packet: rework packet_pick_tx_queue() to use common code selection

Currently packet_pick_tx_queue() is the only caller of
ndo_select_queue() using a fallback argument other than
netdev_pick_tx.

Leveraging rx queue, we can obtain a similar queue selection
behavior using core helpers. After this change, ndo_select_queue()
is always invoked with netdev_pick_tx() as fallback.
We can change ndo_select_queue() signature in a followup patch,
dropping an indirect call per transmitted packet in some scenarios
(e.g. TCP syn and XDP generic xmit)

This changes slightly how af packet queue selection happens when
PACKET_QDISC_BYPASS is set. It's now more similar to plan dev_queue_xmit()
tacking in account both XPS and TC mapping.

 v1  -> v2:
  - rebased after helper name change
 RFC -> v1:
  - initialize sender_cpu to the expected value
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -2152,6 +2152,8 @@ static inline void netdev_for_each_tx_queue(struct net_device *dev,
 				  &qdisc_xmit_lock_key);	\
 }
 
+u16 netdev_pick_tx(struct net_device *dev, struct sk_buff *skb,
+		     struct net_device *sb_dev);
 struct netdev_queue *netdev_core_pick_tx(struct net_device *dev,
 					 struct sk_buff *skb,
 					 struct net_device *sb_dev);

net/core/dev.c

@@ -3704,7 +3704,7 @@ u16 dev_pick_tx_cpu_id(struct net_device *dev, struct sk_buff *skb,
 }
 EXPORT_SYMBOL(dev_pick_tx_cpu_id);
 
-static u16 netdev_pick_tx(struct net_device *dev, struct sk_buff *skb,
+u16 netdev_pick_tx(struct net_device *dev, struct sk_buff *skb,
 		     struct net_device *sb_dev)
 {
 	struct sock *sk = skb->sk;
@@ -3729,6 +3729,7 @@ static u16 netdev_pick_tx(struct net_device *dev, struct sk_buff *skb,
 
 	return queue_index;
 }
+EXPORT_SYMBOL(netdev_pick_tx);
 
 struct netdev_queue *netdev_core_pick_tx(struct net_device *dev,
 					 struct sk_buff *skb,

net/packet/af_packet.c

@@ -275,24 +275,23 @@ static bool packet_use_direct_xmit(const struct packet_sock *po)
 	return po->xmit == packet_direct_xmit;
 }
 
-static u16 __packet_pick_tx_queue(struct net_device *dev, struct sk_buff *skb,
-				  struct net_device *sb_dev)
-{
-	return dev_pick_tx_cpu_id(dev, skb, sb_dev, NULL);
-}
-
 static u16 packet_pick_tx_queue(struct sk_buff *skb)
 {
 	struct net_device *dev = skb->dev;
 	const struct net_device_ops *ops = dev->netdev_ops;
+	int cpu = raw_smp_processor_id();
 	u16 queue_index;
 
+#ifdef CONFIG_XPS
+	skb->sender_cpu = cpu + 1;
+#endif
+	skb_record_rx_queue(skb, cpu % dev->real_num_tx_queues);
 	if (ops->ndo_select_queue) {
 		queue_index = ops->ndo_select_queue(dev, skb, NULL,
-						    __packet_pick_tx_queue);
+						    netdev_pick_tx);
 		queue_index = netdev_cap_txqueue(dev, queue_index);
 	} else {
-		queue_index = __packet_pick_tx_queue(dev, skb, NULL);
+		queue_index = netdev_pick_tx(dev, skb, NULL);
 	}
 
 	return queue_index;