RDMA/cxgb4: DB Drop Recovery for RDMA and LLD queues

Add module option db_fc_threshold which is the count of active QPs
that trigger automatic db flow control mode.  Automatically transition
to/from flow control mode when the active qp count crosses
db_fc_theshold.

Add more db debugfs stats

On DB DROP event from the LLD, recover all the iwarp queues.

Signed-off-by: Vipul Pandya <vipul@chelsio.com>
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/cxgb4/qp.c

@@ -42,6 +42,11 @@ static int ocqp_support = 1;
 module_param(ocqp_support, int, 0644);
 MODULE_PARM_DESC(ocqp_support, "Support on-chip SQs (default=1)");
 
+int db_fc_threshold = 2000;
+module_param(db_fc_threshold, int, 0644);
+MODULE_PARM_DESC(db_fc_threshold, "QP count/threshold that triggers automatic "
+		 "db flow control mode (default = 2000)");
+
 static void set_state(struct c4iw_qp *qhp, enum c4iw_qp_state state)
 {
 	unsigned long flag;
@@ -1143,13 +1148,19 @@ static int ring_kernel_db(struct c4iw_qp *qhp, u32 qid, u16 inc)
 
 	mutex_lock(&qhp->rhp->db_mutex);
 	do {
-		if (cxgb4_dbfifo_count(qhp->rhp->rdev.lldi.ports[0], 1) < 768) {
+
+		/*
+		 * The interrupt threshold is dbfifo_int_thresh << 6. So
+		 * make sure we don't cross that and generate an interrupt.
+		 */
+		if (cxgb4_dbfifo_count(qhp->rhp->rdev.lldi.ports[0], 1) <
+		    (qhp->rhp->rdev.lldi.dbfifo_int_thresh << 5)) {
 			writel(V_QID(qid) | V_PIDX(inc), qhp->wq.db);
 			break;
 		}
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		schedule_timeout(usecs_to_jiffies(delay));
-		delay = min(delay << 1, 200000);
+		delay = min(delay << 1, 2000);
 	} while (1);
 	mutex_unlock(&qhp->rhp->db_mutex);
 	return 0;
@@ -1388,6 +1399,14 @@ out:
 	return ret;
 }
 
+static int enable_qp_db(int id, void *p, void *data)
+{
+	struct c4iw_qp *qp = p;
+
+	t4_enable_wq_db(&qp->wq);
+	return 0;
+}
+
 int c4iw_destroy_qp(struct ib_qp *ib_qp)
 {
 	struct c4iw_dev *rhp;
@@ -1405,7 +1424,16 @@ int c4iw_destroy_qp(struct ib_qp *ib_qp)
 		c4iw_modify_qp(rhp, qhp, C4IW_QP_ATTR_NEXT_STATE, &attrs, 0);
 	wait_event(qhp->wait, !qhp->ep);
 
-	remove_handle(rhp, &rhp->qpidr, qhp->wq.sq.qid);
+	spin_lock_irq(&rhp->lock);
+	remove_handle_nolock(rhp, &rhp->qpidr, qhp->wq.sq.qid);
+	rhp->qpcnt--;
+	BUG_ON(rhp->qpcnt < 0);
+	if (rhp->qpcnt <= db_fc_threshold && rhp->db_state == FLOW_CONTROL) {
+		rhp->rdev.stats.db_state_transitions++;
+		rhp->db_state = NORMAL;
+		idr_for_each(&rhp->qpidr, enable_qp_db, NULL);
+	}
+	spin_unlock_irq(&rhp->lock);
 	atomic_dec(&qhp->refcnt);
 	wait_event(qhp->wait, !atomic_read(&qhp->refcnt));
 
@@ -1419,6 +1447,14 @@ int c4iw_destroy_qp(struct ib_qp *ib_qp)
 	return 0;
 }
 
+static int disable_qp_db(int id, void *p, void *data)
+{
+	struct c4iw_qp *qp = p;
+
+	t4_disable_wq_db(&qp->wq);
+	return 0;
+}
+
 struct ib_qp *c4iw_create_qp(struct ib_pd *pd, struct ib_qp_init_attr *attrs,
 			     struct ib_udata *udata)
 {
@@ -1508,6 +1544,11 @@ struct ib_qp *c4iw_create_qp(struct ib_pd *pd, struct ib_qp_init_attr *attrs,
 	spin_lock_irq(&rhp->lock);
 	if (rhp->db_state != NORMAL)
 		t4_disable_wq_db(&qhp->wq);
+	if (++rhp->qpcnt > db_fc_threshold && rhp->db_state == NORMAL) {
+		rhp->rdev.stats.db_state_transitions++;
+		rhp->db_state = FLOW_CONTROL;
+		idr_for_each(&rhp->qpidr, disable_qp_db, NULL);
+	}
 	ret = insert_handle_nolock(rhp, &rhp->qpidr, qhp, qhp->wq.sq.qid);
 	spin_unlock_irq(&rhp->lock);
 	if (ret)