mlx4: exploit skb->xmit_more to conditionally send doorbell

skb->xmit_more tells us if another skb is coming next.

We need to send doorbell when : xmit_more is not set,
or txqueue is stopped (preventing next skb to come immediately)

Tested with a modified pktgen version, I got a 40% increase of
throughput.

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

1 files changed, 16 insertions, 7 deletions

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
index c44f4237b9be..adedc47e947d 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
@@ -667,6 +667,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
         int lso_header_size;
         void *fragptr;
         bool bounce = false;
+        bool send_doorbell;
 
         if (!priv->port_up)
                 goto tx_drop;
@@ -878,12 +879,16 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
 
         skb_tx_timestamp(skb);
 
-        if (ring->bf_enabled && desc_size <= MAX_BF && !bounce && !vlan_tx_tag_present(skb)) {
+        send_doorbell = !skb->xmit_more || netif_xmit_stopped(ring->tx_queue);
+
+        if (ring->bf_enabled && desc_size <= MAX_BF && !bounce &&
+            !vlan_tx_tag_present(skb) && send_doorbell) {
                 tx_desc->ctrl.bf_qpn |= cpu_to_be32(ring->doorbell_qpn);
 
                 op_own |= htonl((bf_index & 0xffff) << 8);
-                /* Ensure new descirptor hits memory
-                * before setting ownership of this descriptor to HW */
+                /* Ensure new descriptor hits memory
+                 * before setting ownership of this descriptor to HW
+                 */
                 wmb();
                 tx_desc->ctrl.owner_opcode = op_own;
 
@@ -896,12 +901,16 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
 
                 ring->bf.offset ^= ring->bf.buf_size;
         } else {
-                /* Ensure new descirptor hits memory
-                * before setting ownership of this descriptor to HW */
+                /* Ensure new descriptor hits memory
+                 * before setting ownership of this descriptor to HW
+                 */
                 wmb();
                 tx_desc->ctrl.owner_opcode = op_own;
-                wmb();
-                iowrite32be(ring->doorbell_qpn, ring->bf.uar->map + MLX4_SEND_DOORBELL);
+                if (send_doorbell) {
+                        wmb();
+                        iowrite32be(ring->doorbell_qpn,
+                                    ring->bf.uar->map + MLX4_SEND_DOORBELL);
+                }
         }
 
         return NETDEV_TX_OK;