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, 1 insertions, 3 deletions

diff --git a/net/rds/ib.h b/net/rds/ib.h
index 67a715b076ca..66c03c7665b2 100644
--- a/net/rds/ib.h
+++ b/net/rds/ib.h
@@ -15,8 +15,7 @@
 
 #define RDS_IB_DEFAULT_RECV_WR		1024
 #define RDS_IB_DEFAULT_SEND_WR		256
-#define RDS_IB_DEFAULT_FR_WR		256
-#define RDS_IB_DEFAULT_FR_INV_WR	256
+#define RDS_IB_DEFAULT_FR_WR		512
 
 #define RDS_IB_DEFAULT_RETRY_COUNT	1
 
@@ -157,7 +156,6 @@ struct rds_ib_connection {
 
 	/* To control the number of wrs from fastreg */
 	atomic_t		i_fastreg_wrs;
-	atomic_t		i_fastunreg_wrs;
 
 	/* interrupt handling */
 	struct tasklet_struct	i_send_tasklet;