RDMA/core: Optimize XRC target lookup

Replace the mutex with read write semaphore and use xarray instead of
linked list for XRC target QPs. This will give faster XRC target
lookup. In addition, when QP is closed, don't insert it back to the xarray
if the destroy command failed.

Link: https://lore.kernel.org/r/20200706122716.647338-4-leon@kernel.orgSigned-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/core/verbs.c

@@ -1090,13 +1090,6 @@ static void __ib_shared_qp_event_handler(struct ib_event *event, void *context)
 	spin_unlock_irqrestore(&qp->device->qp_open_list_lock, flags);
 }
 
-static void __ib_insert_xrcd_qp(struct ib_xrcd *xrcd, struct ib_qp *qp)
-{
-	mutex_lock(&xrcd->tgt_qp_mutex);
-	list_add(&qp->xrcd_list, &xrcd->tgt_qp_list);
-	mutex_unlock(&xrcd->tgt_qp_mutex);
-}
-
 static struct ib_qp *__ib_open_qp(struct ib_qp *real_qp,
 				  void (*event_handler)(struct ib_event *, void *),
 				  void *qp_context)
@@ -1139,16 +1132,15 @@ struct ib_qp *ib_open_qp(struct ib_xrcd *xrcd,
 	if (qp_open_attr->qp_type != IB_QPT_XRC_TGT)
 		return ERR_PTR(-EINVAL);
 
-	qp = ERR_PTR(-EINVAL);
-	mutex_lock(&xrcd->tgt_qp_mutex);
-	list_for_each_entry(real_qp, &xrcd->tgt_qp_list, xrcd_list) {
-		if (real_qp->qp_num == qp_open_attr->qp_num) {
-			qp = __ib_open_qp(real_qp, qp_open_attr->event_handler,
-					  qp_open_attr->qp_context);
-			break;
-		}
+	down_read(&xrcd->tgt_qps_rwsem);
+	real_qp = xa_load(&xrcd->tgt_qps, qp_open_attr->qp_num);
+	if (!real_qp) {
+		up_read(&xrcd->tgt_qps_rwsem);
+		return ERR_PTR(-EINVAL);
 	}
-	mutex_unlock(&xrcd->tgt_qp_mutex);
+	qp = __ib_open_qp(real_qp, qp_open_attr->event_handler,
+			  qp_open_attr->qp_context);
+	up_read(&xrcd->tgt_qps_rwsem);
 	return qp;
 }
 EXPORT_SYMBOL(ib_open_qp);
@@ -1157,6 +1149,7 @@ static struct ib_qp *create_xrc_qp_user(struct ib_qp *qp,
 					struct ib_qp_init_attr *qp_init_attr)
 {
 	struct ib_qp *real_qp = qp;
+	int err;
 
 	qp->event_handler = __ib_shared_qp_event_handler;
 	qp->qp_context = qp;
@@ -1172,7 +1165,12 @@ static struct ib_qp *create_xrc_qp_user(struct ib_qp *qp,
 	if (IS_ERR(qp))
 		return qp;
 
-	__ib_insert_xrcd_qp(qp_init_attr->xrcd, real_qp);
+	err = xa_err(xa_store(&qp_init_attr->xrcd->tgt_qps, real_qp->qp_num,
+			      real_qp, GFP_KERNEL));
+	if (err) {
+		ib_close_qp(qp);
+		return ERR_PTR(err);
+	}
 	return qp;
 }
 
@@ -1887,21 +1885,18 @@ static int __ib_destroy_shared_qp(struct ib_qp *qp)
 
 	real_qp = qp->real_qp;
 	xrcd = real_qp->xrcd;
-
-	mutex_lock(&xrcd->tgt_qp_mutex);
+	down_write(&xrcd->tgt_qps_rwsem);
 	ib_close_qp(qp);
 	if (atomic_read(&real_qp->usecnt) == 0)
-		list_del(&real_qp->xrcd_list);
+		xa_erase(&xrcd->tgt_qps, real_qp->qp_num);
 	else
 		real_qp = NULL;
-	mutex_unlock(&xrcd->tgt_qp_mutex);
+	up_write(&xrcd->tgt_qps_rwsem);
 
 	if (real_qp) {
 		ret = ib_destroy_qp(real_qp);
 		if (!ret)
 			atomic_dec(&xrcd->usecnt);
-		else
-			__ib_insert_xrcd_qp(xrcd, real_qp);
 	}
 
 	return 0;
@@ -2307,8 +2302,8 @@ struct ib_xrcd *ib_alloc_xrcd_user(struct ib_device *device,
 		xrcd->device = device;
 		xrcd->inode = inode;
 		atomic_set(&xrcd->usecnt, 0);
-		mutex_init(&xrcd->tgt_qp_mutex);
-		INIT_LIST_HEAD(&xrcd->tgt_qp_list);
+		init_rwsem(&xrcd->tgt_qps_rwsem);
+		xa_init(&xrcd->tgt_qps);
 	}
 
 	return xrcd;
@@ -2322,20 +2317,10 @@ EXPORT_SYMBOL(ib_alloc_xrcd_user);
  */
 int ib_dealloc_xrcd_user(struct ib_xrcd *xrcd, struct ib_udata *udata)
 {
-	struct ib_qp *qp;
-	int ret;
-
 	if (atomic_read(&xrcd->usecnt))
 		return -EBUSY;
 
-	while (!list_empty(&xrcd->tgt_qp_list)) {
-		qp = list_entry(xrcd->tgt_qp_list.next, struct ib_qp, xrcd_list);
-		ret = ib_destroy_qp(qp);
-		if (ret)
-			return ret;
-	}
-	mutex_destroy(&xrcd->tgt_qp_mutex);
-
+	WARN_ON(!xa_empty(&xrcd->tgt_qps));
 	return xrcd->device->ops.dealloc_xrcd(xrcd, udata);
 }
 EXPORT_SYMBOL(ib_dealloc_xrcd_user);

include/rdma/ib_verbs.h

@@ -1567,9 +1567,8 @@ struct ib_xrcd {
 	struct ib_device       *device;
 	atomic_t		usecnt; /* count all exposed resources */
 	struct inode	       *inode;
-
-	struct mutex		tgt_qp_mutex;
-	struct list_head	tgt_qp_list;
+	struct rw_semaphore	tgt_qps_rwsem;
+	struct xarray		tgt_qps;
 };
 
 struct ib_ah {