First step towards parallel transmit in UDP: if neither a specific

source or a specific destination address is requested as part of a send
on a UDP socket, read lock the inpcb rather than write lock it.  This
will allow fully parallel transmit down to the IP layer when sending
simultaneously from multiple threads on a connected UDP socket.

Parallel transmit for more complex cases, such as when sendto(2) is
invoked with an address and there's already a local binding, will
follow.

MFC after:	1 month

1 files changed, 12 insertions, 5 deletions

diff --git a/sys/netinet/udp_usrreq.c b/sys/netinet/udp_usrreq.c
index f63fd0b..9422e7e 100644
--- a/sys/netinet/udp_usrreq.c
+++ b/sys/netinet/udp_usrreq.c
@@ -841,10 +841,12 @@ udp_output(struct inpcb *inp, struct mbuf *m, struct sockaddr *addr,
 
 	if (src.sin_family == AF_INET || addr != NULL) {
 		INP_INFO_WLOCK(&udbinfo);
+		INP_WLOCK(inp);
 		unlock_udbinfo = 1;
-	} else
+	} else {
 		unlock_udbinfo = 0;
-	INP_WLOCK(inp);
+		INP_RLOCK(inp);
+	}
 
 #ifdef MAC
 	mac_inpcb_create_mbuf(inp, m);
@@ -975,13 +977,18 @@ udp_output(struct inpcb *inp, struct mbuf *m, struct sockaddr *addr,
 		INP_INFO_WUNLOCK(&udbinfo);
 	error = ip_output(m, inp->inp_options, NULL, ipflags,
 	    inp->inp_moptions, inp);
-	INP_WUNLOCK(inp);
+	if (unlock_udbinfo)
+		INP_WUNLOCK(inp);
+	else
+		INP_RUNLOCK(inp);
 	return (error);
 
 release:
-	INP_WUNLOCK(inp);
-	if (unlock_udbinfo)
+	if (unlock_udbinfo) {
 		INP_INFO_WUNLOCK(&udbinfo);
+		INP_WUNLOCK(inp);
+	} else
+		INP_RUNLOCK(inp);
 	m_freem(m);
 	return (error);
 }