linux-kernel - [RFC PATCH net-next v5 8/9] net/smc: Modify cursor update logic when using mappable DMB

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Message-Id: <1682252271-2544-9-git-send-email-guwen@linux.alibaba.com>
Date:   Sun, 23 Apr 2023 20:17:50 +0800
From:   Wen Gu <guwen@...ux.alibaba.com>
To:     kgraul@...ux.ibm.com, wenjia@...ux.ibm.com, jaka@...ux.ibm.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com
Cc:     linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH net-next v5 8/9] net/smc: Modify cursor update logic when using mappable DMB

Since local sndbuf shares the same physical memory region with peer
RMB when using mappable DMBs, the cursor update logic needs to be
adapted.

The main concern is to ensure that the data written by local to this
memory region won't overwrite the data that has not been consumed by
the peer.

So in this scene, the fin_curs and sndbuf_space that were originally
updated when sending out CDC message are not updated until the cons_curs
update from the peer is received.

Signed-off-by: Wen Gu <guwen@...ux.alibaba.com>
---
 net/smc/smc_cdc.c | 50 +++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 39 insertions(+), 11 deletions(-)

diff --git a/net/smc/smc_cdc.c b/net/smc/smc_cdc.c
index 2f79bac..915b8e7 100644
--- a/net/smc/smc_cdc.c
+++ b/net/smc/smc_cdc.c
@@ -18,6 +18,7 @@
 #include "smc_tx.h"
 #include "smc_rx.h"
 #include "smc_close.h"
+#include "smc_ism.h"
 
 /********************************** send *************************************/
 
@@ -256,17 +257,24 @@ int smcd_cdc_msg_send(struct smc_connection *conn)
 		return rc;
 	smc_curs_copy(&conn->rx_curs_confirmed, &curs, conn);
 	conn->local_rx_ctrl.prod_flags.cons_curs_upd_req = 0;
-	/* Calculate transmitted data and increment free send buffer space */
-	diff = smc_curs_diff(conn->sndbuf_desc->len, &conn->tx_curs_fin,
-			     &conn->tx_curs_sent);
-	/* increased by confirmed number of bytes */
-	smp_mb__before_atomic();
-	atomic_add(diff, &conn->sndbuf_space);
-	/* guarantee 0 <= sndbuf_space <= sndbuf_desc->len */
-	smp_mb__after_atomic();
-	smc_curs_copy(&conn->tx_curs_fin, &conn->tx_curs_sent, conn);
+	if (!smc_ism_dmb_mappable(conn->lgr->smcd)) {
+		/* If local sndbuf has been mapped to peer RMB, then
+		 * don't update the tx_curs_fin and sndbuf_space until
+		 * peer has consumed the data in RMB.
+		 */
 
-	smc_tx_sndbuf_nonfull(smc);
+		/* Calculate transmitted data and increment free send buffer space */
+		diff = smc_curs_diff(conn->sndbuf_desc->len, &conn->tx_curs_fin,
+				     &conn->tx_curs_sent);
+		/* increased by confirmed number of bytes */
+		smp_mb__before_atomic();
+		atomic_add(diff, &conn->sndbuf_space);
+		/* guarantee 0 <= sndbuf_space <= sndbuf_desc->len */
+		smp_mb__after_atomic();
+		smc_curs_copy(&conn->tx_curs_fin, &conn->tx_curs_sent, conn);
+
+		smc_tx_sndbuf_nonfull(smc);
+	}
 	return rc;
 }
 
@@ -324,7 +332,7 @@ static void smc_cdc_msg_recv_action(struct smc_sock *smc,
 {
 	union smc_host_cursor cons_old, prod_old;
 	struct smc_connection *conn = &smc->conn;
-	int diff_cons, diff_prod;
+	int diff_cons, diff_prod, diff_tx;
 
 	smc_curs_copy(&prod_old, &conn->local_rx_ctrl.prod, conn);
 	smc_curs_copy(&cons_old, &conn->local_rx_ctrl.cons, conn);
@@ -340,6 +348,26 @@ static void smc_cdc_msg_recv_action(struct smc_sock *smc,
 		atomic_add(diff_cons, &conn->peer_rmbe_space);
 		/* guarantee 0 <= peer_rmbe_space <= peer_rmbe_size */
 		smp_mb__after_atomic();
+
+		if (conn->lgr->is_smcd &&
+		    smc_ism_dmb_mappable(conn->lgr->smcd)) {
+			/* If local sndbuf has been mapped to peer RMB, then
+			 * update tx_curs_fin and sndbuf_space when peer has
+			 * consumed the data in it's RMB.
+			 */
+
+			/* calculate peer rmb consumed data */
+			diff_tx = smc_curs_diff(conn->sndbuf_desc->len, &conn->tx_curs_fin,
+						&conn->local_rx_ctrl.cons);
+			/* increase local sndbuf space and fin_curs */
+			smp_mb__before_atomic();
+			atomic_add(diff_tx, &conn->sndbuf_space);
+			/* guarantee 0 <= sndbuf_space <= sndbuf_desc->len */
+			smp_mb__after_atomic();
+			smc_curs_copy(&conn->tx_curs_fin, &conn->local_rx_ctrl.cons, conn);
+
+			smc_tx_sndbuf_nonfull(smc);
+		}
 	}
 
 	diff_prod = smc_curs_diff(conn->rmb_desc->len, &prod_old,
-- 
1.8.3.1