Convert the if_lagg rwlock to an rmlock.

We've been seeing lots of cache line contention (but not lock contention!)
in our workloads between the various TX and RX threads going on.

The write lock is only grabbed when configuration changes are made - which
are infrequent.

With this patch, the contention and cycles spent waiting for updates
disappear.

Sponsored by:	Netflix, Inc.

2 files changed, 56 insertions, 33 deletions

diff --git a/sys/net/if_lagg.c b/sys/net/if_lagg.c
index a46e1f3..27bab87 100644
--- a/sys/net/if_lagg.c
+++ b/sys/net/if_lagg.c
@@ -37,7 +37,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/proc.h>
 #include <sys/hash.h>
 #include <sys/lock.h>
-#include <sys/rwlock.h>
+#include <sys/rmlock.h>
 #include <sys/taskqueue.h>
 #include <sys/eventhandler.h>
 
@@ -233,16 +233,17 @@ lagg_register_vlan(void *arg, struct ifnet *ifp, u_int16_t vtag)
 {
         struct lagg_softc       *sc = ifp->if_softc;
         struct lagg_port        *lp;
+        struct rm_priotracker   tracker;
 
         if (ifp->if_softc !=  arg)   /* Not our event */
                 return;
 
-        LAGG_RLOCK(sc);
+        LAGG_RLOCK(sc, &tracker);
         if (!SLIST_EMPTY(&sc->sc_ports)) {
                 SLIST_FOREACH(lp, &sc->sc_ports, lp_entries)
                         EVENTHANDLER_INVOKE(vlan_config, lp->lp_ifp, vtag);
         }
-        LAGG_RUNLOCK(sc);
+        LAGG_RUNLOCK(sc, &tracker);
 }
 
 /*
@@ -254,16 +255,17 @@ lagg_unregister_vlan(void *arg, struct ifnet *ifp, u_int16_t vtag)
 {
         struct lagg_softc       *sc = ifp->if_softc;
         struct lagg_port        *lp;
+        struct rm_priotracker   tracker;
 
         if (ifp->if_softc !=  arg)   /* Not our event */
                 return;
 
-        LAGG_RLOCK(sc);
+        LAGG_RLOCK(sc, &tracker);
         if (!SLIST_EMPTY(&sc->sc_ports)) {
                 SLIST_FOREACH(lp, &sc->sc_ports, lp_entries)
                         EVENTHANDLER_INVOKE(vlan_unconfig, lp->lp_ifp, vtag);
         }
-        LAGG_RUNLOCK(sc);
+        LAGG_RUNLOCK(sc, &tracker);
 }
 
 static int
@@ -322,9 +324,15 @@ lagg_clone_create(struct if_clone *ifc, int unit, caddr_t params)
 		}
 	}
 	LAGG_LOCK_INIT(sc);
+	LAGG_CALLOUT_LOCK_INIT(sc);
 	SLIST_INIT(&sc->sc_ports);
 	TASK_INIT(&sc->sc_lladdr_task, 0, lagg_port_setlladdr, sc);
-	callout_init_rw(&sc->sc_callout, &sc->sc_mtx, CALLOUT_SHAREDLOCK);
+
+	/*
+	 * This uses the callout lock rather than the rmlock; one can't
+	 * hold said rmlock during SWI.
+	 */
+	callout_init_mtx(&sc->sc_callout, &sc->sc_call_mtx, 0);
 
 	/* Initialise pseudo media types */
 	ifmedia_init(&sc->sc_media, 0, lagg_media_change,
@@ -389,7 +397,10 @@ lagg_clone_destroy(struct ifnet *ifp)
 	ether_ifdetach(ifp);
 	if_free(ifp);
 
+	/* This grabs sc_callout_mtx, serialising it correctly */
 	callout_drain(&sc->sc_callout);
+
+	/* At this point it's drained; we can free this */
 	counter_u64_free(sc->sc_ipackets);
 	counter_u64_free(sc->sc_opackets);
 	counter_u64_free(sc->sc_ibytes);
@@ -401,6 +412,7 @@ lagg_clone_destroy(struct ifnet *ifp)
 
 	taskqueue_drain(taskqueue_swi, &sc->sc_lladdr_task);
 	LAGG_LOCK_DESTROY(sc);
+	LAGG_CALLOUT_LOCK_DESTROY(sc);
 	free(sc, M_DEVBUF);
 }
 
@@ -764,6 +776,7 @@ lagg_port_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 	struct lagg_softc *sc;
 	struct lagg_port *lp = NULL;
 	int error = 0;
+	struct rm_priotracker tracker;
 
 	/* Should be checked by the caller */
 	if (ifp->if_type != IFT_IEEE8023ADLAG ||
@@ -778,15 +791,15 @@ lagg_port_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 			break;
 		}
 
-		LAGG_RLOCK(sc);
+		LAGG_RLOCK(sc, &tracker);
 		if ((lp = ifp->if_lagg) == NULL || lp->lp_softc != sc) {
 			error = ENOENT;
-			LAGG_RUNLOCK(sc);
+			LAGG_RUNLOCK(sc, &tracker);
 			break;
 		}
 
 		lagg_port2req(lp, rp);
-		LAGG_RUNLOCK(sc);
+		LAGG_RUNLOCK(sc, &tracker);
 		break;
 
 	case SIOCSIFCAP:
@@ -955,21 +968,22 @@ lagg_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 	struct thread *td = curthread;
 	char *buf, *outbuf;
 	int count, buflen, len, error = 0;
+	struct rm_priotracker tracker;
 
 	bzero(&rpbuf, sizeof(rpbuf));
 
 	switch (cmd) {
 	case SIOCGLAGG:
-		LAGG_RLOCK(sc);
+		LAGG_RLOCK(sc, &tracker);
 		count = 0;
 		SLIST_FOREACH(lp, &sc->sc_ports, lp_entries)
 			count++;
 		buflen = count * sizeof(struct lagg_reqport);
-		LAGG_RUNLOCK(sc);
+		LAGG_RUNLOCK(sc, &tracker);
 
 		outbuf = malloc(buflen, M_TEMP, M_WAITOK | M_ZERO);
 
-		LAGG_RLOCK(sc);
+		LAGG_RLOCK(sc, &tracker);
 		ra->ra_proto = sc->sc_proto;
 		if (sc->sc_req != NULL)
 			(*sc->sc_req)(sc, (caddr_t)&ra->ra_psc);
@@ -987,7 +1001,7 @@ lagg_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 			buf += sizeof(rpbuf);
 			len -= sizeof(rpbuf);
 		}
-		LAGG_RUNLOCK(sc);
+		LAGG_RUNLOCK(sc, &tracker);
 		ra->ra_ports = count;
 		ra->ra_size = count * sizeof(rpbuf);
 		error = copyout(outbuf, ra->ra_port, ra->ra_size);
@@ -1065,16 +1079,16 @@ lagg_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 			break;
 		}
 
-		LAGG_RLOCK(sc);
+		LAGG_RLOCK(sc, &tracker);
 		if ((lp = (struct lagg_port *)tpif->if_lagg) == NULL ||
 		    lp->lp_softc != sc) {
 			error = ENOENT;
-			LAGG_RUNLOCK(sc);
+			LAGG_RUNLOCK(sc, &tracker);
 			break;
 		}
 
 		lagg_port2req(lp, rp);
-		LAGG_RUNLOCK(sc);
+		LAGG_RUNLOCK(sc, &tracker);
 		break;
 	case SIOCSLAGGPORT:
 		error = priv_check(td, PRIV_NET_LAGG);
@@ -1280,14 +1294,15 @@ lagg_transmit(struct ifnet *ifp, struct mbuf *m)
 {
 	struct lagg_softc *sc = (struct lagg_softc *)ifp->if_softc;
 	int error, len, mcast;
+	struct rm_priotracker tracker;
 
 	len = m->m_pkthdr.len;
 	mcast = (m->m_flags & (M_MCAST | M_BCAST)) ? 1 : 0;
 
-	LAGG_RLOCK(sc);
+	LAGG_RLOCK(sc, &tracker);
 	/* We need a Tx algorithm and at least one port */
 	if (sc->sc_proto == LAGG_PROTO_NONE || sc->sc_count == 0) {
-		LAGG_RUNLOCK(sc);
+		LAGG_RUNLOCK(sc, &tracker);
 		m_freem(m);
 		ifp->if_oerrors++;
 		return (ENXIO);
@@ -1296,7 +1311,7 @@ lagg_transmit(struct ifnet *ifp, struct mbuf *m)
 	ETHER_BPF_MTAP(ifp, m);
 
 	error = (*sc->sc_start)(sc, m);
-	LAGG_RUNLOCK(sc);
+	LAGG_RUNLOCK(sc, &tracker);
 
 	if (error == 0) {
 		counter_u64_add(sc->sc_opackets, 1);
@@ -1322,12 +1337,13 @@ lagg_input(struct ifnet *ifp, struct mbuf *m)
 	struct lagg_port *lp = ifp->if_lagg;
 	struct lagg_softc *sc = lp->lp_softc;
 	struct ifnet *scifp = sc->sc_ifp;
+	struct rm_priotracker tracker;
 
-	LAGG_RLOCK(sc);
+	LAGG_RLOCK(sc, &tracker);
 	if ((scifp->if_drv_flags & IFF_DRV_RUNNING) == 0 ||
 	    (lp->lp_flags & LAGG_PORT_DISABLED) ||
 	    sc->sc_proto == LAGG_PROTO_NONE) {
-		LAGG_RUNLOCK(sc);
+		LAGG_RUNLOCK(sc, &tracker);
 		m_freem(m);
 		return (NULL);
 	}
@@ -1346,7 +1362,7 @@ lagg_input(struct ifnet *ifp, struct mbuf *m)
 		}
 	}
 
-	LAGG_RUNLOCK(sc);
+	LAGG_RUNLOCK(sc, &tracker);
 	return (m);
 }
 
@@ -1367,16 +1383,17 @@ lagg_media_status(struct ifnet *ifp, struct ifmediareq *imr)
 {
 	struct lagg_softc *sc = (struct lagg_softc *)ifp->if_softc;
 	struct lagg_port *lp;
+	struct rm_priotracker tracker;
 
 	imr->ifm_status = IFM_AVALID;
 	imr->ifm_active = IFM_ETHER | IFM_AUTO;
 
-	LAGG_RLOCK(sc);
+	LAGG_RLOCK(sc, &tracker);
 	SLIST_FOREACH(lp, &sc->sc_ports, lp_entries) {
 		if (LAGG_PORTACTIVE(lp))
 			imr->ifm_status |= IFM_ACTIVE;
 	}
-	LAGG_RUNLOCK(sc);
+	LAGG_RUNLOCK(sc, &tracker);
 }
 
 static void
diff --git a/sys/net/if_lagg.h b/sys/net/if_lagg.h
index a851f44..0db8da8 100644
--- a/sys/net/if_lagg.h
+++ b/sys/net/if_lagg.h
@@ -187,7 +187,8 @@ struct lagg_llq {
 
 struct lagg_softc {
 	struct ifnet			*sc_ifp;	/* virtual interface */
-	struct rwlock			sc_mtx;
+	struct rmlock			sc_mtx;
+	struct mtx			sc_call_mtx;
 	int				sc_proto;	/* lagg protocol */
 	u_int				sc_count;	/* number of ports */
 	u_int				sc_active;	/* active port count */
@@ -255,14 +256,19 @@ struct lagg_port {
 	SLIST_ENTRY(lagg_port)		lp_entries;
 };
 
-#define	LAGG_LOCK_INIT(_sc)	rw_init(&(_sc)->sc_mtx, "if_lagg rwlock")
-#define	LAGG_LOCK_DESTROY(_sc)	rw_destroy(&(_sc)->sc_mtx)
-#define	LAGG_RLOCK(_sc)		rw_rlock(&(_sc)->sc_mtx)
-#define	LAGG_WLOCK(_sc)		rw_wlock(&(_sc)->sc_mtx)
-#define	LAGG_RUNLOCK(_sc)	rw_runlock(&(_sc)->sc_mtx)
-#define	LAGG_WUNLOCK(_sc)	rw_wunlock(&(_sc)->sc_mtx)
-#define	LAGG_RLOCK_ASSERT(_sc)	rw_assert(&(_sc)->sc_mtx, RA_RLOCKED)
-#define	LAGG_WLOCK_ASSERT(_sc)	rw_assert(&(_sc)->sc_mtx, RA_WLOCKED)
+#define	LAGG_LOCK_INIT(_sc)	rm_init(&(_sc)->sc_mtx, "if_lagg rmlock")
+#define	LAGG_LOCK_DESTROY(_sc)	rm_destroy(&(_sc)->sc_mtx)
+#define	LAGG_RLOCK(_sc, _p)	rm_rlock(&(_sc)->sc_mtx, (_p))
+#define	LAGG_WLOCK(_sc)		rm_wlock(&(_sc)->sc_mtx)
+#define	LAGG_RUNLOCK(_sc, _p)	rm_runlock(&(_sc)->sc_mtx, (_p))
+#define	LAGG_WUNLOCK(_sc)	rm_wunlock(&(_sc)->sc_mtx)
+#define	LAGG_RLOCK_ASSERT(_sc)	rm_assert(&(_sc)->sc_mtx, RA_RLOCKED)
+#define	LAGG_WLOCK_ASSERT(_sc)	rm_assert(&(_sc)->sc_mtx, RA_WLOCKED)
+
+#define	LAGG_CALLOUT_LOCK_INIT(_sc)					\
+	    mtx_init(&(_sc)->sc_call_mtx, "if_lagg callout mutex", NULL,\
+	    MTX_DEF)
+#define	LAGG_CALLOUT_LOCK_DESTROY(_sc)	mtx_destroy(&(_sc)->sc_call_mtx)
 
 extern struct mbuf *(*lagg_input_p)(struct ifnet *, struct mbuf *);
 extern void	(*lagg_linkstate_p)(struct ifnet *, int );