Remove the periodic timer and do rescheduling during Rx completion

This change adds a check into the Rx ring completion routine that
schedules an interrupt task to be executed immediately after if
consumer index has already advanced itself.  The benefit of doing
this compared to an additional loop after replenishing the ring
(as done in FreeBSD for example) is that first of all this goes
through the loop in the taskqueue thread with a yeild check to
prevent CPU hogging and second is that it triggers Tx completion
as well since interrupt handler runs both.

diff --git a/sys/dev/pv/if_xnf.c b/sys/dev/pv/if_xnf.c
index 2b5d4bf..df28b5f 100644 (file)
--- a/sys/dev/pv/if_xnf.c
+++ b/sys/dev/pv/if_xnf.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: if_xnf.c,v 1.30 2016/08/01 13:48:33 mikeb Exp $       */
+/*     $OpenBSD: if_xnf.c,v 1.31 2016/08/03 15:08:06 mikeb Exp $       */
 
 /*
  * Copyright (c) 2015, 2016 Mike Belopuhov
@@ -158,7 +158,6 @@ struct xnf_softc {
        struct ifmedia           sc_media;
 
        xen_intr_handle_t        sc_xih;
-       struct timeout           sc_timer;
 
        int                      sc_caps;
 #define  XNF_CAP_SG              0x0001
@@ -201,11 +200,10 @@ void      xnf_stop(struct xnf_softc *);
 void   xnf_start(struct ifnet *);
 int    xnf_encap(struct xnf_softc *, struct mbuf *, uint32_t *);
 void   xnf_intr(void *);
-void   xnf_timer(void *);
 void   xnf_watchdog(struct ifnet *);
-int    xnf_txeof(struct xnf_softc *);
-int    xnf_rxeof(struct xnf_softc *);
-void   xnf_rx_ring_fill(void *);
+void   xnf_txeof(struct xnf_softc *);
+void   xnf_rxeof(struct xnf_softc *);
+int    xnf_rx_ring_fill(struct xnf_softc *);
 int    xnf_rx_ring_create(struct xnf_softc *);
 void   xnf_rx_ring_drain(struct xnf_softc *);
 void   xnf_rx_ring_destroy(struct xnf_softc *);
@@ -310,8 +308,6 @@ xnf_attach(struct device *parent, struct device *self, void *aux)
        if_attach(ifp);
        ether_ifattach(ifp);
 
-       timeout_set(&sc->sc_timer, xnf_timer, sc);
-
        /* Kick out emulated em's and re's */
        sc->sc_xen->sc_flags |= XSF_UNPLUG_NIC;
 }
@@ -443,7 +439,6 @@ xnf_stop(struct xnf_softc *sc)
 
        xen_intr_mask(sc->sc_xih);
 
-       timeout_del(&sc->sc_timer);
        ifp->if_timer = 0;
 
        ifq_barrier(&ifp->if_snd);
@@ -610,22 +605,11 @@ xnf_intr(void *arg)
        struct ifnet *ifp = &sc->sc_ac.ac_if;
 
        if (ifp->if_flags & IFF_RUNNING) {
-               xnf_rxeof(sc);
                xnf_txeof(sc);
-               timeout_add(&sc->sc_timer, 10);
+               xnf_rxeof(sc);
        }
 }
 
-void
-xnf_timer(void *arg)
-{
-       struct xnf_softc *sc = arg;
-       struct ifnet *ifp = &sc->sc_ac.ac_if;
-
-       if (ifp->if_flags & IFF_RUNNING)
-               xen_intr_schedule(sc->sc_xih);
-}
-
 void
 xnf_watchdog(struct ifnet *ifp)
 {
@@ -637,7 +621,7 @@ xnf_watchdog(struct ifnet *ifp)
            txr->txr_prod_event, txr->txr_cons_event);
 }
 
-int
+void
 xnf_txeof(struct xnf_softc *sc)
 {
        struct ifnet *ifp = &sc->sc_ac.ac_if;
@@ -680,11 +664,9 @@ xnf_txeof(struct xnf_softc *sc)
                ifp->if_timer = 0;
        if (ifq_is_oactive(&ifp->if_snd))
                ifq_restart(&ifp->if_snd);
-
-       return (0);
 }
 
-int
+void
 xnf_rxeof(struct xnf_softc *sc)
 {
        struct ifnet *ifp = &sc->sc_ac.ac_if;
@@ -768,24 +750,22 @@ xnf_rxeof(struct xnf_softc *sc)
        bus_dmamap_sync(sc->sc_dmat, sc->sc_rx_rmap, 0, 0,
            BUS_DMASYNC_PREREAD | BUS_DMASYNC_PREWRITE);
 
-       xnf_rx_ring_fill(sc);
-
        if (!ml_empty(&ml))
                if_input(ifp, &ml);
 
-       return (0);
+       if (xnf_rx_ring_fill(sc) || (sc->sc_rx_cons != rxr->rxr_cons))
+               xen_intr_schedule(sc->sc_xih);
 }
 
-void
-xnf_rx_ring_fill(void *arg)
+int
+xnf_rx_ring_fill(struct xnf_softc *sc)
 {
-       struct xnf_softc *sc = arg;
        struct ifnet *ifp = &sc->sc_ac.ac_if;
        struct xnf_rx_ring *rxr = sc->sc_rx_ring;
        bus_dmamap_t dmap;
        struct mbuf *m;
        uint32_t cons, prod, oprod;
-       int i, flags;
+       int i, flags, resched = 0;
 
        cons = rxr->rxr_cons;
        prod = oprod = rxr->rxr_prod;
@@ -815,9 +795,11 @@ xnf_rx_ring_fill(void *arg)
            BUS_DMASYNC_PREREAD | BUS_DMASYNC_PREWRITE);
 
        if ((prod - cons < XNF_RX_MIN) && (ifp->if_flags & IFF_RUNNING))
-               xen_intr_schedule(sc->sc_xih);
+               resched = 1;
        if (prod - rxr->rxr_prod_event < prod - oprod)
                xen_intr_signal(sc->sc_xih);
+
+       return (resched);
 }
 
 int