e1000: Maybe stop TX if not enough free descriptors

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>

1 files changed, 42 insertions, 10 deletions

diff --git a/drivers/net/e1000/e1000_main.c b/drivers/net/e1000/e1000_main.c
index a1f5b0605363..e8a760802070 100644
--- a/drivers/net/e1000/e1000_main.c
+++ b/drivers/net/e1000/e1000_main.c
@@ -2899,6 +2899,35 @@ e1000_transfer_dhcp_info(struct e1000_adapter *adapter, struct sk_buff *skb)
         return 0;
 }
 
+static int __e1000_maybe_stop_tx(struct net_device *netdev, int size)
+{
+        struct e1000_adapter *adapter = netdev_priv(netdev);
+        struct e1000_tx_ring *tx_ring = adapter->tx_ring;
+
+        netif_stop_queue(netdev);
+        /* Herbert's original patch had:
+         *  smp_mb__after_netif_stop_queue();
+         * but since that doesn't exist yet, just open code it. */
+        smp_mb();
+
+        /* We need to check again in a case another CPU has just
+         * made room available. */
+        if (likely(E1000_DESC_UNUSED(tx_ring) < size))
+                return -EBUSY;
+
+        /* A reprieve! */
+        netif_start_queue(netdev);
+        return 0;
+}
+
+static int e1000_maybe_stop_tx(struct net_device *netdev,
+                               struct e1000_tx_ring *tx_ring, int size)
+{
+        if (likely(E1000_DESC_UNUSED(tx_ring) >= size))
+                return 0;
+        return __e1000_maybe_stop_tx(netdev, size);
+}
+
 #define TXD_USE_COUNT(S, X) (((S) >> (X)) + 1 )
 static int
 e1000_xmit_frame(struct sk_buff *skb, struct net_device *netdev)
@@ -2917,6 +2946,10 @@ e1000_xmit_frame(struct sk_buff *skb, struct net_device *netdev)
         unsigned int f;
         len -= skb->data_len;
 
+        /* This goes back to the question of how to logically map a tx queue
+         * to a flow.  Right now, performance is impacted slightly negatively
+         * if using multiple tx queues.  If the stack breaks away from a
+         * single qdisc implementation, we can look at this again. */
         tx_ring = adapter->tx_ring;
 
         if (unlikely(skb->len <= 0)) {
@@ -3012,8 +3045,7 @@ e1000_xmit_frame(struct sk_buff *skb, struct net_device *netdev)
 
         /* need: count + 2 desc gap to keep tail from touching
          * head, otherwise try next time */
-        if (unlikely(E1000_DESC_UNUSED(tx_ring) < count + 2)) {
-                netif_stop_queue(netdev);
+        if (unlikely(e1000_maybe_stop_tx(netdev, tx_ring, count + 2))) {
                 spin_unlock_irqrestore(&tx_ring->tx_lock, flags);
                 return NETDEV_TX_BUSY;
         }
@@ -3060,8 +3092,7 @@ e1000_xmit_frame(struct sk_buff *skb, struct net_device *netdev)
         netdev->trans_start = jiffies;
 
         /* Make sure there is space in the ring for the next send. */
-        if (unlikely(E1000_DESC_UNUSED(tx_ring) < MAX_SKB_FRAGS + 2))
-                netif_stop_queue(netdev);
+        e1000_maybe_stop_tx(netdev, tx_ring, MAX_SKB_FRAGS + 2);
 
         spin_unlock_irqrestore(&tx_ring->tx_lock, flags);
         return NETDEV_TX_OK;
@@ -3556,13 +3587,14 @@ e1000_clean_tx_irq(struct e1000_adapter *adapter,
         tx_ring->next_to_clean = i;
 
 #define TX_WAKE_THRESHOLD 32
-        if (unlikely(cleaned && netif_queue_stopped(netdev) &&
-                     netif_carrier_ok(netdev))) {
-                spin_lock(&tx_ring->tx_lock);
-                if (netif_queue_stopped(netdev) &&
-                    (E1000_DESC_UNUSED(tx_ring) >= TX_WAKE_THRESHOLD))
+        if (unlikely(cleaned && netif_carrier_ok(netdev) &&
+                     E1000_DESC_UNUSED(tx_ring) >= TX_WAKE_THRESHOLD)) {
+                /* Make sure that anybody stopping the queue after this
+                 * sees the new next_to_clean.
+                 */
+                smp_mb();
+                if (netif_queue_stopped(netdev))
                         netif_wake_queue(netdev);
-                spin_unlock(&tx_ring->tx_lock);
         }
 
         if (adapter->detect_tx_hung) {