ixgb: recalculate after how many descriptors to wake the queue

Recalculate when to wake the queue using DESC_NEEDED instead of a
static hardcoded number.
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>

drivers/net/ixgb/ixgb.h

@@ -110,9 +110,6 @@ struct ixgb_adapter;
 #define IXGB_RXBUFFER_8192  8192
 #define IXGB_RXBUFFER_16384 16384
 
-/* How many Tx Descriptors do we need to call netif_wake_queue? */
-#define IXGB_TX_QUEUE_WAKE 16
-
 /* How many Rx Buffers do we bundle into one write to the hardware ? */
 #define IXGB_RX_BUFFER_WRITE	4	/* Must be power of 2 */
 

drivers/net/ixgb/ixgb_main.c

@@ -1787,7 +1787,7 @@ ixgb_clean_tx_irq(struct ixgb_adapter *adapter)
 	if (unlikely(netif_queue_stopped(netdev))) {
 		spin_lock(&adapter->tx_lock);
 		if (netif_queue_stopped(netdev) && netif_carrier_ok(netdev) &&
-		    (IXGB_DESC_UNUSED(tx_ring) > IXGB_TX_QUEUE_WAKE))
+		    (IXGB_DESC_UNUSED(tx_ring) >= DESC_NEEDED))
 			netif_wake_queue(netdev);
 		spin_unlock(&adapter->tx_lock);
 	}