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

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

[Feng Yang]

From: Feng Yang <yangfeng@kylinos.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@google.com>
Signed-off-by: Feng Yang <yangfeng@kylinos.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

Re: [PATCH v4] skbuff: Add MSG_MORE flag to optimize tcp large packet transmission

[Eric Dumazet]

On Mon, Jul 7, 2025 at 10:41 PM Feng Yang <yangfeng59949@163.com> wrote:
>
> From: Feng Yang <yangfeng@kylinos.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@google.com>
> Signed-off-by: Feng Yang <yangfeng@kylinos.cn>

Reviewed-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH v4] skbuff: Add MSG_MORE flag to optimize tcp large packet transmission

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue,  8 Jul 2025 13:40:53 +0800 you wrote:
> From: Feng Yang <yangfeng@kylinos.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
> 
> [...]

Here is the summary with links:
  - [v4] skbuff: Add MSG_MORE flag to optimize tcp large packet transmission
    https://git.kernel.org/netdev/net-next/c/76d727ae02b5

You are awesome, thank you!
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