netdev - [RFC net-next 04/17] net/smc: Decouple sf and attached send_buf in smc

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Message-ID: <20250806154122.3413330-5-wintera@linux.ibm.com>
Date: Wed,  6 Aug 2025 17:41:09 +0200
From: Alexandra Winter <wintera@...ux.ibm.com>
To: David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>,
        Andrew Lunn <andrew+netdev@...n.ch>,
        "D. Wythe" <alibuda@...ux.alibaba.com>,
        Dust Li <dust.li@...ux.alibaba.com>,
        Sidraya Jayagond <sidraya@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Julian Ruess <julianr@...ux.ibm.com>
Cc: netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thorsten Winkler <twinkler@...ux.ibm.com>,
        Simon Horman <horms@...nel.org>,
        Mahanta Jambigi <mjambigi@...ux.ibm.com>,
        Tony Lu <tonylu@...ux.alibaba.com>, Wen Gu <guwen@...ux.alibaba.com>,
        Halil Pasic <pasic@...ux.ibm.com>, linux-rdma@...r.kernel.org
Subject: [RFC net-next 04/17] net/smc: Decouple sf and attached send_buf in smc_loopback

Before this patch there was the following assumption in
smc_loopback.c>smc_lo_move_data():
sf (signalling flag) == 0 : data is already in an attached target dmb
sf == 1 : data is not yet in the target dmb

This is true for the 2 callers in smc client
smcd_cdc_msg_send() : sf=1
smcd_tx_rdma_writes() : sf=0
but should not be a general assumption.

Add a bool to struct smc_buf_desc to indicate whether an SMC-D sndbuf_desc
is an attached buffer. Don't call move_data() for attached send_buffers,
because it is not necessary.

Move the data in smc_lo_move_data() if len != 0 and signal when requested.

Signed-off-by: Alexandra Winter <wintera@...ux.ibm.com>
Reviewed-by: Mahanta Jambigi <mjambigi@...ux.ibm.com>
---
 net/smc/smc_core.h     | 5 +++++
 net/smc/smc_ism.c      | 1 +
 net/smc/smc_loopback.c | 9 +++------
 net/smc/smc_tx.c       | 3 +++
 4 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/net/smc/smc_core.h b/net/smc/smc_core.h
index 48a1b1dcb576..fe5f48d14323 100644
--- a/net/smc/smc_core.h
+++ b/net/smc/smc_core.h
@@ -13,6 +13,7 @@
 #define _SMC_CORE_H
 
 #include <linux/atomic.h>
+#include <linux/types.h>
 #include <linux/smc.h>
 #include <linux/pci.h>
 #include <rdma/ib_verbs.h>
@@ -221,12 +222,16 @@ struct smc_buf_desc {
 					/* virtually contiguous */
 		};
 		struct { /* SMC-D */
+			 /* SMC-D rx buffer: */
 			unsigned short	sba_idx;
 					/* SBA index number */
 			u64		token;
 					/* DMB token number */
 			dma_addr_t	dma_addr;
 					/* DMA address */
+			/* SMC-D tx buffer */
+			bool		is_attached;
+					/* no need for explicit writes */
 		};
 	};
 };
diff --git a/net/smc/smc_ism.c b/net/smc/smc_ism.c
index a94e1450d095..7363f8be9f94 100644
--- a/net/smc/smc_ism.c
+++ b/net/smc/smc_ism.c
@@ -274,6 +274,7 @@ int smc_ism_attach_dmb(struct smcd_dev *dev, u64 token,
 		dmb_desc->cpu_addr = dmb.cpu_addr;
 		dmb_desc->dma_addr = dmb.dma_addr;
 		dmb_desc->len = dmb.dmb_len;
+		dmb_desc->is_attached = true;
 	}
 	return rc;
 }
diff --git a/net/smc/smc_loopback.c b/net/smc/smc_loopback.c
index 0eb00bbefd17..1853c26fbbbb 100644
--- a/net/smc/smc_loopback.c
+++ b/net/smc/smc_loopback.c
@@ -224,12 +224,6 @@ static int smc_lo_move_data(struct smcd_dev *smcd, u64 dmb_tok,
 	struct smc_lo_dev *ldev = smcd->priv;
 	struct smc_connection *conn;
 
-	if (!sf)
-		/* since sndbuf is merged with peer DMB, there is
-		 * no need to copy data from sndbuf to peer DMB.
-		 */
-		return 0;
-
 	read_lock_bh(&ldev->dmb_ht_lock);
 	hash_for_each_possible(ldev->dmb_ht, tmp_node, list, dmb_tok) {
 		if (tmp_node->token == dmb_tok) {
@@ -244,6 +238,9 @@ static int smc_lo_move_data(struct smcd_dev *smcd, u64 dmb_tok,
 	memcpy((char *)rmb_node->cpu_addr + offset, data, size);
 	read_unlock_bh(&ldev->dmb_ht_lock);
 
+	if (!sf)
+		return 0;
+
 	conn = smcd->conn[rmb_node->sba_idx];
 	if (!conn || conn->killed)
 		return -EPIPE;
diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index 214ac3cbcf9a..3144b4b1fe29 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -426,6 +426,9 @@ static int smcd_tx_rdma_writes(struct smc_connection *conn, size_t len,
 	int srcchunk, dstchunk;
 	int rc;
 
+	if (conn->sndbuf_desc->is_attached)
+		return 0;
+
 	for (dstchunk = 0; dstchunk < 2; dstchunk++) {
 		for (srcchunk = 0; srcchunk < 2; srcchunk++) {
 			void *data = conn->sndbuf_desc->cpu_addr + src_off;
-- 
2.48.1