bce: Improve tiny packets transmission performance on low frequency CPU

Update TX HOST_IDX and HOST_BSEQ registers a little bit often; mainly to
improve timeliness of packets transmission:
The TX HOST_IDX and HOST_BSEQ registers are updated after certain amount
of TX descriptors are added to the hardware TX ring.  The default value
of the amount of TX descriptors are 8.  This value could be further
tuned by per-device sysctl node hw.bceX.tx_wreg.

The default value greatly improves tiny packets transmission performance
w/ 5709C on AMD970@800Mhz (513Kpps -> 1Mpps) and it does not increase CPU
usage on AMD970@3500Mhz (CPU usage stays @24%, 5709C could only do 1Mpps).

diff --git a/sys/dev/netif/bce/if_bce.c b/sys/dev/netif/bce/if_bce.c
index ca6e083..4d28c55 100644 (file)
--- a/sys/dev/netif/bce/if_bce.c
+++ b/sys/dev/netif/bce/if_bce.c
@@ -413,7 +413,7 @@ static int  bce_init_rx_chain(struct bce_softc *);
 static void    bce_free_rx_chain(struct bce_softc *);
 static void    bce_free_tx_chain(struct bce_softc *);
 
-static int     bce_encap(struct bce_softc *, struct mbuf **);
+static int     bce_encap(struct bce_softc *, struct mbuf **, int *);
 static int     bce_tso_setup(struct bce_softc *, struct mbuf **,
                    uint16_t *, uint16_t *);
 static void    bce_start(struct ifnet *);
@@ -929,6 +929,7 @@ bce_attach(device_t dev)
        sc->bce_rx_ticks_int           = bce_rx_ticks_int;
        sc->bce_rx_ticks               = bce_rx_ticks;
 #endif
+       sc->tx_wreg = 8;
 
        /* Update statistics once every second. */
        sc->bce_stats_ticks = 1000000 & 0xffff00;
@@ -4871,7 +4872,7 @@ bce_mgmt_init(struct bce_softc *sc)
 /*   0 for success, positive value for failure.                             */
 /****************************************************************************/
 static int
-bce_encap(struct bce_softc *sc, struct mbuf **m_head)
+bce_encap(struct bce_softc *sc, struct mbuf **m_head, int *nsegs_used)
 {
        bus_dma_segment_t segs[BCE_MAX_SEGMENTS];
        bus_dmamap_t map, tmp_map;
@@ -4920,6 +4921,8 @@ bce_encap(struct bce_softc *sc, struct mbuf **m_head)
                goto back;
        bus_dmamap_sync(sc->tx_mbuf_tag, map, BUS_DMASYNC_PREWRITE);
 
+       *nsegs_used += nsegs;
+
        /* Reset m0 */
        m0 = *m_head;
 
@@ -5027,7 +5030,7 @@ bce_start(struct ifnet *ifp)
                 * head of the queue and set the OACTIVE flag
                 * to wait for the NIC to drain the chain.
                 */
-               if (bce_encap(sc, &m_head)) {
+               if (bce_encap(sc, &m_head, &count)) {
                        ifp->if_oerrors++;
                        if (sc->used_tx_bd == 0) {
                                continue;
@@ -5037,30 +5040,28 @@ bce_start(struct ifnet *ifp)
                        }
                }
 
-               count++;
+               if (count >= sc->tx_wreg) {
+                       /* Start the transmit. */
+                       REG_WR16(sc, MB_GET_CID_ADDR(TX_CID) +
+                           BCE_L2CTX_TX_HOST_BIDX, sc->tx_prod);
+                       REG_WR(sc, MB_GET_CID_ADDR(TX_CID) +
+                           BCE_L2CTX_TX_HOST_BSEQ, sc->tx_prod_bseq);
+                       count = 0;
+               }
 
                /* Send a copy of the frame to any BPF listeners. */
                ETHER_BPF_MTAP(ifp, m_head);
-       }
 
-       if (count == 0) {
-               /* no packets were dequeued */
-               return;
+               /* Set the tx timeout. */
+               ifp->if_timer = BCE_TX_TIMEOUT;
+       }
+       if (count > 0) {
+               /* Start the transmit. */
+               REG_WR16(sc, MB_GET_CID_ADDR(TX_CID) + BCE_L2CTX_TX_HOST_BIDX,
+                   sc->tx_prod);
+               REG_WR(sc, MB_GET_CID_ADDR(TX_CID) + BCE_L2CTX_TX_HOST_BSEQ,
+                   sc->tx_prod_bseq);
        }
-
-#if 0
-       REG_WR(sc, BCE_MQ_COMMAND,
-           REG_RD(sc, BCE_MQ_COMMAND) | BCE_MQ_COMMAND_NO_MAP_ERROR);
-#endif
-
-       /* Start the transmit. */
-       REG_WR16(sc, MB_GET_CID_ADDR(TX_CID) + BCE_L2CTX_TX_HOST_BIDX,
-           sc->tx_prod);
-       REG_WR(sc, MB_GET_CID_ADDR(TX_CID) + BCE_L2CTX_TX_HOST_BSEQ,
-           sc->tx_prod_bseq);
-
-       /* Set the tx timeout. */
-       ifp->if_timer = BCE_TX_TIMEOUT;
 }
 
 
@@ -6206,6 +6207,10 @@ bce_add_sysctls(struct bce_softc *sc)
        SYSCTL_ADD_INT(ctx, children, OID_AUTO, "tx_pages",
                CTLFLAG_RD, &sc->tx_pages, 0, "# of TX pages");
 
+       SYSCTL_ADD_INT(ctx, children, OID_AUTO, "tx_wreg",
+               CTLFLAG_RW, &sc->tx_wreg, 0,
+               "# segments before write to hardware registers");
+
 #ifdef BCE_DEBUG
        SYSCTL_ADD_INT(ctx, children, OID_AUTO, 
                "rx_low_watermark",

diff --git a/sys/dev/netif/bce/if_bcereg.h b/sys/dev/netif/bce/if_bcereg.h
index fe1b08b..eaaf24d 100644 (file)
--- a/sys/dev/netif/bce/if_bcereg.h
+++ b/sys/dev/netif/bce/if_bcereg.h
@@ -5968,6 +5968,7 @@ struct bce_softc {
        uint16_t                rx_cons;
        uint32_t                rx_prod_bseq;   /* Counts the bytes used.  */
        int                     tx_pages;
+       int                     tx_wreg;
        uint16_t                tx_prod;
        uint16_t                tx_cons;
        uint32_t                tx_prod_bseq;   /* Counts the bytes used.  */