Revert "RDS: IB: split the mr registration and invalidation path"

This reverts commit 56012459310a1dbcc55c2dbf5500a9f7571402cb.

RDS kept spinning inside function "rds_ib_post_reg_frmr", waiting for
"i_fastreg_wrs" to become incremented:
         while (atomic_dec_return(&ibmr->ic->i_fastreg_wrs) <= 0) {
                 atomic_inc(&ibmr->ic->i_fastreg_wrs);
                 cpu_relax();
         }

Looking at the original commit:

commit 56012459310a ("RDS: IB: split the mr registration and
invalidation path")

In there, the "rds_ib_mr_cqe_handler" was changed in the following
way:

 void rds_ib_mr_cqe_handler(struct
 rds_ib_connection *ic,
 struct ib_wc *wc)
        if (frmr->fr_inv) {
                  frmr->fr_state = FRMR_IS_FREE;
                  frmr->fr_inv = false;
                atomic_inc(&ic->i_fastreg_wrs);
        } else {
                atomic_inc(&ic->i_fastunreg_wrs);
        }

It looks like it's got it exactly backwards:

Function "rds_ib_post_reg_frmr" keeps track of the outstanding
requests via "i_fastreg_wrs".

Function "rds_ib_post_inv" keeps track of the outstanding requests
via "i_fastunreg_wrs" (post original commit). It also sets:
         frmr->fr_inv = true;

However the completion handler "rds_ib_mr_cqe_handler" adjusts
"i_fastreg_wrs" when "fr_inv" had been true, and adjusts
"i_fastunreg_wrs" otherwise.

The original commit was done in the name of performance:
to remove the performance bottleneck

No performance benefit could be observed with a fixed-up version
of the original commit measured between two Oracle X7 servers,
both equipped with Mellanox Connect-X5 HCAs.

The prudent course of action is to revert this commit.

Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>

1 files changed, 2 insertions, 7 deletions

diff --git a/net/rds/ib_cm.c b/net/rds/ib_cm.c
index 66c6eb56072b..8891822eba4f 100644
--- a/net/rds/ib_cm.c
+++ b/net/rds/ib_cm.c
@@ -460,10 +460,7 @@ static int rds_ib_setup_qp(struct rds_connection *conn)
 	 * completion queue and send queue. This extra space is used for FRMR
 	 * registration and invalidation work requests
 	 */
-	fr_queue_space = rds_ibdev->use_fastreg ?
-			 (RDS_IB_DEFAULT_FR_WR + 1) +
-			 (RDS_IB_DEFAULT_FR_INV_WR + 1)
-			 : 0;
+	fr_queue_space = (rds_ibdev->use_fastreg ? RDS_IB_DEFAULT_FR_WR : 0);
 
 	/* add the conn now so that connection establishment has the dev */
 	rds_ib_add_conn(rds_ibdev, conn);
@@ -530,7 +527,6 @@ static int rds_ib_setup_qp(struct rds_connection *conn)
 	attr.send_cq = ic->i_send_cq;
 	attr.recv_cq = ic->i_recv_cq;
 	atomic_set(&ic->i_fastreg_wrs, RDS_IB_DEFAULT_FR_WR);
-	atomic_set(&ic->i_fastunreg_wrs, RDS_IB_DEFAULT_FR_INV_WR);
 
 	/*
 	 * XXX this can fail if max_*_wr is too large?  Are we supposed
@@ -1009,8 +1005,7 @@ void rds_ib_conn_path_shutdown(struct rds_conn_path *cp)
 		wait_event(rds_ib_ring_empty_wait,
 			   rds_ib_ring_empty(&ic->i_recv_ring) &&
 			   (atomic_read(&ic->i_signaled_sends) == 0) &&
-			   (atomic_read(&ic->i_fastreg_wrs) == RDS_IB_DEFAULT_FR_WR) &&
-			   (atomic_read(&ic->i_fastunreg_wrs) == RDS_IB_DEFAULT_FR_INV_WR));
+			   (atomic_read(&ic->i_fastreg_wrs) == RDS_IB_DEFAULT_FR_WR));
 		tasklet_kill(&ic->i_send_tasklet);
 		tasklet_kill(&ic->i_recv_tasklet);