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Commit a5520788 authored by Gerd Rausch's avatar Gerd Rausch Committed by Santosh Shilimkar
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Revert "RDS: IB: split the mr registration and invalidation path" 



This reverts commit 56012459.

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 56012459 ("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: default avatarGerd Rausch <gerd.rausch@oracle.com>
Signed-off-by: default avatarSantosh Shilimkar <santosh.shilimkar@oracle.com>
parent 616d37a0

net/rds/ib.h

+1 −3
Original line number Diff line number Diff line
@@ -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;

net/rds/ib_cm.c

+2 −7
Original line number Diff line number Diff line
@@ -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);

net/rds/ib_frmr.c

+5 −6
Original line number Diff line number Diff line
@@ -239,8 +239,8 @@ static int rds_ib_post_inv(struct rds_ib_mr *ibmr) 
	if (frmr->fr_state != FRMR_IS_INUSE)

		goto out;



	while (atomic_dec_return(&ibmr->ic->i_fastunreg_wrs) <= 0) {

		atomic_inc(&ibmr->ic->i_fastunreg_wrs);

	while (atomic_dec_return(&ibmr->ic->i_fastreg_wrs) <= 0) {

		atomic_inc(&ibmr->ic->i_fastreg_wrs);

		cpu_relax();

	}
@@ -257,7 +257,7 @@ static int rds_ib_post_inv(struct rds_ib_mr *ibmr) 
	if (unlikely(ret)) {

		frmr->fr_state = FRMR_IS_STALE;

		frmr->fr_inv = false;

		atomic_inc(&ibmr->ic->i_fastunreg_wrs);

		atomic_inc(&ibmr->ic->i_fastreg_wrs);

		pr_err("RDS/IB: %s returned error(%d)\n", __func__, ret);

		goto out;

	}
@@ -285,10 +285,9 @@ 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);

	}



	atomic_inc(&ic->i_fastreg_wrs);

}



void rds_ib_unreg_frmr(struct list_head *list, unsigned int *nfreed,