Implement RX interrupt moderation using one-shot timer interrupt.

Unlike TX interrupt, ST201 does not provide any mechanism to
suppress RX interrupts. ste(4) can generate more than 70k RX
interrupts under heavy RX traffics such that these excessive
interrupts make system useless to process other useful things.
Maybe this was the major reason why polling support code was
introduced to ste(4).
The STE_COUNTDOWN register provides a programmable counter that
will generate an interrupt upon its expiration. We program
STE_DMACTL register to use 3.2us clock rate to drive the counter
register. Whenever ste(4) serves RX interrupt, the driver rearm
the timer to expire after STE_IM_RX_TIMER_DEFAULT time and disables
further generation of RX interrupts. This trick seems to work well
and ste(4) generates less than 8k RX interrupts even under 64 bytes
UDP torture test. Combined with TX interrupts, the total number of
interrupts are less than 10k which looks reasonable on heavily
loaded controller.

The default RX interrupt moderation time is 150us. Users can change
the value at any time with dev.ste.%d.int_rx_mod sysctl node.
Setting it 0 effectively disables the RX interrupt moderation
feature. Now we have both TX/RX interrupt moderation code so remove
loop of interrupt handler which resulted in sub-optimal performance
as well as more register accesses.

1 files changed, 63 insertions, 26 deletions

diff --git a/sys/dev/ste/if_ste.c b/sys/dev/ste/if_ste.c
index 8c8b121..cda287e 100644
--- a/sys/dev/ste/if_ste.c
+++ b/sys/dev/ste/if_ste.c
@@ -659,7 +659,7 @@ ste_intr(void *xsc)
 {
 	struct ste_softc *sc;
 	struct ifnet *ifp;
-	uint16_t status;
+	uint16_t intrs, status;
 
 	sc = xsc;
 	STE_LOCK(sc);
@@ -671,43 +671,67 @@ ste_intr(void *xsc)
 		return;
 	}
 #endif
-
-	/* See if this is really our interrupt. */
-	if (!(CSR_READ_2(sc, STE_ISR) & STE_ISR_INTLATCH)) {
+	/* Reading STE_ISR_ACK clears STE_IMR register. */
+	status = CSR_READ_2(sc, STE_ISR_ACK);
+	if ((ifp->if_drv_flags & IFF_DRV_RUNNING) == 0) {
 		STE_UNLOCK(sc);
 		return;
 	}
 
-	for (;;) {
-		status = CSR_READ_2(sc, STE_ISR_ACK);
+	intrs = STE_INTRS;
+	if (status == 0xFFFF || (status & intrs) == 0)
+		goto done;
 
-		if (!(status & STE_INTRS))
-			break;
-
-		if (status & STE_ISR_RX_DMADONE)
-			ste_rxeof(sc, -1);
+	if (sc->ste_int_rx_act > 0) {
+		status &= ~STE_ISR_RX_DMADONE;
+		intrs &= ~STE_IMR_RX_DMADONE;
+	}
 
-		if (status & STE_ISR_TX_DMADONE)
+	if ((status & (STE_ISR_SOFTINTR | STE_ISR_RX_DMADONE)) != 0) {
+		ste_rxeof(sc, -1);
+		/*
+		 * The controller has no ability to Rx interrupt
+		 * moderation feature. Receiving 64 bytes frames
+		 * from wire generates too many interrupts which in
+		 * turn make system useless to process other useful
+		 * things. Fortunately ST201 supports single shot
+		 * timer so use the timer to implement Rx interrupt
+		 * moderation in driver. This adds more register
+		 * access but it greatly reduces number of Rx
+		 * interrupts under high network load.
+		 */
+		if ((ifp->if_drv_flags & IFF_DRV_RUNNING) != 0 &&
+		    (sc->ste_int_rx_mod != 0)) {
+			if ((status & STE_ISR_RX_DMADONE) != 0) {
+				CSR_WRITE_2(sc, STE_COUNTDOWN,
+				    STE_TIMER_USECS(sc->ste_int_rx_mod));
+				intrs &= ~STE_IMR_RX_DMADONE;
+				sc->ste_int_rx_act = 1;
+			} else {
+				intrs |= STE_IMR_RX_DMADONE;
+				sc->ste_int_rx_act = 0;
+			}
+		}
+	}
+	if ((ifp->if_drv_flags & IFF_DRV_RUNNING) != 0) {
+		if ((status & STE_ISR_TX_DMADONE) != 0)
 			ste_txeof(sc);
-
-		if (status & STE_ISR_TX_DONE)
+		if ((status & STE_ISR_TX_DONE) != 0)
 			ste_txeoc(sc);
-
-		if (status & STE_ISR_STATS_OFLOW)
+		if ((status & STE_ISR_STATS_OFLOW) != 0)
 			ste_stats_update(sc);
-
-		if (status & STE_ISR_HOSTERR) {
-			ste_init_locked(sc);
+		if ((status & STE_ISR_HOSTERR) != 0) {
 			ifp->if_drv_flags &= ~IFF_DRV_RUNNING;
+			ste_init_locked(sc);
+			STE_UNLOCK(sc);
+			return;
 		}
+		if (!IFQ_DRV_IS_EMPTY(&ifp->if_snd))
+			ste_start_locked(ifp);
+done:
+		/* Re-enable interrupts */
+		CSR_WRITE_2(sc, STE_IMR, intrs);
 	}
-
-	/* Re-enable interrupts */
-	CSR_WRITE_2(sc, STE_IMR, STE_INTRS);
-
-	if (!IFQ_DRV_IS_EMPTY(&ifp->if_snd))
-		ste_start_locked(ifp);
-
 	STE_UNLOCK(sc);
 }
 
@@ -1538,6 +1562,7 @@ ste_init_rx_list(struct ste_softc *sc)
 	struct ste_list_data *ld;
 	int error, i;
 
+	sc->ste_int_rx_act = 0;
 	cd = &sc->ste_cdata;
 	ld = &sc->ste_ldata;
 	bzero(ld->ste_rx_list, STE_RX_LIST_SZ);
@@ -1684,6 +1709,9 @@ ste_init_locked(struct ste_softc *sc)
 	STE_SETBIT4(sc, STE_DMACTL, STE_DMACTL_TXDMA_UNSTALL);
 	STE_SETBIT4(sc, STE_DMACTL, STE_DMACTL_TXDMA_UNSTALL);
 	ste_wait(sc);
+	/* Select 3.2us timer. */
+	STE_CLRBIT4(sc, STE_DMACTL, STE_DMACTL_COUNTDOWN_SPEED |
+	    STE_DMACTL_COUNTDOWN_MODE);
 
 	/* Enable receiver and transmitter */
 	CSR_WRITE_2(sc, STE_MACCTL0, 0);
@@ -1696,6 +1724,7 @@ ste_init_locked(struct ste_softc *sc)
 	/* Clear stats counters. */
 	ste_stats_clear(sc);
 
+	CSR_WRITE_2(sc, STE_COUNTDOWN, 0);
 	CSR_WRITE_2(sc, STE_ISR, 0xFFFF);
 #ifdef DEVICE_POLLING
 	/* Disable interrupts if we are polling. */
@@ -1733,6 +1762,7 @@ ste_stop(struct ste_softc *sc)
 	ifp->if_drv_flags &= ~(IFF_DRV_RUNNING|IFF_DRV_OACTIVE);
 
 	CSR_WRITE_2(sc, STE_IMR, 0);
+	CSR_WRITE_2(sc, STE_COUNTDOWN, 0);
 	/* Stop pending DMA. */
 	val = CSR_READ_4(sc, STE_DMACTL);
 	val |= STE_DMACTL_TXDMA_STALL | STE_DMACTL_RXDMA_STALL;
@@ -2105,6 +2135,13 @@ ste_sysctl_node(struct ste_softc *sc)
 	ctx = device_get_sysctl_ctx(sc->ste_dev);
 	child = SYSCTL_CHILDREN(device_get_sysctl_tree(sc->ste_dev));
 
+	SYSCTL_ADD_INT(ctx, child, OID_AUTO, "int_rx_mod",
+	    CTLFLAG_RW, &sc->ste_int_rx_mod, 0, "ste RX interrupt moderation");
+	/* Pull in device tunables. */
+	sc->ste_int_rx_mod = STE_IM_RX_TIMER_DEFAULT;
+	resource_int_value(device_get_name(sc->ste_dev),
+	    device_get_unit(sc->ste_dev), "int_rx_mod", &sc->ste_int_rx_mod);
+
 	tree = SYSCTL_ADD_NODE(ctx, child, OID_AUTO, "stats", CTLFLAG_RD,
 	    NULL, "STE statistics");
 	parent = SYSCTL_CHILDREN(tree);