IB/srpt: Change default behavior from using SRQ to using RC

Although in the RC mode more resources are needed that mode has three
advantages over SRQ:
- It works with all RDMA adapters, even those that do not support
  SRQ.
- Posting WRs and polling WCs does not trigger lock contention
  because only one thread at a time accesses a WR or WC queue in
  non-SRQ mode.
- The end-to-end flow control mechanism is used.

>From the IB spec:

    C9-150.2.1: For QPs that are not associated with an SRQ, each HCA
    receive queue shall generate end-to-end flow control credits. If
    a QP is associated with an SRQ, the HCA receive queue shall not
    generate end-to-end flow control credits.

Add new configfs attributes that allow to configure which mode to use
(/sys/kernel/config/target/srpt/$GUID/$GUID/attrib/use_srq). Note:
only the attribute for port 1 is relevant on multi-port adapters.
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/ulp/srpt/ib_srpt.c

@@ -295,6 +295,7 @@ static void srpt_get_ioc(struct srpt_port *sport, u32 slot,
 {
 	struct srpt_device *sdev = sport->sdev;
 	struct ib_dm_ioc_profile *iocp;
+	int send_queue_depth;
 
 	iocp = (struct ib_dm_ioc_profile *)mad->data;
 
@@ -310,6 +311,12 @@ static void srpt_get_ioc(struct srpt_port *sport, u32 slot,
 		return;
 	}
 
+	if (sdev->use_srq)
+		send_queue_depth = sdev->srq_size;
+	else
+		send_queue_depth = min(SRPT_RQ_SIZE,
+				       sdev->device->attrs.max_qp_wr);
+
 	memset(iocp, 0, sizeof(*iocp));
 	strcpy(iocp->id_string, SRPT_ID_STRING);
 	iocp->guid = cpu_to_be64(srpt_service_guid);
@@ -322,7 +329,7 @@ static void srpt_get_ioc(struct srpt_port *sport, u32 slot,
 	iocp->io_subclass = cpu_to_be16(SRP_IO_SUBCLASS);
 	iocp->protocol = cpu_to_be16(SRP_PROTOCOL);
 	iocp->protocol_version = cpu_to_be16(SRP_PROTOCOL_VERSION);
-	iocp->send_queue_depth = cpu_to_be16(sdev->srq_size);
+	iocp->send_queue_depth = cpu_to_be16(send_queue_depth);
 	iocp->rdma_read_depth = 4;
 	iocp->send_size = cpu_to_be32(srp_max_req_size);
 	iocp->rdma_size = cpu_to_be32(min(sport->port_attrib.srp_max_rdma_size,
@@ -686,6 +693,9 @@ static void srpt_free_ioctx_ring(struct srpt_ioctx **ioctx_ring,
 {
 	int i;
 
+	if (!ioctx_ring)
+		return;
+
 	for (i = 0; i < ring_size; ++i)
 		srpt_free_ioctx(sdev, ioctx_ring[i], dma_size, dir);
 	kfree(ioctx_ring);
@@ -757,7 +767,7 @@ static bool srpt_test_and_set_cmd_state(struct srpt_send_ioctx *ioctx,
 /**
  * srpt_post_recv() - Post an IB receive request.
  */
-static int srpt_post_recv(struct srpt_device *sdev,
+static int srpt_post_recv(struct srpt_device *sdev, struct srpt_rdma_ch *ch,
 			  struct srpt_recv_ioctx *ioctx)
 {
 	struct ib_sge list;
@@ -774,7 +784,10 @@ static int srpt_post_recv(struct srpt_device *sdev,
 	wr.sg_list = &list;
 	wr.num_sge = 1;
 
+	if (sdev->use_srq)
 		return ib_post_srq_recv(sdev->srq, &wr, &bad_wr);
+	else
+		return ib_post_recv(ch->qp, &wr, &bad_wr);
 }
 
 /**
@@ -1517,7 +1530,7 @@ static void srpt_handle_new_iu(struct srpt_rdma_ch *ch,
 		break;
 	}
 
-	srpt_post_recv(ch->sport->sdev, recv_ioctx);
+	srpt_post_recv(ch->sport->sdev, ch, recv_ioctx);
 	return;
 
 out_wait:
@@ -1616,7 +1629,7 @@ static int srpt_create_ch_ib(struct srpt_rdma_ch *ch)
 	struct srpt_device *sdev = sport->sdev;
 	const struct ib_device_attr *attrs = &sdev->device->attrs;
 	u32 srp_sq_size = sport->port_attrib.srp_sq_size;
-	int ret;
+	int i, ret;
 
 	WARN_ON(ch->rq_size < 1);
 
@@ -1640,7 +1653,6 @@ static int srpt_create_ch_ib(struct srpt_rdma_ch *ch)
 		= (void(*)(struct ib_event *, void*))srpt_qp_event;
 	qp_init->send_cq = ch->cq;
 	qp_init->recv_cq = ch->cq;
-	qp_init->srq = sdev->srq;
 	qp_init->sq_sig_type = IB_SIGNAL_REQ_WR;
 	qp_init->qp_type = IB_QPT_RC;
 	/*
@@ -1654,6 +1666,12 @@ static int srpt_create_ch_ib(struct srpt_rdma_ch *ch)
 	qp_init->cap.max_rdma_ctxs = srp_sq_size / 2;
 	qp_init->cap.max_send_sge = min(attrs->max_sge, SRPT_MAX_SG_PER_WQE);
 	qp_init->port_num = ch->sport->port;
+	if (sdev->use_srq) {
+		qp_init->srq = sdev->srq;
+	} else {
+		qp_init->cap.max_recv_wr = ch->rq_size;
+		qp_init->cap.max_recv_sge = qp_init->cap.max_send_sge;
+	}
 
 	ch->qp = ib_create_qp(sdev->pd, qp_init);
 	if (IS_ERR(ch->qp)) {
@@ -1669,6 +1687,10 @@ static int srpt_create_ch_ib(struct srpt_rdma_ch *ch)
 		goto err_destroy_cq;
 	}
 
+	if (!sdev->use_srq)
+		for (i = 0; i < ch->rq_size; i++)
+			srpt_post_recv(sdev, ch, ch->ioctx_recv_ring[i]);
+
 	atomic_set(&ch->sq_wr_avail, qp_init->cap.max_send_wr);
 
 	pr_debug("%s: max_cqe= %d max_sge= %d sq_size = %d cm_id= %p\n",
@@ -1818,6 +1840,10 @@ static void srpt_release_channel_work(struct work_struct *w)
 			     ch->sport->sdev, ch->rq_size,
 			     ch->rsp_size, DMA_TO_DEVICE);
 
+	srpt_free_ioctx_ring((struct srpt_ioctx **)ch->ioctx_recv_ring,
+			     sdev, ch->rq_size,
+			     srp_max_req_size, DMA_FROM_DEVICE);
+
 	mutex_lock(&sdev->mutex);
 	list_del_init(&ch->list);
 	if (ch->release_done)
@@ -1975,6 +2001,19 @@ static int srpt_cm_req_recv(struct ib_cm_id *cm_id,
 		ch->ioctx_ring[i]->ch = ch;
 		list_add_tail(&ch->ioctx_ring[i]->free_list, &ch->free_list);
 	}
+	if (!sdev->use_srq) {
+		ch->ioctx_recv_ring = (struct srpt_recv_ioctx **)
+			srpt_alloc_ioctx_ring(ch->sport->sdev, ch->rq_size,
+					      sizeof(*ch->ioctx_recv_ring[0]),
+					      srp_max_req_size,
+					      DMA_FROM_DEVICE);
+		if (!ch->ioctx_recv_ring) {
+			pr_err("rejected SRP_LOGIN_REQ because creating a new QP RQ ring failed.\n");
+			rej->reason =
+			    cpu_to_be32(SRP_LOGIN_REJ_INSUFFICIENT_RESOURCES);
+			goto free_ring;
+		}
+	}
 
 	ret = srpt_create_ch_ib(ch);
 	if (ret) {
@@ -1982,7 +2021,7 @@ static int srpt_cm_req_recv(struct ib_cm_id *cm_id,
 			      SRP_LOGIN_REJ_INSUFFICIENT_RESOURCES);
 		pr_err("rejected SRP_LOGIN_REQ because creating"
 		       " a new RDMA channel failed.\n");
-		goto free_ring;
+		goto free_recv_ring;
 	}
 
 	ret = srpt_ch_qp_rtr(ch, ch->qp);
@@ -2073,6 +2112,11 @@ static int srpt_cm_req_recv(struct ib_cm_id *cm_id,
 destroy_ib:
 	srpt_destroy_ch_ib(ch);
 
+free_recv_ring:
+	srpt_free_ioctx_ring((struct srpt_ioctx **)ch->ioctx_recv_ring,
+			     ch->sport->sdev, ch->rq_size,
+			     srp_max_req_size, DMA_FROM_DEVICE);
+
 free_ring:
 	srpt_free_ioctx_ring((struct srpt_ioctx **)ch->ioctx_ring,
 			     ch->sport->sdev, ch->rq_size,
@@ -2502,20 +2546,38 @@ static void srpt_add_one(struct ib_device *device)
 	srq_attr.attr.srq_limit = 0;
 	srq_attr.srq_type = IB_SRQT_BASIC;
 
-	sdev->srq = ib_create_srq(sdev->pd, &srq_attr);
-	if (IS_ERR(sdev->srq))
-		goto err_pd;
+	sdev->srq = sdev->port[0].port_attrib.use_srq ?
+		ib_create_srq(sdev->pd, &srq_attr) : ERR_PTR(-ENOTSUPP);
+	if (IS_ERR(sdev->srq)) {
+		pr_debug("ib_create_srq() failed: %ld\n", PTR_ERR(sdev->srq));
 
-	pr_debug("%s: create SRQ #wr= %d max_allow=%d dev= %s\n",
-		 __func__, sdev->srq_size, sdev->device->attrs.max_srq_wr,
+		/* SRQ not supported. */
+		sdev->use_srq = false;
+	} else {
+		pr_debug("create SRQ #wr= %d max_allow=%d dev= %s\n",
+			 sdev->srq_size, sdev->device->attrs.max_srq_wr,
 			 device->name);
 
+		sdev->use_srq = true;
+
+		sdev->ioctx_ring = (struct srpt_recv_ioctx **)
+			srpt_alloc_ioctx_ring(sdev, sdev->srq_size,
+					      sizeof(*sdev->ioctx_ring[0]),
+					      srp_max_req_size,
+					      DMA_FROM_DEVICE);
+		if (!sdev->ioctx_ring)
+			goto err_pd;
+
+		for (i = 0; i < sdev->srq_size; ++i)
+			srpt_post_recv(sdev, NULL, sdev->ioctx_ring[i]);
+	}
+
 	if (!srpt_service_guid)
 		srpt_service_guid = be64_to_cpu(device->node_guid);
 
 	sdev->cm_id = ib_create_cm_id(device, srpt_cm_handler, sdev);
 	if (IS_ERR(sdev->cm_id))
-		goto err_srq;
+		goto err_ring;
 
 	/* print out target login information */
 	pr_debug("Target login info: id_ext=%016llx,ioc_guid=%016llx,"
@@ -2535,16 +2597,6 @@ static void srpt_add_one(struct ib_device *device)
 			      srpt_event_handler);
 	ib_register_event_handler(&sdev->event_handler);
 
-	sdev->ioctx_ring = (struct srpt_recv_ioctx **)
-		srpt_alloc_ioctx_ring(sdev, sdev->srq_size,
-				      sizeof(*sdev->ioctx_ring[0]),
-				      srp_max_req_size, DMA_FROM_DEVICE);
-	if (!sdev->ioctx_ring)
-		goto err_event;
-
-	for (i = 0; i < sdev->srq_size; ++i)
-		srpt_post_recv(sdev, sdev->ioctx_ring[i]);
-
 	WARN_ON(sdev->device->phys_port_cnt > ARRAY_SIZE(sdev->port));
 
 	for (i = 1; i <= sdev->device->phys_port_cnt; i++) {
@@ -2554,12 +2606,13 @@ static void srpt_add_one(struct ib_device *device)
 		sport->port_attrib.srp_max_rdma_size = DEFAULT_MAX_RDMA_SIZE;
 		sport->port_attrib.srp_max_rsp_size = DEFAULT_MAX_RSP_SIZE;
 		sport->port_attrib.srp_sq_size = DEF_SRPT_SQ_SIZE;
+		sport->port_attrib.use_srq = false;
 		INIT_WORK(&sport->work, srpt_refresh_port_work);
 
 		if (srpt_refresh_port(sport)) {
 			pr_err("MAD registration failed for %s-%d.\n",
 			       sdev->device->name, i);
-			goto err_ring;
+			goto err_event;
 		}
 	}
 
@@ -2572,16 +2625,16 @@ static void srpt_add_one(struct ib_device *device)
 	pr_debug("added %s.\n", device->name);
 	return;
 
-err_ring:
-	srpt_free_ioctx_ring((struct srpt_ioctx **)sdev->ioctx_ring, sdev,
-			     sdev->srq_size, srp_max_req_size,
-			     DMA_FROM_DEVICE);
 err_event:
 	ib_unregister_event_handler(&sdev->event_handler);
 err_cm:
 	ib_destroy_cm_id(sdev->cm_id);
-err_srq:
+err_ring:
+	if (sdev->use_srq)
 		ib_destroy_srq(sdev->srq);
+	srpt_free_ioctx_ring((struct srpt_ioctx **)sdev->ioctx_ring, sdev,
+			     sdev->srq_size, srp_max_req_size,
+			     DMA_FROM_DEVICE);
 err_pd:
 	ib_dealloc_pd(sdev->pd);
 free_dev:
@@ -2625,12 +2678,12 @@ static void srpt_remove_one(struct ib_device *device, void *client_data)
 	spin_unlock(&srpt_dev_lock);
 	srpt_release_sdev(sdev);
 
+	if (sdev->use_srq)
 		ib_destroy_srq(sdev->srq);
-	ib_dealloc_pd(sdev->pd);
-
 	srpt_free_ioctx_ring((struct srpt_ioctx **)sdev->ioctx_ring, sdev,
 			     sdev->srq_size, srp_max_req_size, DMA_FROM_DEVICE);
-	sdev->ioctx_ring = NULL;
+	ib_dealloc_pd(sdev->pd);
+
 	kfree(sdev);
 }
 
@@ -2928,14 +2981,43 @@ static ssize_t srpt_tpg_attrib_srp_sq_size_store(struct config_item *item,
 	return count;
 }
 
+static ssize_t srpt_tpg_attrib_use_srq_show(struct config_item *item,
+					    char *page)
+{
+	struct se_portal_group *se_tpg = attrib_to_tpg(item);
+	struct srpt_port *sport = srpt_tpg_to_sport(se_tpg);
+
+	return sprintf(page, "%d\n", sport->port_attrib.use_srq);
+}
+
+static ssize_t srpt_tpg_attrib_use_srq_store(struct config_item *item,
+					     const char *page, size_t count)
+{
+	struct se_portal_group *se_tpg = attrib_to_tpg(item);
+	struct srpt_port *sport = srpt_tpg_to_sport(se_tpg);
+	unsigned long val;
+	int ret;
+
+	ret = kstrtoul(page, 0, &val);
+	if (ret < 0)
+		return ret;
+	if (val != !!val)
+		return -EINVAL;
+	sport->port_attrib.use_srq = val;
+
+	return count;
+}
+
 CONFIGFS_ATTR(srpt_tpg_attrib_,  srp_max_rdma_size);
 CONFIGFS_ATTR(srpt_tpg_attrib_,  srp_max_rsp_size);
 CONFIGFS_ATTR(srpt_tpg_attrib_,  srp_sq_size);
+CONFIGFS_ATTR(srpt_tpg_attrib_,  use_srq);
 
 static struct configfs_attribute *srpt_tpg_attrib_attrs[] = {
 	&srpt_tpg_attrib_attr_srp_max_rdma_size,
 	&srpt_tpg_attrib_attr_srp_max_rsp_size,
 	&srpt_tpg_attrib_attr_srp_sq_size,
+	&srpt_tpg_attrib_attr_use_srq,
 	NULL,
 };
 

drivers/infiniband/ulp/srpt/ib_srpt.h

@@ -252,6 +252,7 @@ enum rdma_ch_state {
  * @free_list:     Head of list with free send I/O contexts.
  * @state:         channel state. See also enum rdma_ch_state.
  * @ioctx_ring:    Send ring.
+ * @ioctx_recv_ring: Receive I/O context ring.
  * @list:          Node for insertion in the srpt_device.rch_list list.
  * @cmd_wait_list: List of SCSI commands that arrived before the RTU event. This
  *                 list contains struct srpt_ioctx elements and is protected
@@ -281,6 +282,7 @@ struct srpt_rdma_ch {
 	struct list_head	free_list;
 	enum rdma_ch_state	state;
 	struct srpt_send_ioctx	**ioctx_ring;
+	struct srpt_recv_ioctx	**ioctx_recv_ring;
 	struct list_head	list;
 	struct list_head	cmd_wait_list;
 	struct se_session	*sess;
@@ -295,11 +297,13 @@ struct srpt_rdma_ch {
  * @srp_max_rdma_size: Maximum size of SRP RDMA transfers for new connections.
  * @srp_max_rsp_size: Maximum size of SRP response messages in bytes.
  * @srp_sq_size: Shared receive queue (SRQ) size.
+ * @use_srq: Whether or not to use SRQ.
  */
 struct srpt_port_attrib {
 	u32			srp_max_rdma_size;
 	u32			srp_max_rsp_size;
 	u32			srp_sq_size;
+	bool			use_srq;
 };
 
 /**
@@ -347,6 +351,7 @@ struct srpt_port {
  * @srq:           Per-HCA SRQ (shared receive queue).
  * @cm_id:         Connection identifier.
  * @srq_size:      SRQ size.
+ * @use_srq:       Whether or not to use SRQ.
  * @ioctx_ring:    Per-HCA SRQ.
  * @rch_list:      Per-device channel list -- see also srpt_rdma_ch.list.
  * @ch_releaseQ:   Enables waiting for removal from rch_list.
@@ -362,6 +367,7 @@ struct srpt_device {
 	struct ib_srq		*srq;
 	struct ib_cm_id		*cm_id;
 	int			srq_size;
+	bool			use_srq;
 	struct srpt_recv_ioctx	**ioctx_ring;
 	struct list_head	rch_list;
 	wait_queue_head_t	ch_releaseQ;