From: Alexander Bluhm <alexander.bluhm@gmx.net>
Subject: UDP send in parallel
To: tech@openbsd.org
Date: Fri, 5 Jan 2024 23:06:16 +0100

Hi,

Sending UDP packets via datagram socket is MP safe now.  Same applies
to raw IPv4 and IPv6, and divert sockets.  Switch sosend() from
exclusive net lock to shared net lock in combination with per socket
lock.  TCP and GRE still use exclusive net lock.

Please test this diff if you have applications that run multithreaded
and send lots of UDP packets.

ok?

bluhm

Index: kern/uipc_socket.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/kern/uipc_socket.c,v
diff -u -p -r1.312 uipc_socket.c
--- kern/uipc_socket.c	19 Dec 2023 21:34:22 -0000	1.312
+++ kern/uipc_socket.c	3 Jan 2024 21:34:53 -0000
@@ -582,7 +582,7 @@ sosend(struct socket *so, struct mbuf *a
 
 #define	snderr(errno)	{ error = errno; goto release; }
 
-	solock(so);
+	solock_shared(so);
 restart:
 	if ((error = sblock(so, &so->so_snd, SBLOCKWAIT(flags))) != 0)
 		goto out;
@@ -635,9 +635,9 @@ restart:
 				if (flags & MSG_EOR)
 					top->m_flags |= M_EOR;
 			} else {
-				sounlock(so);
+				sounlock_shared(so);
 				error = m_getuio(&top, atomic, space, uio);
-				solock(so);
+				solock_shared(so);
 				if (error)
 					goto release;
 				space -= top->m_pkthdr.len;
@@ -665,7 +665,7 @@ release:
 	so->so_snd.sb_state &= ~SS_ISSENDING;
 	sbunlock(so, &so->so_snd);
 out:
-	sounlock(so);
+	sounlock_shared(so);
 	m_freem(top);
 	m_freem(control);
 	return (error);