r8169: add support for xmit_more

Delay update of hw tail descriptor if we know that another skb is going
to be sent.
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/r8169.c

@@ -7049,6 +7049,7 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 	u32 status, len;
 	u32 opts[2];
 	int frags;
+	bool stop_queue;
 
 	if (unlikely(!TX_FRAGS_READY_FOR(tp, skb_shinfo(skb)->nr_frags))) {
 		netif_err(tp, drv, dev, "BUG! Tx Ring full when queue awake!\n");
@@ -7105,11 +7106,16 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 
 	tp->cur_tx += frags + 1;
 
-	RTL_W8(TxPoll, NPQ);
+	stop_queue = !TX_FRAGS_READY_FOR(tp, MAX_SKB_FRAGS);
 
-	mmiowb();
+	if (!skb->xmit_more || stop_queue ||
+	    netif_xmit_stopped(netdev_get_tx_queue(dev, 0))) {
+		RTL_W8(TxPoll, NPQ);
+
+		mmiowb();
+	}
 
-	if (!TX_FRAGS_READY_FOR(tp, MAX_SKB_FRAGS)) {
+	if (stop_queue) {
 		/* Avoid wrongly optimistic queue wake-up: rtl_tx thread must
 		 * not miss a ring update when it notices a stopped queue.
 		 */