[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>

1 files changed, 13 insertions, 11 deletions

diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
index af8263a1580e..e877579aab38 100644
--- 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();