skbuff: Add MSG_MORE flag to optimize tcp large packet transmission

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>
Link: https://patch.msgid.link/20250708054053.39551-1-yangfeng59949@163.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a6efabff2173ea8300ad592b2494fc3acb191aff..ee0274417948e0eb121792a400a0455884c92e56 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3230,6 +3230,7 @@ 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;
@@ -3247,6 +3248,8 @@ do_frag_list:
                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,
@@ -3287,6 +3290,8 @@ do_frag_list:
                                             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,