When user_frac in the polling subsystem is low it is going to busy the

CPU for too long period than necessary.  Additively, interfaces are kept
polled (in the tick) even if no more packets are available.
In order to avoid such situations a new generic mechanism can be
implemented in proactive way, keeping track of the time spent on any
packet and fragmenting the time for any tick, stopping the processing
as soon as possible.

In order to implement such mechanism, the polling handler needs to
change, returning the number of packets processed.
While the intended logic is not part of this patch, the polling KPI is
broken by this commit, adding an int return value and the new flag
IFCAP_POLLING_NOCOUNT (which will signal that the return value is
meaningless for the installed handler and checking should be skipped).

Bump __FreeBSD_version in order to signal such situation.

Reviewed by:	emaste
Sponsored by:	Sandvine Incorporated

1 files changed, 16 insertions, 9 deletions

diff --git a/sys/dev/xl/if_xl.c b/sys/dev/xl/if_xl.c
index 073aa41..a0f7042 100644
--- a/sys/dev/xl/if_xl.c
+++ b/sys/dev/xl/if_xl.c
@@ -228,7 +228,7 @@ static int xl_newbuf(struct xl_softc *, struct xl_chain_onefrag *);
 static void xl_stats_update(void *);
 static void xl_stats_update_locked(struct xl_softc *);
 static int xl_encap(struct xl_softc *, struct xl_chain *, struct mbuf **);
-static void xl_rxeof(struct xl_softc *);
+static int xl_rxeof(struct xl_softc *);
 static void xl_rxeof_task(void *, int);
 static int xl_rx_resync(struct xl_softc *);
 static void xl_txeof(struct xl_softc *);
@@ -248,8 +248,8 @@ static int xl_suspend(device_t);
 static int xl_resume(device_t);
 
 #ifdef DEVICE_POLLING
-static void xl_poll(struct ifnet *ifp, enum poll_cmd cmd, int count);
-static void xl_poll_locked(struct ifnet *ifp, enum poll_cmd cmd, int count);
+static int xl_poll(struct ifnet *ifp, enum poll_cmd cmd, int count);
+static int xl_poll_locked(struct ifnet *ifp, enum poll_cmd cmd, int count);
 #endif
 
 static int xl_ifmedia_upd(struct ifnet *);
@@ -1882,13 +1882,14 @@ xl_rx_resync(struct xl_softc *sc)
  * A frame has been uploaded: pass the resulting mbuf chain up to
  * the higher level protocols.
  */
-static void
+static int
 xl_rxeof(struct xl_softc *sc)
 {
 	struct mbuf		*m;
 	struct ifnet		*ifp = sc->xl_ifp;
 	struct xl_chain_onefrag	*cur_rx;
 	int			total_len = 0;
+	int			rx_npkts = 0;
 	u_int32_t		rxstat;
 
 	XL_LOCK_ASSERT(sc);
@@ -1990,6 +1991,7 @@ again:
 		XL_UNLOCK(sc);
 		(*ifp->if_input)(ifp, m);
 		XL_LOCK(sc);
+		rx_npkts++;
 
 		/*
 		 * If we are running from the taskqueue, the interface
@@ -1997,7 +1999,7 @@ again:
 		 * packet up the network stack.
 		 */
 		if (!(ifp->if_drv_flags & IFF_DRV_RUNNING))
-			return;
+			return (rx_npkts);
 	}
 
 	/*
@@ -2021,6 +2023,7 @@ again:
 		CSR_WRITE_2(sc, XL_COMMAND, XL_CMD_UP_UNSTALL);
 		goto again;
 	}
+	return (rx_npkts);
 }
 
 /*
@@ -2265,26 +2268,29 @@ xl_intr(void *arg)
 }
 
 #ifdef DEVICE_POLLING
-static void
+static int
 xl_poll(struct ifnet *ifp, enum poll_cmd cmd, int count)
 {
 	struct xl_softc *sc = ifp->if_softc;
+	int rx_npkts = 0;
 
 	XL_LOCK(sc);
 	if (ifp->if_drv_flags & IFF_DRV_RUNNING)
-		xl_poll_locked(ifp, cmd, count);
+		rx_npkts = xl_poll_locked(ifp, cmd, count);
 	XL_UNLOCK(sc);
+	return (rx_npkts);
 }
 
-static void
+static int
 xl_poll_locked(struct ifnet *ifp, enum poll_cmd cmd, int count)
 {
 	struct xl_softc *sc = ifp->if_softc;
+	int rx_npkts;
 
 	XL_LOCK_ASSERT(sc);
 
 	sc->rxcycles = count;
-	xl_rxeof(sc);
+	rx_npkts = xl_rxeof(sc);
 	if (sc->xl_type == XL_TYPE_905B)
 		xl_txeof_90xB(sc);
 	else
@@ -2322,6 +2328,7 @@ xl_poll_locked(struct ifnet *ifp, enum poll_cmd cmd, int count)
 			}
 		}
 	}
+	return (rx_npkts);
 }
 #endif /* DEVICE_POLLING */