netpoll: Respect NETIF_F_LLTX

Stop taking the transmit lock when a network device has specified
NETIF_F_LLTX.

If no locks needed to trasnmit a packet this is the ideal scenario for
netpoll as all packets can be trasnmitted immediately.

Even if some locks are needed in ndo_start_xmit skipping any unnecessary
serialization is desirable for netpoll as it makes it more likely a
debugging packet may be trasnmitted immediately instead of being
deferred until later.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 10 insertions, 5 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 0d8c8718980a..4cd5e9e13c87 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2909,6 +2909,11 @@ static inline void netif_tx_unlock_bh(struct net_device *dev)
         }                                               \
 }
 
+#define HARD_TX_TRYLOCK(dev, txq)                       \
+        (((dev->features & NETIF_F_LLTX) == 0) ?        \
+                __netif_tx_trylock(txq) :               \
+                true )
+
 #define HARD_TX_UNLOCK(dev, txq) {                      \
         if ((dev->features & NETIF_F_LLTX) == 0) {      \
                 __netif_tx_unlock(txq);                 \
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index d44af2306f23..ed7740f7a94d 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -119,17 +119,17 @@ static void queue_process(struct work_struct *work)
                 txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));
 
                 local_irq_save(flags);
-                __netif_tx_lock(txq, smp_processor_id());
+                HARD_TX_LOCK(dev, txq, smp_processor_id());
                 if (netif_xmit_frozen_or_stopped(txq) ||
                     netpoll_start_xmit(skb, dev, txq) != NETDEV_TX_OK) {
                         skb_queue_head(&npinfo->txq, skb);
-                        __netif_tx_unlock(txq);
+                        HARD_TX_UNLOCK(dev, txq);
                         local_irq_restore(flags);
 
                         schedule_delayed_work(&npinfo->tx_work, HZ/10);
                         return;
                 }
-                __netif_tx_unlock(txq);
+                HARD_TX_UNLOCK(dev, txq);
                 local_irq_restore(flags);
         }
 }
@@ -345,11 +345,11 @@ void netpoll_send_skb_on_dev(struct netpoll *np, struct sk_buff *skb,
                 /* try until next clock tick */
                 for (tries = jiffies_to_usecs(1)/USEC_PER_POLL;
                      tries > 0; --tries) {
-                        if (__netif_tx_trylock(txq)) {
+                        if (HARD_TX_TRYLOCK(dev, txq)) {
                                 if (!netif_xmit_stopped(txq))
                                         status = netpoll_start_xmit(skb, dev, txq);
 
-                                __netif_tx_unlock(txq);
+                                HARD_TX_UNLOCK(dev, txq);
 
                                 if (status == NETDEV_TX_OK)
                                         break;