Hi,

In IPv4 TCP output we use the toelpitz hash as flow id.  It is
calculated in in_pcbconnect() and can be used for all connected
sockets.  Diff below adds it for UDP and TCP IPv6.

sf@ recommends doing this for vio(4) multiqueue distribution.
My tests do not show a difference in throughput.  Consistent
behavior and distributing packets makes sense anyway.

ok?

bluhm

Index: netinet/tcp_output.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/netinet/tcp_output.c,v
diff -u -p -r1.152 tcp_output.c
--- netinet/tcp_output.c	30 Jan 2025 14:40:50 -0000	1.152
+++ netinet/tcp_output.c	14 Feb 2025 19:35:46 -0000
@@ -1072,6 +1072,10 @@ send:
 #if NPF > 0
 	pf_mbuf_link_inpcb(m, tp->t_inpcb);
 #endif
+#if NSTOEPLITZ > 0
+	m->m_pkthdr.ph_flowid = tp->t_inpcb->inp_flowid;
+	SET(m->m_pkthdr.csum_flags, M_FLOWID);
+#endif
 
 	switch (tp->pf) {
 	case 0:	/*default to PF_INET*/
@@ -1089,10 +1093,6 @@ send:
 				ip->ip_tos |= IPTOS_ECN_ECT0;
 #endif
 		}
-#if NSTOEPLITZ > 0
-		m->m_pkthdr.ph_flowid = tp->t_inpcb->inp_flowid;
-		SET(m->m_pkthdr.csum_flags, M_FLOWID);
-#endif
 		error = ip_output(m, tp->t_inpcb->inp_options,
 		    &tp->t_inpcb->inp_route,
 		    (ip_mtudisc ? IP_MTUDISC : 0), NULL,
Index: netinet/udp_usrreq.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/netinet/udp_usrreq.c,v
diff -u -p -r1.332 udp_usrreq.c
--- netinet/udp_usrreq.c	12 Feb 2025 21:28:11 -0000	1.332
+++ netinet/udp_usrreq.c	14 Feb 2025 18:50:25 -0000
@@ -68,6 +68,9 @@
  * Research Laboratory (NRL).
  */
 
+#include "pf.h"
+#include "stoeplitz.h"
+
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/mbuf.h>
@@ -102,7 +105,6 @@
 #include <netinet6/ip6protosw.h>
 #endif /* INET6 */
 
-#include "pf.h"
 #if NPF > 0
 #include <net/pfvar.h>
 #endif
@@ -1081,10 +1083,15 @@ udp_output(struct inpcb *inp, struct mbu
 	/* force routing table */
 	m->m_pkthdr.ph_rtableid = inp->inp_rtableid;
 
+	if (inp->inp_socket->so_state & SS_ISCONNECTED) {
 #if NPF > 0
-	if (inp->inp_socket->so_state & SS_ISCONNECTED)
 		pf_mbuf_link_inpcb(m, inp);
 #endif
+#if NSTOEPLITZ > 0
+		m->m_pkthdr.ph_flowid = inp->inp_flowid;
+		SET(m->m_pkthdr.csum_flags, M_FLOWID);
+#endif
+	}
 
 	error = ip_output(m, inp->inp_options, &inp->inp_route,
 	    (inp->inp_socket->so_options & SO_BROADCAST), inp->inp_moptions,
Index: netinet6/udp6_output.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/netinet6/udp6_output.c,v
diff -u -p -r1.65 udp6_output.c
--- netinet6/udp6_output.c	17 Apr 2024 20:48:51 -0000	1.65
+++ netinet6/udp6_output.c	14 Feb 2025 18:50:41 -0000
@@ -60,6 +60,7 @@
  */
 
 #include "pf.h"
+#include "stoeplitz.h"
 
 #include <sys/param.h>
 #include <sys/mbuf.h>
@@ -227,10 +228,15 @@ udp6_output(struct inpcb *inp, struct mb
 	/* force routing table */
 	m->m_pkthdr.ph_rtableid = inp->inp_rtableid;
 
+	if (inp->inp_socket->so_state & SS_ISCONNECTED) {
 #if NPF > 0
-	if (inp->inp_socket->so_state & SS_ISCONNECTED)
 		pf_mbuf_link_inpcb(m, inp);
 #endif
+#if NSTOEPLITZ > 0
+		m->m_pkthdr.ph_flowid = inp->inp_flowid;
+		SET(m->m_pkthdr.csum_flags, M_FLOWID);
+#endif
+	}
 
 	error = ip6_output(m, optp, &inp->inp_route,
 	    flags, inp->inp_moptions6, &inp->inp_seclevel);