i40e: skb->xmit_more support

Support skb->xmit_more in i40e is straightforward : we need to move
around i40e_maybe_stop_tx() call to correctly test netif_xmit_stopped()
before taking the decision to not kick the NIC.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -2052,6 +2052,47 @@ static void i40e_create_tx_ctx(struct i40e_ring *tx_ring,
 	context_desc->type_cmd_tso_mss = cpu_to_le64(cd_type_cmd_tso_mss);
 }
 
+/**
+ * __i40e_maybe_stop_tx - 2nd level check for tx stop conditions
+ * @tx_ring: the ring to be checked
+ * @size:    the size buffer we want to assure is available
+ *
+ * Returns -EBUSY if a stop is needed, else 0
+ **/
+static inline int __i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
+{
+	netif_stop_subqueue(tx_ring->netdev, tx_ring->queue_index);
+	/* Memory barrier before checking head and tail */
+	smp_mb();
+
+	/* Check again in a case another CPU has just made room available. */
+	if (likely(I40E_DESC_UNUSED(tx_ring) < size))
+		return -EBUSY;
+
+	/* A reprieve! - use start_queue because it doesn't call schedule */
+	netif_start_subqueue(tx_ring->netdev, tx_ring->queue_index);
+	++tx_ring->tx_stats.restart_queue;
+	return 0;
+}
+
+/**
+ * i40e_maybe_stop_tx - 1st level check for tx stop conditions
+ * @tx_ring: the ring to be checked
+ * @size:    the size buffer we want to assure is available
+ *
+ * Returns 0 if stop is not needed
+ **/
+#ifdef I40E_FCOE
+int i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
+#else
+static int i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
+#endif
+{
+	if (likely(I40E_DESC_UNUSED(tx_ring) >= size))
+		return 0;
+	return __i40e_maybe_stop_tx(tx_ring, size);
+}
+
 /**
  * i40e_tx_map - Build the Tx descriptor
  * @tx_ring:  ring to send buffer on
@@ -2195,8 +2236,12 @@ static void i40e_tx_map(struct i40e_ring *tx_ring, struct sk_buff *skb,
 
 	tx_ring->next_to_use = i;
 
+	i40e_maybe_stop_tx(tx_ring, DESC_NEEDED);
 	/* notify HW of packet */
-	writel(i, tx_ring->tail);
+	if (!skb->xmit_more ||
+	    netif_xmit_stopped(netdev_get_tx_queue(tx_ring->netdev,
+						   tx_ring->queue_index)))
+		writel(i, tx_ring->tail);
 
 	return;
 
@@ -2217,47 +2262,6 @@ dma_error:
 	tx_ring->next_to_use = i;
 }
 
-/**
- * __i40e_maybe_stop_tx - 2nd level check for tx stop conditions
- * @tx_ring: the ring to be checked
- * @size:    the size buffer we want to assure is available
- *
- * Returns -EBUSY if a stop is needed, else 0
- **/
-static inline int __i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
-{
-	netif_stop_subqueue(tx_ring->netdev, tx_ring->queue_index);
-	/* Memory barrier before checking head and tail */
-	smp_mb();
-
-	/* Check again in a case another CPU has just made room available. */
-	if (likely(I40E_DESC_UNUSED(tx_ring) < size))
-		return -EBUSY;
-
-	/* A reprieve! - use start_queue because it doesn't call schedule */
-	netif_start_subqueue(tx_ring->netdev, tx_ring->queue_index);
-	++tx_ring->tx_stats.restart_queue;
-	return 0;
-}
-
-/**
- * i40e_maybe_stop_tx - 1st level check for tx stop conditions
- * @tx_ring: the ring to be checked
- * @size:    the size buffer we want to assure is available
- *
- * Returns 0 if stop is not needed
- **/
-#ifdef I40E_FCOE
-int i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
-#else
-static int i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
-#endif
-{
-	if (likely(I40E_DESC_UNUSED(tx_ring) >= size))
-		return 0;
-	return __i40e_maybe_stop_tx(tx_ring, size);
-}
-
 /**
  * i40e_xmit_descriptor_count - calculate number of tx descriptors needed
  * @skb:     send buffer
@@ -2372,8 +2376,6 @@ static netdev_tx_t i40e_xmit_frame_ring(struct sk_buff *skb,
 	i40e_tx_map(tx_ring, skb, first, tx_flags, hdr_len,
 		    td_cmd, td_offset);
 
-	i40e_maybe_stop_tx(tx_ring, DESC_NEEDED);
-
 	return NETDEV_TX_OK;
 
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