rds: ib: Remove two ib_modify_qp() calls

For some HCAs, ib_modify_qp() is an expensive operation running
virtualized.

For both the active and passive side, the QP returned by the CM has the
state set to RTS, so no need for this excess RTS -> RTS transition. With
IB Core's ability to set the RNR Retry timer, we use this interface to
shave off another ib_modify_qp().

Fixes: ec16227e14 ("RDS/IB: Infiniband transport")
Link: https://lore.kernel.org/r/1617216194-12890-3-git-send-email-haakon.bugge@oracle.com
Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

net/rds/ib_cm.c

@@ -67,31 +67,6 @@ static void rds_ib_set_flow_control(struct rds_connection *conn, u32 credits)
 	}
 }
 
-/*
- * Tune RNR behavior. Without flow control, we use a rather
- * low timeout, but not the absolute minimum - this should
- * be tunable.
- *
- * We already set the RNR retry count to 7 (which is the
- * smallest infinite number :-) above.
- * If flow control is off, we want to change this back to 0
- * so that we learn quickly when our credit accounting is
- * buggy.
- *
- * Caller passes in a qp_attr pointer - don't waste stack spacv
- * by allocation this twice.
- */
-static void
-rds_ib_tune_rnr(struct rds_ib_connection *ic, struct ib_qp_attr *attr)
-{
-	int ret;
-
-	attr->min_rnr_timer = IB_RNR_TIMER_000_32;
-	ret = ib_modify_qp(ic->i_cm_id->qp, attr, IB_QP_MIN_RNR_TIMER);
-	if (ret)
-		printk(KERN_NOTICE "ib_modify_qp(IB_QP_MIN_RNR_TIMER): err=%d\n", -ret);
-}
-
 /*
  * Connection established.
  * We get here for both outgoing and incoming connection.
@@ -100,7 +75,6 @@ void rds_ib_cm_connect_complete(struct rds_connection *conn, struct rdma_cm_even
 {
 	struct rds_ib_connection *ic = conn->c_transport_data;
 	const union rds_ib_conn_priv *dp = NULL;
-	struct ib_qp_attr qp_attr;
 	__be64 ack_seq = 0;
 	__be32 credit = 0;
 	u8 major = 0;
@@ -168,14 +142,6 @@ void rds_ib_cm_connect_complete(struct rds_connection *conn, struct rdma_cm_even
 	 * the posted credit count. */
 	rds_ib_recv_refill(conn, 1, GFP_KERNEL);
 
-	/* Tune RNR behavior */
-	rds_ib_tune_rnr(ic, &qp_attr);
-
-	qp_attr.qp_state = IB_QPS_RTS;
-	err = ib_modify_qp(ic->i_cm_id->qp, &qp_attr, IB_QP_STATE);
-	if (err)
-		printk(KERN_NOTICE "ib_modify_qp(IB_QP_STATE, RTS): err=%d\n", err);
-
 	/* update ib_device with this local ipaddr */
 	err = rds_ib_update_ipaddr(ic->rds_ibdev, &conn->c_laddr);
 	if (err)
@@ -947,6 +913,7 @@ int rds_ib_cm_handle_connect(struct rdma_cm_id *cm_id,
 				  event->param.conn.responder_resources,
 				  event->param.conn.initiator_depth, isv6);
 
+	rdma_set_min_rnr_timer(cm_id, IB_RNR_TIMER_000_32);
 	/* rdma_accept() calls rdma_reject() internally if it fails */
 	if (rdma_accept(cm_id, &conn_param))
 		rds_ib_conn_error(conn, "rdma_accept failed\n");

net/rds/rdma_transport.c

@@ -87,6 +87,7 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id,
 
 	case RDMA_CM_EVENT_ADDR_RESOLVED:
 		rdma_set_service_type(cm_id, conn->c_tos);
+		rdma_set_min_rnr_timer(cm_id, IB_RNR_TIMER_000_32);
 		/* XXX do we need to clean up if this fails? */
 		ret = rdma_resolve_route(cm_id,
 					 RDS_RDMA_RESOLVE_TIMEOUT_MS);