net: txq_trans_update() helper

We would like to get rid of netdev->trans_start = jiffies; that about all net
drivers have to use in their start_xmit() function, and use txq->trans_start
instead.

This can be done generically in core network, as suggested by David.

Some devices, (particularly loopback) dont need trans_start update, because
they dont have transmit watchdog. We could add a new device flag, or rely
on fact that txq->tran_start can be updated is txq->xmit_lock_owner is
different than -1. Use a helper function to hide our choice.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1674,6 +1674,12 @@ static inline void __netif_tx_unlock_bh(struct netdev_queue *txq)
 	spin_unlock_bh(&txq->_xmit_lock);
 }
 
+static inline void txq_trans_update(struct netdev_queue *txq)
+{
+	if (txq->xmit_lock_owner != -1)
+		txq->trans_start = jiffies;
+}
+
 /**
  *	netif_tx_lock - grab network device transmit lock
  *	@dev: network device

net/core/dev.c

@@ -1698,6 +1698,8 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
 			skb->dst = NULL;
 		}
 		rc = ops->ndo_start_xmit(skb, dev);
+		if (rc == 0)
+			txq_trans_update(txq);
 		/*
 		 * TODO: if skb_orphan() was called by
 		 * dev->hard_start_xmit() (for example, the unmodified
@@ -1727,6 +1729,7 @@ gso:
 			skb->next = nskb;
 			return rc;
 		}
+		txq_trans_update(txq);
 		if (unlikely(netif_tx_queue_stopped(txq) && skb->next))
 			return NETDEV_TX_BUSY;
 	} while (skb->next);

net/core/netpoll.c

@@ -302,8 +302,11 @@ static void netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
 		for (tries = jiffies_to_usecs(1)/USEC_PER_POLL;
 		     tries > 0; --tries) {
 			if (__netif_tx_trylock(txq)) {
-				if (!netif_tx_queue_stopped(txq))
+				if (!netif_tx_queue_stopped(txq)) {
 					status = ops->ndo_start_xmit(skb, dev);
+					if (status == NETDEV_TX_OK)
+						txq_trans_update(txq);
+				}
 				__netif_tx_unlock(txq);
 
 				if (status == NETDEV_TX_OK)

net/core/pktgen.c

@@ -3438,6 +3438,7 @@ static __inline__ void pktgen_xmit(struct pktgen_dev *pkt_dev)
 	      retry_now:
 		ret = (*xmit)(pkt_dev->skb, odev);
 		if (likely(ret == NETDEV_TX_OK)) {
+			txq_trans_update(txq);
 			pkt_dev->last_ok = 1;
 			pkt_dev->sofar++;
 			pkt_dev->seq_num++;

net/sched/sch_teql.c

@@ -308,6 +308,7 @@ restart:
 				if (!netif_tx_queue_stopped(slave_txq) &&
 				    !netif_tx_queue_frozen(slave_txq) &&
 				    slave_ops->ndo_start_xmit(skb, slave) == 0) {
+					txq_trans_update(slave_txq);
 					__netif_tx_unlock(slave_txq);
 					master->slaves = NEXT_SLAVE(q);
 					netif_wake_queue(dev);