net/mlx4_en: remove NETDEV_TX_BUSY

Drivers should avoid NETDEV_TX_BUSY as much as possible.

They should stop the tx queue before qdisc even tries to push another
packet, to avoid requeues.

For a driver supporting skb->xmit_more, this is likely to be a prereq
anyway, otherwise we could have a tx deadlock : We need to force a
doorbell if TX ring is full.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
index 92a7cf46d9af9260d601a0d65ec5bba49fdc3908..8726a4aee5a7405c6d58518b2aa44bdb30b9f5cb 100644 (file)
--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
@@ -706,6 +706,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
        void *fragptr = NULL;
        bool bounce = false;
        bool send_doorbell;
+       bool stop_queue;
        bool inline_ok;
        u32 ring_cons;
 
@@ -735,30 +736,6 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
        if (vlan_tx_tag_present(skb))
                vlan_tag = vlan_tx_tag_get(skb);
 
-       /* Check available TXBBs And 2K spare for prefetch */
-       if (unlikely(((int)(ring->prod - ring_cons)) >
-                    ring->size - HEADROOM - MAX_DESC_TXBBS)) {
-               /* every full Tx ring stops queue */
-               netif_tx_stop_queue(ring->tx_queue);
-               ring->queue_stopped++;
-
-               /* If queue was emptied after the if, and before the
-                * stop_queue - need to wake the queue, or else it will remain
-                * stopped forever.
-                * Need a memory barrier to make sure ring->cons was not
-                * updated before queue was stopped.
-                */
-               wmb();
-
-               ring_cons = ACCESS_ONCE(ring->cons);
-               if (unlikely(((int)(ring->prod - ring_cons)) <=
-                            ring->size - HEADROOM - MAX_DESC_TXBBS)) {
-                       netif_tx_wake_queue(ring->tx_queue);
-                       ring->wake_queue++;
-               } else {
-                       return NETDEV_TX_BUSY;
-               }
-       }
 
        prefetchw(&ring->tx_queue->dql);
 
@@ -929,6 +906,13 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
 
        skb_tx_timestamp(skb);
 
+       /* Check available TXBBs And 2K spare for prefetch */
+       stop_queue = (int)(ring->prod - ring_cons) >
+                     ring->size - HEADROOM - MAX_DESC_TXBBS;
+       if (unlikely(stop_queue)) {
+               netif_tx_stop_queue(ring->tx_queue);
+               ring->queue_stopped++;
+       }
        send_doorbell = !skb->xmit_more || netif_xmit_stopped(ring->tx_queue);
 
        real_size = (real_size / 16) & 0x3f;
@@ -973,6 +957,22 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
                }
        }
 
+       if (unlikely(stop_queue)) {
+               /* If queue was emptied after the if (stop_queue) , and before
+                * the netif_tx_stop_queue() - need to wake the queue,
+                * or else it will remain stopped forever.
+                * Need a memory barrier to make sure ring->cons was not
+                * updated before queue was stopped.
+                */
+               smp_rmb();
+
+               ring_cons = ACCESS_ONCE(ring->cons);
+               if (unlikely(((int)(ring->prod - ring_cons)) <=
+                            ring->size - HEADROOM - MAX_DESC_TXBBS)) {
+                       netif_tx_wake_queue(ring->tx_queue);
+                       ring->wake_queue++;
+               }
+       }
        return NETDEV_TX_OK;
 
 tx_drop_unmap: