jme: Improve tiny packets transmission performance on low frequency CPU

Update TXCSR register a little bit often; mainly to improve timeliness of
packets transmission:
The TXCSR register is updated after certain amount of TX descriptors are
added to the hardware TX ring.  The default value of the amount of TX
descriptors are 16.  This value could be further tuned by per-device sysctl
node hw.jmeX.tx_wreg.

The default value improves tiny packets transmission performance w/ JMC250
on AMD970@2200Mhz (831Kpps -> 911Kpps), on AMD970@800Mhz (484Kpps -> 834Kpps)
and it does not increase CPU usage on AMD970@3500Mhz (CPU usage stays @26%,
JMC250 could only do 911Kpps).

diff --git a/sys/dev/netif/jme/if_jme.c b/sys/dev/netif/jme/if_jme.c
index 9855f9f..b25b427 100644 (file)
--- a/sys/dev/netif/jme/if_jme.c
+++ b/sys/dev/netif/jme/if_jme.c
@@ -145,7 +145,7 @@ static int  jme_init_rx_ring(struct jme_rxdata *);
 static void    jme_init_tx_ring(struct jme_txdata *);
 static void    jme_init_ssb(struct jme_softc *);
 static int     jme_newbuf(struct jme_rxdata *, struct jme_rxdesc *, int);
-static int     jme_encap(struct jme_txdata *, struct mbuf **);
+static int     jme_encap(struct jme_txdata *, struct mbuf **, int *);
 static void    jme_rxpkt(struct jme_rxdata *);
 static int     jme_rxring_dma_alloc(struct jme_rxdata *);
 static int     jme_rxbuf_dma_alloc(struct jme_rxdata *);
@@ -972,6 +972,8 @@ jme_attach(device_t dev)
        if (coal_max < sc->jme_rx_coal_pkt)
                sc->jme_rx_coal_pkt = coal_max;
 
+       sc->jme_cdata.jme_tx_data.jme_tx_wreg = 16;
+
        /*
         * Create sysctl tree
         */
@@ -1159,6 +1161,11 @@ jme_sysctl_node(struct jme_softc *sc)
                       "rx_ring_count", CTLFLAG_RD,
                       &sc->jme_cdata.jme_rx_ring_cnt,
                       0, "RX ring count");
+       SYSCTL_ADD_INT(&sc->jme_sysctl_ctx,
+                      SYSCTL_CHILDREN(sc->jme_sysctl_tree), OID_AUTO,
+                      "tx_wreg", CTLFLAG_RW,
+                      &sc->jme_cdata.jme_tx_data.jme_tx_wreg, 0,
+                      "# of segments before writing to hardware register");
 
 #ifdef JME_RSS_DEBUG
        SYSCTL_ADD_INT(&sc->jme_sysctl_ctx,
@@ -1650,7 +1657,7 @@ jme_tso_pullup(struct mbuf **mp)
 }
 
 static int
-jme_encap(struct jme_txdata *tdata, struct mbuf **m_head)
+jme_encap(struct jme_txdata *tdata, struct mbuf **m_head, int *segs_used)
 {
        struct jme_txdesc *txd;
        struct jme_desc *desc;
@@ -1689,6 +1696,7 @@ jme_encap(struct jme_txdata *tdata, struct mbuf **m_head)
                        txsegs, maxsegs, &nsegs, BUS_DMA_NOWAIT);
        if (error)
                goto fail;
+       *segs_used += nsegs;
 
        bus_dmamap_sync(tdata->jme_tx_tag, txd->tx_dmamap,
                        BUS_DMASYNC_PREWRITE);
@@ -1730,6 +1738,8 @@ jme_encap(struct jme_txdata *tdata, struct mbuf **m_head)
                desc->buflen = htole32(mss);
                desc->addr_lo = 0;
 
+               *segs_used += 1;
+
                /* No effective TX desc is consumed */
                i = 0;
        } else {
@@ -1825,19 +1835,27 @@ jme_start(struct ifnet *ifp)
                 * don't have room, set the OACTIVE flag and wait
                 * for the NIC to drain the ring.
                 */
-               if (jme_encap(tdata, &m_head)) {
+               if (jme_encap(tdata, &m_head, &enq)) {
                        KKASSERT(m_head == NULL);
                        ifp->if_oerrors++;
                        ifp->if_flags |= IFF_OACTIVE;
                        break;
                }
-               enq++;
+
+               if (enq >= tdata->jme_tx_wreg) {
+                       CSR_WRITE_4(sc, JME_TXCSR, sc->jme_txcsr |
+                           TXCSR_TX_ENB | TXCSR_TXQ_N_START(TXCSR_TXQ0));
+                       enq = 0;
+               }
 
                /*
                 * If there's a BPF listener, bounce a copy of this frame
                 * to him.
                 */
                ETHER_BPF_MTAP(ifp, m_head);
+
+               /* Set a timeout in case the chip goes out to lunch. */
+               ifp->if_timer = JME_TX_TIMEOUT;
        }
 
        if (enq > 0) {
@@ -1849,8 +1867,6 @@ jme_start(struct ifnet *ifp)
                 */
                CSR_WRITE_4(sc, JME_TXCSR, sc->jme_txcsr | TXCSR_TX_ENB |
                    TXCSR_TXQ_N_START(TXCSR_TXQ0));
-               /* Set a timeout in case the chip goes out to lunch. */
-               ifp->if_timer = JME_TX_TIMEOUT;
        }
 }
 

diff --git a/sys/dev/netif/jme/if_jmevar.h b/sys/dev/netif/jme/if_jmevar.h
index 6ff9e98..6941d23 100644 (file)
--- a/sys/dev/netif/jme/if_jmevar.h
+++ b/sys/dev/netif/jme/if_jmevar.h
@@ -173,6 +173,7 @@ struct jme_txdata {
 
        struct jme_desc         *jme_tx_ring;
 
+       int                     jme_tx_wreg;
        int                     jme_tx_prod;
        int                     jme_tx_cons;
        int                     jme_tx_cnt;