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Date:      Wed, 18 Nov 2020 14:55:49 +0000 (UTC)
From:      Andrew Gallatin <gallatin@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r367797 - head/sys/net
Message-ID:  <202011181455.0AIEtnuV022417@repo.freebsd.org>
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Author: gallatin
Date: Wed Nov 18 14:55:49 2020
New Revision: 367797
URL: https://svnweb.freebsd.org/changeset/base/367797

Log:
  LACP: When suppressing distributing, return ENOBUFS
  
  When links come and go, lacp goes into a "suppress distributing" mode
  where it drops traffic for 3 seconds. When in this mode, lagg/lacp
  historiclally drops traffic with ENETDOWN. That return value causes TCP
  to close any connection where it gets that value back from the lower
  parts of the stack.  This means that any TCP connection with active
  traffic during a 3-second windown when an LACP link comes or goes
  would get closed.
  
  TCP treats return values of ENOBUFS as transient errors, and re-schedules
  transmission later. So rather than returning ENETDOWN, lets
  return ENOBUFS instead.  This allows TCP connections to be preserved.
  
  I've tested this by repeatedly bouncing links on a Netlfix CDN server
  under a moderate (20Gb/s) load and overved ENOBUFS reported back to
  the TCP stack (as reported by a RACK TCP sysctl).
  
  Reviewed by:	jhb, jtl, rrs
  Sponsored by:	Netflix
  Differential Revision:	https://reviews.freebsd.org/D27188

Modified:
  head/sys/net/ieee8023ad_lacp.c
  head/sys/net/ieee8023ad_lacp.h
  head/sys/net/if_lagg.c

Modified: head/sys/net/ieee8023ad_lacp.c
==============================================================================
--- head/sys/net/ieee8023ad_lacp.c	Wed Nov 18 14:54:55 2020	(r367796)
+++ head/sys/net/ieee8023ad_lacp.c	Wed Nov 18 14:55:49 2020	(r367797)
@@ -832,7 +832,8 @@ lacp_stop(struct lagg_softc *sc)
 }
 
 struct lagg_port *
-lacp_select_tx_port_by_hash(struct lagg_softc *sc, uint32_t hash, uint8_t numa_domain)
+lacp_select_tx_port_by_hash(struct lagg_softc *sc, uint32_t hash,
+    uint8_t numa_domain, int *err)
 {
 	struct lacp_softc *lsc = LACP_SOFTC(sc);
 	struct lacp_portmap *pm;
@@ -842,12 +843,14 @@ lacp_select_tx_port_by_hash(struct lagg_softc *sc, uin
 
 	if (__predict_false(lsc->lsc_suppress_distributing)) {
 		LACP_DPRINTF((NULL, "%s: waiting transit\n", __func__));
+		*err = ENOBUFS;
 		return (NULL);
 	}
 
 	pm = &lsc->lsc_pmap[lsc->lsc_activemap];
 	if (pm->pm_count == 0) {
 		LACP_DPRINTF((NULL, "%s: no active aggregator\n", __func__));
+		*err = ENETDOWN;
 		return (NULL);
 	}
 
@@ -879,7 +882,7 @@ lacp_select_tx_port_by_hash(struct lagg_softc *sc, uin
 }
 
 struct lagg_port *
-lacp_select_tx_port(struct lagg_softc *sc, struct mbuf *m)
+lacp_select_tx_port(struct lagg_softc *sc, struct mbuf *m, int *err)
 {
 	struct lacp_softc *lsc = LACP_SOFTC(sc);
 	uint32_t hash;
@@ -892,7 +895,7 @@ lacp_select_tx_port(struct lagg_softc *sc, struct mbuf
 		hash = m_ether_tcpip_hash(sc->sc_flags, m, lsc->lsc_hashkey);
 
 	numa_domain = m->m_pkthdr.numa_domain;
-	return (lacp_select_tx_port_by_hash(sc, hash, numa_domain));
+	return (lacp_select_tx_port_by_hash(sc, hash, numa_domain, err));
 }
 
 /*

Modified: head/sys/net/ieee8023ad_lacp.h
==============================================================================
--- head/sys/net/ieee8023ad_lacp.h	Wed Nov 18 14:54:55 2020	(r367796)
+++ head/sys/net/ieee8023ad_lacp.h	Wed Nov 18 14:55:49 2020	(r367797)
@@ -292,8 +292,10 @@ struct lacp_softc {
 #define LACP_LOCK_ASSERT(_lsc)		mtx_assert(&(_lsc)->lsc_mtx, MA_OWNED)
 
 struct mbuf	*lacp_input(struct lagg_port *, struct mbuf *);
-struct lagg_port *lacp_select_tx_port(struct lagg_softc *, struct mbuf *);
-struct lagg_port *lacp_select_tx_port_by_hash(struct lagg_softc *, uint32_t, uint8_t);
+struct lagg_port *lacp_select_tx_port(struct lagg_softc *, struct mbuf *,
+    int *);
+struct lagg_port *lacp_select_tx_port_by_hash(struct lagg_softc *, uint32_t,
+    uint8_t, int *);
 void		lacp_attach(struct lagg_softc *);
 void		lacp_detach(void *);
 void		lacp_init(struct lagg_softc *);

Modified: head/sys/net/if_lagg.c
==============================================================================
--- head/sys/net/if_lagg.c	Wed Nov 18 14:54:55 2020	(r367796)
+++ head/sys/net/if_lagg.c	Wed Nov 18 14:55:49 2020	(r367797)
@@ -1763,6 +1763,7 @@ lookup_snd_tag_port(struct ifnet *ifp, uint32_t flowid
 	struct lagg_port *lp;
 	struct lagg_lb *lb;
 	uint32_t hash, p;
+	int err;
 
 	sc = ifp->if_softc;
 
@@ -1783,7 +1784,7 @@ lookup_snd_tag_port(struct ifnet *ifp, uint32_t flowid
 		    flowtype == M_HASHTYPE_NONE)
 			return (NULL);
 		hash = flowid >> sc->flowid_shift;
-		return (lacp_select_tx_port_by_hash(sc, hash, numa_domain));
+		return (lacp_select_tx_port_by_hash(sc, hash, numa_domain, &err));
 	default:
 		return (NULL);
 	}
@@ -2580,12 +2581,13 @@ static int
 lagg_lacp_start(struct lagg_softc *sc, struct mbuf *m)
 {
 	struct lagg_port *lp;
+	int err;
 
-	lp = lacp_select_tx_port(sc, m);
+	lp = lacp_select_tx_port(sc, m, &err);
 	if (lp == NULL) {
 		if_inc_counter(sc->sc_ifp, IFCOUNTER_OERRORS, 1);
 		m_freem(m);
-		return (ENETDOWN);
+		return (err);
 	}
 
 	/* Send mbuf */

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