linux-kernel - [PATCH v4] skbuff: Add MSG_MORE flag to optimize tcp large packet transmission

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Message-Id: <20250708054053.39551-1-yangfeng59949@163.com>
Date: Tue,  8 Jul 2025 13:40:53 +0800
From: Feng Yang <yangfeng59949@....com>
To: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	willemb@...gle.com,
	almasrymina@...gle.com,
	kerneljasonxing@...il.com,
	ebiggers@...gle.com,
	asml.silence@...il.com,
	aleksander.lobakin@...el.com,
	stfomichev@...il.com,
	david.laight.linux@...il.com
Cc: yangfeng@...inos.cn,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v4] skbuff: Add MSG_MORE flag to optimize tcp large packet transmission

From: Feng Yang <yangfeng@...inos.cn>

When using sockmap for forwarding, the average latency for different packet sizes
after sending 10,000 packets is as follows:
size    old(us)         new(us)
512     56              55
1472    58              58
1600    106             81
3000    145             105
5000    182             125

Suggested-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Feng Yang <yangfeng@...inos.cn>
---
Changes in v4:
- limiting MSG_MORE hint to TCP. Thanks: Paolo Abeni, David Laight, Eric Dumazet.
- Link to v3: https://lore.kernel.org/all/20250630071029.76482-1-yangfeng59949@163.com/

Changes in v3:
- Use Msg_MORE flag. Thanks: Eric Dumazet, David Laight.
- Link to v2: https://lore.kernel.org/all/20250627094406.100919-1-yangfeng59949@163.com/

Changes in v2:
- Delete dynamic memory allocation, thanks: Paolo Abeni,Stanislav Fomichev.
- Link to v1: https://lore.kernel.org/all/20250623084212.122284-1-yangfeng59949@163.com/
---
 net/core/skbuff.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 85fc82f72d26..b8da621f1552 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3235,6 +3235,7 @@ typedef int (*sendmsg_func)(struct sock *sk, struct msghdr *msg);
 static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
 			   int len, sendmsg_func sendmsg, int flags)
 {
+	int more_hint = sk_is_tcp(sk) ? MSG_MORE : 0;
 	unsigned int orig_len = len;
 	struct sk_buff *head = skb;
 	unsigned short fragidx;
@@ -3252,6 +3253,8 @@ static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
 		kv.iov_len = slen;
 		memset(&msg, 0, sizeof(msg));
 		msg.msg_flags = MSG_DONTWAIT | flags;
+		if (slen < len)
+			msg.msg_flags |= more_hint;
 
 		iov_iter_kvec(&msg.msg_iter, ITER_SOURCE, &kv, 1, slen);
 		ret = INDIRECT_CALL_2(sendmsg, sendmsg_locked,
@@ -3292,6 +3295,8 @@ static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
 					     flags,
 			};
 
+			if (slen < len)
+				msg.msg_flags |= more_hint;
 			bvec_set_page(&bvec, skb_frag_page(frag), slen,
 				      skb_frag_off(frag) + offset);
 			iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1,
-- 
2.43.0