 2015
+KernelVersion:	3.19
+Contact:	linux-rdma@vger.kernel.org
+Description:	Number of RDMA channels used for communication with the SRP
+		target.
+
 What:		/sys/class/scsi_host/host<n>/cmd_sg_entries
 Date:		May 19, 2011
 KernelVersion:	2.6.39
@@ -95,6 +102,12 @@ Contact:	linux-rdma@vger.kernel.org
 Description:	Maximum number of data buffer descriptors that may be sent to
 		the target in a single SRP_CMD request.
 
+What:		/sys/class/scsi_host/host<n>/comp_vector
+Date:		September 2, 2013
+KernelVersion:	3.11
+Contact:	linux-rdma@vger.kernel.org
+Description:	Completion vector used for the first RDMA channel.
+
 What:		/sys/class/scsi_host/host<n>/dgid
 Date:		June 17, 2006
 KernelVersion:	2.6.17

drivers/infiniband/ulp/srp/ib_srp.c

@@ -123,6 +123,11 @@ MODULE_PARM_DESC(dev_loss_tmo,
 		 " if fast_io_fail_tmo has not been set. \"off\" means that"
 		 " this functionality is disabled.");
 
+static unsigned ch_count;
+module_param(ch_count, uint, 0444);
+MODULE_PARM_DESC(ch_count,
+		 "Number of RDMA channels to use for communication with an SRP target. Using more than one channel improves performance if the HCA supports multiple completion vectors. The default value is the minimum of four times the number of online CPU sockets and the number of completion vectors supported by the HCA.");
+
 static void srp_add_one(struct ib_device *device);
 static void srp_remove_one(struct ib_device *device);
 static void srp_recv_completion(struct ib_cq *cq, void *ch_ptr);
@@ -562,11 +567,18 @@ static void srp_free_ch_ib(struct srp_target_port *target,
 	struct srp_device *dev = target->srp_host->srp_dev;
 	int i;
 
+	if (!ch->target)
+		return;
+
 	if (ch->cm_id) {
 		ib_destroy_cm_id(ch->cm_id);
 		ch->cm_id = NULL;
 	}
 
+	/* If srp_new_cm_id() succeeded but srp_create_ch_ib() not, return. */
+	if (!ch->qp)
+		return;
+
 	if (dev->use_fast_reg) {
 		if (ch->fr_pool)
 			srp_destroy_fr_pool(ch->fr_pool);
@@ -578,6 +590,14 @@ static void srp_free_ch_ib(struct srp_target_port *target,
 	ib_destroy_cq(ch->send_cq);
 	ib_destroy_cq(ch->recv_cq);
 
+	/*
+	 * Avoid that the SCSI error handler tries to use this channel after
+	 * it has been freed. The SCSI error handler can namely continue
+	 * trying to perform recovery actions after scsi_remove_host()
+	 * returned.
+	 */
+	ch->target = NULL;
+
 	ch->qp = NULL;
 	ch->send_cq = ch->recv_cq = NULL;
 
@@ -647,7 +667,7 @@ static int srp_lookup_path(struct srp_rdma_ch *ch)
 	return ch->status;
 }
 
-static int srp_send_req(struct srp_rdma_ch *ch)
+static int srp_send_req(struct srp_rdma_ch *ch, bool multich)
 {
 	struct srp_target_port *target = ch->target;
 	struct {
@@ -688,6 +708,8 @@ static int srp_send_req(struct srp_rdma_ch *ch)
 	req->priv.req_it_iu_len = cpu_to_be32(target->max_iu_len);
 	req->priv.req_buf_fmt 	= cpu_to_be16(SRP_BUF_FORMAT_DIRECT |
 					      SRP_BUF_FORMAT_INDIRECT);
+	req->priv.req_flags	= (multich ? SRP_MULTICHAN_MULTI :
+				   SRP_MULTICHAN_SINGLE);
 	/*
 	 * In the published SRP specification (draft rev. 16a), the
 	 * port identifier format is 8 bytes of ID extension followed
@@ -769,16 +791,20 @@ static bool srp_change_conn_state(struct srp_target_port *target,
 
 static void srp_disconnect_target(struct srp_target_port *target)
 {
-	struct srp_rdma_ch *ch = &target->ch;
+	struct srp_rdma_ch *ch;
+	int i;
 
 	if (srp_change_conn_state(target, false)) {
 		/* XXX should send SRP_I_LOGOUT request */
 
-		if (ib_send_cm_dreq(ch->cm_id, NULL, 0)) {
+		for (i = 0; i < target->ch_count; i++) {
+			ch = &target->ch[i];
+			if (ch->cm_id && ib_send_cm_dreq(ch->cm_id, NULL, 0)) {
 				shost_printk(KERN_DEBUG, target->scsi_host,
 					     PFX "Sending CM DREQ failed\n");
 			}
 		}
+	}
 }
 
 static void srp_free_req_data(struct srp_target_port *target,
@@ -789,7 +815,7 @@ static void srp_free_req_data(struct srp_target_port *target,
 	struct srp_request *req;
 	int i;
 
-	if (!ch->req_ring)
+	if (!ch->target || !ch->req_ring)
 		return;
 
 	for (i = 0; i < target->req_ring_size; ++i) {
@@ -875,7 +901,8 @@ static void srp_del_scsi_host_attr(struct Scsi_Host *shost)
 
 static void srp_remove_target(struct srp_target_port *target)
 {
-	struct srp_rdma_ch *ch = &target->ch;
+	struct srp_rdma_ch *ch;
+	int i;
 
 	WARN_ON_ONCE(target->state != SRP_TARGET_REMOVED);
 
@@ -885,10 +912,18 @@ static void srp_remove_target(struct srp_target_port *target)
 	scsi_remove_host(target->scsi_host);
 	srp_stop_rport_timers(target->rport);
 	srp_disconnect_target(target);
+	for (i = 0; i < target->ch_count; i++) {
+		ch = &target->ch[i];
 		srp_free_ch_ib(target, ch);
+	}
 	cancel_work_sync(&target->tl_err_work);
 	srp_rport_put(target->rport);
+	for (i = 0; i < target->ch_count; i++) {
+		ch = &target->ch[i];
 		srp_free_req_data(target, ch);
+	}
+	kfree(target->ch);
+	target->ch = NULL;
 
 	spin_lock(&target->srp_host->target_lock);
 	list_del(&target->list);
@@ -914,12 +949,12 @@ static void srp_rport_delete(struct srp_rport *rport)
 	srp_queue_remove_work(target);
 }
 
-static int srp_connect_ch(struct srp_rdma_ch *ch)
+static int srp_connect_ch(struct srp_rdma_ch *ch, bool multich)
 {
 	struct srp_target_port *target = ch->target;
 	int ret;
 
-	WARN_ON_ONCE(target->connected);
+	WARN_ON_ONCE(!multich && target->connected);
 
 	target->qp_in_error = false;
 
@@ -929,7 +964,7 @@ static int srp_connect_ch(struct srp_rdma_ch *ch)
 
 	while (1) {
 		init_completion(&ch->done);
-		ret = srp_send_req(ch);
+		ret = srp_send_req(ch, multich);
 		if (ret)
 			return ret;
 		ret = wait_for_completion_interruptible(&ch->done);
@@ -1090,10 +1125,10 @@ static void srp_finish_req(struct srp_rdma_ch *ch, struct srp_request *req,
 static void srp_terminate_io(struct srp_rport *rport)
 {
 	struct srp_target_port *target = rport->lld_data;
-	struct srp_rdma_ch *ch = &target->ch;
+	struct srp_rdma_ch *ch;
 	struct Scsi_Host *shost = target->scsi_host;
 	struct scsi_device *sdev;
-	int i;
+	int i, j;
 
 	/*
 	 * Invoking srp_terminate_io() while srp_queuecommand() is running
@@ -1102,10 +1137,15 @@ static void srp_terminate_io(struct srp_rport *rport)
 	shost_for_each_device(sdev, shost)
 		WARN_ON_ONCE(sdev->request_queue->request_fn_active);
 
-	for (i = 0; i < target->req_ring_size; ++i) {
-		struct srp_request *req = &ch->req_ring[i];
+	for (i = 0; i < target->ch_count; i++) {
+		ch = &target->ch[i];
+
+		for (j = 0; j < target->req_ring_size; ++j) {
+			struct srp_request *req = &ch->req_ring[j];
 
-		srp_finish_req(ch, req, NULL, DID_TRANSPORT_FAILFAST << 16);
+			srp_finish_req(ch, req, NULL,
+				       DID_TRANSPORT_FAILFAST << 16);
+		}
 	}
 }
 
@@ -1121,8 +1161,9 @@ static void srp_terminate_io(struct srp_rport *rport)
 static int srp_rport_reconnect(struct srp_rport *rport)
 {
 	struct srp_target_port *target = rport->lld_data;
-	struct srp_rdma_ch *ch = &target->ch;
-	int i, ret;
+	struct srp_rdma_ch *ch;
+	int i, j, ret = 0;
+	bool multich = false;
 
 	srp_disconnect_target(target);
 
@@ -1134,27 +1175,47 @@ static int srp_rport_reconnect(struct srp_rport *rport)
 	 * case things are really fouled up. Doing so also ensures that all CM
 	 * callbacks will have finished before a new QP is allocated.
 	 */
-	ret = srp_new_cm_id(ch);
-
-	for (i = 0; i < target->req_ring_size; ++i) {
-		struct srp_request *req = &ch->req_ring[i];
+	for (i = 0; i < target->ch_count; i++) {
+		ch = &target->ch[i];
+		if (!ch->target)
+			break;
+		ret += srp_new_cm_id(ch);
+	}
+	for (i = 0; i < target->ch_count; i++) {
+		ch = &target->ch[i];
+		if (!ch->target)
+			break;
+		for (j = 0; j < target->req_ring_size; ++j) {
+			struct srp_request *req = &ch->req_ring[j];
 
 			srp_finish_req(ch, req, NULL, DID_RESET << 16);
 		}
-
+	}
+	for (i = 0; i < target->ch_count; i++) {
+		ch = &target->ch[i];
+		if (!ch->target)
+			break;
 		/*
 		 * Whether or not creating a new CM ID succeeded, create a new
-	 * QP. This guarantees that all callback functions for the old QP have
-	 * finished before any send requests are posted on the new QP.
+		 * QP. This guarantees that all completion callback function
+		 * invocations have finished before request resetting starts.
 		 */
 		ret += srp_create_ch_ib(ch);
 
 		INIT_LIST_HEAD(&ch->free_tx);
-	for (i = 0; i < target->queue_size; ++i)
-		list_add(&ch->tx_ring[i]->list, &ch->free_tx);
-
-	if (ret == 0)
-		ret = srp_connect_ch(ch);
+		for (j = 0; j < target->queue_size; ++j)
+			list_add(&ch->tx_ring[j]->list, &ch->free_tx);
+	}
+	for (i = 0; i < target->ch_count; i++) {
+		ch = &target->ch[i];
+		if (ret || !ch->target) {
+			if (i > 1)
+				ret = 0;
+			break;
+		}
+		ret = srp_connect_ch(ch, multich);
+		multich = true;
+	}
 
 	if (ret == 0)
 		shost_printk(KERN_INFO, target->scsi_host,
@@ -1650,8 +1711,8 @@ static void srp_process_rsp(struct srp_rdma_ch *ch, struct srp_rsp *rsp)
 		}
 		if (!scmnd) {
 			shost_printk(KERN_ERR, target->scsi_host,
-				     "Null scmnd for RSP w/tag %016llx\n",
-				     (unsigned long long) rsp->tag);
+				     "Null scmnd for RSP w/tag %#016llx received on ch %td / QP %#x\n",
+				     rsp->tag, ch - target->ch, ch->qp->qp_num);
 
 			spin_lock_irqsave(&ch->lock, flags);
 			ch->req_lim += be32_to_cpu(rsp->req_lim_delta);
@@ -1907,7 +1968,7 @@ static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd)
 
 	WARN_ON_ONCE(scmnd->request->tag < 0);
 	tag = blk_mq_unique_tag(scmnd->request);
-	ch = &target->ch;
+	ch = &target->ch[blk_mq_unique_tag_to_hwq(tag)];
 	idx = blk_mq_unique_tag_to_tag(tag);
 	WARN_ONCE(idx >= target->req_ring_size, "%s: tag %#x: idx %d >= %d\n",
 		  dev_name(&shost->shost_gendev), tag, idx,
@@ -2387,15 +2448,23 @@ static int srp_abort(struct scsi_cmnd *scmnd)
 	struct srp_target_port *target = host_to_target(scmnd->device->host);
 	struct srp_request *req = (struct srp_request *) scmnd->host_scribble;
 	u32 tag;
+	u16 ch_idx;
 	struct srp_rdma_ch *ch;
 	int ret;
 
 	shost_printk(KERN_ERR, target->scsi_host, "SRP abort called\n");
 
-	ch = &target->ch;
-	if (!req || !srp_claim_req(ch, req, NULL, scmnd))
+	if (!req)
 		return SUCCESS;
 	tag = blk_mq_unique_tag(scmnd->request);
+	ch_idx = blk_mq_unique_tag_to_hwq(tag);
+	if (WARN_ON_ONCE(ch_idx >= target->ch_count))
+		return SUCCESS;
+	ch = &target->ch[ch_idx];
+	if (!srp_claim_req(ch, req, NULL, scmnd))
+		return SUCCESS;
+	shost_printk(KERN_ERR, target->scsi_host,
+		     "Sending SRP abort for tag %#x\n", tag);
 	if (srp_send_tsk_mgmt(ch, tag, scmnd->device->lun,
 			      SRP_TSK_ABORT_TASK) == 0)
 		ret = SUCCESS;
@@ -2413,22 +2482,26 @@ static int srp_abort(struct scsi_cmnd *scmnd)
 static int srp_reset_device(struct scsi_cmnd *scmnd)
 {
 	struct srp_target_port *target = host_to_target(scmnd->device->host);
-	struct srp_rdma_ch *ch = &target->ch;
+	struct srp_rdma_ch *ch;
 	int i;
 
 	shost_printk(KERN_ERR, target->scsi_host, "SRP reset_device called\n");
 
+	ch = &target->ch[0];
 	if (srp_send_tsk_mgmt(ch, SRP_TAG_NO_REQ, scmnd->device->lun,
 			      SRP_TSK_LUN_RESET))
 		return FAILED;
 	if (ch->tsk_mgmt_status)
 		return FAILED;
 
+	for (i = 0; i < target->ch_count; i++) {
+		ch = &target->ch[i];
 		for (i = 0; i < target->req_ring_size; ++i) {
 			struct srp_request *req = &ch->req_ring[i];
 
 			srp_finish_req(ch, req, scmnd->device, DID_RESET << 16);
 		}
+	}
 
 	return SUCCESS;
 }
@@ -2504,7 +2577,7 @@ static ssize_t show_dgid(struct device *dev, struct device_attribute *attr,
 			 char *buf)
 {
 	struct srp_target_port *target = host_to_target(class_to_shost(dev));
-	struct srp_rdma_ch *ch = &target->ch;
+	struct srp_rdma_ch *ch = &target->ch[0];
 
 	return sprintf(buf, "%pI6\n", ch->path.dgid.raw);
 }
@@ -2521,8 +2594,14 @@ static ssize_t show_req_lim(struct device *dev,
 			    struct device_attribute *attr, char *buf)
 {
 	struct srp_target_port *target = host_to_target(class_to_shost(dev));
+	struct srp_rdma_ch *ch;
+	int i, req_lim = INT_MAX;
 
-	return sprintf(buf, "%d\n", target->ch.req_lim);
+	for (i = 0; i < target->ch_count; i++) {
+		ch = &target->ch[i];
+		req_lim = min(req_lim, ch->req_lim);
+	}
+	return sprintf(buf, "%d\n", req_lim);
 }
 
 static ssize_t show_zero_req_lim(struct device *dev,
@@ -2549,6 +2628,14 @@ static ssize_t show_local_ib_device(struct device *dev,
 	return sprintf(buf, "%s\n", target->srp_host->srp_dev->dev->name);
 }
 
+static ssize_t show_ch_count(struct device *dev, struct device_attribute *attr,
+			     char *buf)
+{
+	struct srp_target_port *target = host_to_target(class_to_shost(dev));
+
+	return sprintf(buf, "%d\n", target->ch_count);
+}
+
 static ssize_t show_comp_vector(struct device *dev,
 				struct device_attribute *attr, char *buf)
 {
@@ -2592,6 +2679,7 @@ static DEVICE_ATTR(req_lim,         S_IRUGO, show_req_lim,         NULL);
 static DEVICE_ATTR(zero_req_lim,    S_IRUGO, show_zero_req_lim,	   NULL);
 static DEVICE_ATTR(local_ib_port,   S_IRUGO, show_local_ib_port,   NULL);
 static DEVICE_ATTR(local_ib_device, S_IRUGO, show_local_ib_device, NULL);
+static DEVICE_ATTR(ch_count,        S_IRUGO, show_ch_count,        NULL);
 static DEVICE_ATTR(comp_vector,     S_IRUGO, show_comp_vector,     NULL);
 static DEVICE_ATTR(tl_retry_count,  S_IRUGO, show_tl_retry_count,  NULL);
 static DEVICE_ATTR(cmd_sg_entries,  S_IRUGO, show_cmd_sg_entries,  NULL);
@@ -2609,6 +2697,7 @@ static struct device_attribute *srp_host_attrs[] = {
 	&dev_attr_zero_req_lim,
 	&dev_attr_local_ib_port,
 	&dev_attr_local_ib_device,
+	&dev_attr_ch_count,
 	&dev_attr_comp_vector,
 	&dev_attr_tl_retry_count,
 	&dev_attr_cmd_sg_entries,
@@ -3018,7 +3107,8 @@ static ssize_t srp_create_target(struct device *dev,
 	struct srp_rdma_ch *ch;
 	struct srp_device *srp_dev = host->srp_dev;
 	struct ib_device *ibdev = srp_dev->dev;
-	int ret;
+	int ret, node_idx, node, cpu, i;
+	bool multich = false;
 
 	target_host = scsi_host_alloc(&srp_template,
 				      sizeof (struct srp_target_port));
@@ -3088,34 +3178,82 @@ static ssize_t srp_create_target(struct device *dev,
 	INIT_WORK(&target->tl_err_work, srp_tl_err_work);
 	INIT_WORK(&target->remove_work, srp_remove_work);
 	spin_lock_init(&target->lock);
-	ch = &target->ch;
+	ret = ib_query_gid(ibdev, host->port, 0, &target->sgid);
+	if (ret)
+		goto err;
+
+	ret = -ENOMEM;
+	target->ch_count = max_t(unsigned, num_online_nodes(),
+				 min(ch_count ? :
+				     min(4 * num_online_nodes(),
+					 ibdev->num_comp_vectors),
+				     num_online_cpus()));
+	target->ch = kcalloc(target->ch_count, sizeof(*target->ch),
+			     GFP_KERNEL);
+	if (!target->ch)
+		goto err;
+
+	node_idx = 0;
+	for_each_online_node(node) {
+		const int ch_start = (node_idx * target->ch_count /
+				      num_online_nodes());
+		const int ch_end = ((node_idx + 1) * target->ch_count /
+				    num_online_nodes());
+		const int cv_start = (node_idx * ibdev->num_comp_vectors /
+				      num_online_nodes() + target->comp_vector)
+				     % ibdev->num_comp_vectors;
+		const int cv_end = ((node_idx + 1) * ibdev->num_comp_vectors /
+				    num_online_nodes() + target->comp_vector)
+				   % ibdev->num_comp_vectors;
+		int cpu_idx = 0;
+
+		for_each_online_cpu(cpu) {
+			if (cpu_to_node(cpu) != node)
+				continue;
+			if (ch_start + cpu_idx >= ch_end)
+				continue;
+			ch = &target->ch[ch_start + cpu_idx];
 			ch->target = target;
-	ch->comp_vector = target->comp_vector;
+			ch->comp_vector = cv_start == cv_end ? cv_start :
+				cv_start + cpu_idx % (cv_end - cv_start);
 			spin_lock_init(&ch->lock);
 			INIT_LIST_HEAD(&ch->free_tx);
-	ret = srp_alloc_req_data(ch);
-	if (ret)
-		goto err_free_mem;
-
-	ret = ib_query_gid(ibdev, host->port, 0, &target->sgid);
+			ret = srp_new_cm_id(ch);
 			if (ret)
-		goto err_free_mem;
+				goto err_disconnect;
 
 			ret = srp_create_ch_ib(ch);
 			if (ret)
-		goto err_free_mem;
+				goto err_disconnect;
 
-	ret = srp_new_cm_id(ch);
+			ret = srp_alloc_req_data(ch);
 			if (ret)
-		goto err_free_ib;
+				goto err_disconnect;
 
-	ret = srp_connect_ch(ch);
+			ret = srp_connect_ch(ch, multich);
 			if (ret) {
 				shost_printk(KERN_ERR, target->scsi_host,
-			     PFX "Connection failed\n");
-		goto err_free_ib;
+					     PFX "Connection %d/%d failed\n",
+					     ch_start + cpu_idx,
+					     target->ch_count);
+				if (node_idx == 0 && cpu_idx == 0) {
+					goto err_disconnect;
+				} else {
+					srp_free_ch_ib(target, ch);
+					srp_free_req_data(target, ch);
+					target->ch_count = ch - target->ch;
+					break;
+				}
 			}
 
+			multich = true;
+			cpu_idx++;
+		}
+		node_idx++;
+	}
+
+	target->scsi_host->nr_hw_queues = target->ch_count;
+
 	ret = srp_add_target(host, target);
 	if (ret)
 		goto err_disconnect;
@@ -3142,11 +3280,13 @@ static ssize_t srp_create_target(struct device *dev,
 err_disconnect:
 	srp_disconnect_target(target);
 
-err_free_ib:
+	for (i = 0; i < target->ch_count; i++) {
+		ch = &target->ch[i];
 		srp_free_ch_ib(target, ch);
-
-err_free_mem:
 		srp_free_req_data(target, ch);
+	}
+
+	kfree(target->ch);
 
 err:
 	scsi_host_put(target_host);

drivers/infiniband/ulp/srp/ib_srp.h

@@ -179,8 +179,9 @@ struct srp_target_port {
 	/* read and written in the hot path */
 	spinlock_t		lock;
 
-	struct srp_rdma_ch	ch;
 	/* read only in the hot path */
+	struct srp_rdma_ch	*ch;
+	u32			ch_count;
 	u32			lkey;
 	u32			rkey;
 	enum srp_target_state	state;