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, 14 insertions, 7 deletions

diff --git a/sys/dev/fxp/if_fxp.c b/sys/dev/fxp/if_fxp.c
index 0bddd17..c332552 100644
--- a/sys/dev/fxp/if_fxp.c
+++ b/sys/dev/fxp/if_fxp.c
@@ -217,7 +217,7 @@ static int		fxp_resume(device_t dev);
 static void		fxp_intr(void *xsc);
 static void		fxp_rxcsum(struct fxp_softc *sc, struct ifnet *ifp,
 			    struct mbuf *m, uint16_t status, int pos);
-static void		fxp_intr_body(struct fxp_softc *sc, struct ifnet *ifp,
+static int		fxp_intr_body(struct fxp_softc *sc, struct ifnet *ifp,
 			    uint8_t statack, int count);
 static void 		fxp_init(void *xsc);
 static void 		fxp_init_body(struct fxp_softc *sc);
@@ -1619,16 +1619,17 @@ fxp_encap(struct fxp_softc *sc, struct mbuf **m_head)
 #ifdef DEVICE_POLLING
 static poll_handler_t fxp_poll;
 
-static void
+static int
 fxp_poll(struct ifnet *ifp, enum poll_cmd cmd, int count)
 {
 	struct fxp_softc *sc = ifp->if_softc;
 	uint8_t statack;
+	int rx_npkts = 0;
 
 	FXP_LOCK(sc);
 	if (!(ifp->if_drv_flags & IFF_DRV_RUNNING)) {
 		FXP_UNLOCK(sc);
-		return;
+		return (rx_npkts);
 	}
 
 	statack = FXP_SCB_STATACK_CXTNO | FXP_SCB_STATACK_CNA |
@@ -1639,7 +1640,7 @@ fxp_poll(struct ifnet *ifp, enum poll_cmd cmd, int count)
 		tmp = CSR_READ_1(sc, FXP_CSR_SCB_STATACK);
 		if (tmp == 0xff || tmp == 0) {
 			FXP_UNLOCK(sc);
-			return; /* nothing to do */
+			return (rx_npkts); /* nothing to do */
 		}
 		tmp &= ~statack;
 		/* ack what we can */
@@ -1647,8 +1648,9 @@ fxp_poll(struct ifnet *ifp, enum poll_cmd cmd, int count)
 			CSR_WRITE_1(sc, FXP_CSR_SCB_STATACK, tmp);
 		statack |= tmp;
 	}
-	fxp_intr_body(sc, ifp, statack, count);
+	rx_npkts = fxp_intr_body(sc, ifp, statack, count);
 	FXP_UNLOCK(sc);
+	return (rx_npkts);
 }
 #endif /* DEVICE_POLLING */
 
@@ -1805,7 +1807,7 @@ fxp_rxcsum(struct fxp_softc *sc, struct ifnet *ifp, struct mbuf *m,
 	m->m_pkthdr.csum_data = csum;
 }
 
-static void
+static int
 fxp_intr_body(struct fxp_softc *sc, struct ifnet *ifp, uint8_t statack,
     int count)
 {
@@ -1813,9 +1815,12 @@ fxp_intr_body(struct fxp_softc *sc, struct ifnet *ifp, uint8_t statack,
 	struct fxp_rx *rxp;
 	struct fxp_rfa *rfa;
 	int rnr = (statack & FXP_SCB_STATACK_RNR) ? 1 : 0;
+	int rx_npkts;
 	uint16_t status;
 
+	rx_npkts = 0;
 	FXP_LOCK_ASSERT(sc, MA_OWNED);
+
 	if (rnr)
 		sc->rnr++;
 #ifdef DEVICE_POLLING
@@ -1852,7 +1857,7 @@ fxp_intr_body(struct fxp_softc *sc, struct ifnet *ifp, uint8_t statack,
 	 * Just return if nothing happened on the receive side.
 	 */
 	if (!rnr && (statack & FXP_SCB_STATACK_FR) == 0)
-		return;
+		return (rx_npkts);
 
 	/*
 	 * Process receiver interrupts. If a no-resource (RNR)
@@ -1944,6 +1949,7 @@ fxp_intr_body(struct fxp_softc *sc, struct ifnet *ifp, uint8_t statack,
 			FXP_UNLOCK(sc);
 			(*ifp->if_input)(ifp, m);
 			FXP_LOCK(sc);
+			rx_npkts++;
 		} else {
 			/* Reuse RFA and loaded DMA map. */
 			ifp->if_iqdrops++;
@@ -1957,6 +1963,7 @@ fxp_intr_body(struct fxp_softc *sc, struct ifnet *ifp, uint8_t statack,
 		    sc->fxp_desc.rx_head->rx_addr);
 		fxp_scb_cmd(sc, FXP_SCB_COMMAND_RU_START);
 	}
+	return (rx_npkts);
 }
 
 /*