[TG3]: Minimize locking in TX path.

This is similar to Eric Dumazet's tx_lock patch for tg3 but takes it
one step further to eliminate the tx_lock in the tx_completion path
when the tx queue is not stopped.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
index af8263a1580ea5b6fca000c5ea59b2cd3af7a4af..e877579aab38781e230959ae8167f9082d40904f 100644 (file)
--- a/drivers/net/tg3.c
+++ b/drivers/net/tg3.c
@@ -121,12 +121,9 @@
                                   TG3_RX_RCB_RING_SIZE(tp))
 #define TG3_TX_RING_BYTES      (sizeof(struct tg3_tx_buffer_desc) * \
                                 TG3_TX_RING_SIZE)
-#define TX_RING_GAP(TP)        \
-       (TG3_TX_RING_SIZE - (TP)->tx_pending)
 #define TX_BUFFS_AVAIL(TP)                                             \
-       (((TP)->tx_cons <= (TP)->tx_prod) ?                             \
-         (TP)->tx_cons + (TP)->tx_pending - (TP)->tx_prod :            \
-         (TP)->tx_cons - (TP)->tx_prod - TX_RING_GAP(TP))
+       ((TP)->tx_pending -                                             \
+        (((TP)->tx_prod - (TP)->tx_cons) & (TG3_TX_RING_SIZE - 1)))
 #define NEXT_TX(N)             (((N) + 1) & (TG3_TX_RING_SIZE - 1))
 
 #define RX_PKT_BUF_SZ          (1536 + tp->rx_offset + 64)
@@ -2880,9 +2877,13 @@ static void tg3_tx(struct tg3 *tp)
 
        tp->tx_cons = sw_idx;
 
-       if (netif_queue_stopped(tp->dev) &&
-           (TX_BUFFS_AVAIL(tp) > TG3_TX_WAKEUP_THRESH))
-               netif_wake_queue(tp->dev);
+       if (unlikely(netif_queue_stopped(tp->dev))) {
+               spin_lock(&tp->tx_lock);
+               if (netif_queue_stopped(tp->dev) &&
+                   (TX_BUFFS_AVAIL(tp) > TG3_TX_WAKEUP_THRESH))
+                       netif_wake_queue(tp->dev);
+               spin_unlock(&tp->tx_lock);
+       }
 }
 
 /* Returns size of skb allocated or < 0 on error.
@@ -3198,9 +3199,7 @@ static int tg3_poll(struct net_device *netdev, int *budget)
 
        /* run TX completion thread */
        if (sblk->idx[0].tx_consumer != tp->tx_cons) {
-               spin_lock(&tp->tx_lock);
                tg3_tx(tp);
-               spin_unlock(&tp->tx_lock);
        }
 
        /* run RX thread, within the bounds set by NAPI.
@@ -3716,8 +3715,11 @@ static int tg3_start_xmit(struct sk_buff *skb, struct net_device *dev)
        tw32_tx_mbox((MAILBOX_SNDHOST_PROD_IDX_0 + TG3_64BIT_REG_LOW), entry);
 
        tp->tx_prod = entry;
-       if (TX_BUFFS_AVAIL(tp) <= (MAX_SKB_FRAGS + 1))
+       if (TX_BUFFS_AVAIL(tp) <= (MAX_SKB_FRAGS + 1)) {
                netif_stop_queue(dev);
+               if (TX_BUFFS_AVAIL(tp) > TG3_TX_WAKEUP_THRESH)
+                       netif_wake_queue(tp->dev);
+       }
 
 out_unlock:
        mmiowb();