[PATCH net-next] net: dev: introduce netdev_drop_inc()

[Yajun Deng]

We will use 'sudo perf record -g -a -e skb:kfree_skb' command to trace
the dropped packets when dropped increase in the output of ifconfig.
But there are two cases, one is only called kfree_skb(), another is
increasing the dropped and called kfree_skb(). The latter is what
we need. So we need to separate these two cases.

>From the other side, the dropped packet came from the core network and
the driver, we also need to separate these two cases.

Add netdev_drop_inc() and add a tracepoint for the core network dropped
packets. use 'sudo perf record -g -a -e net:netdev_drop' and 'sudo perf
 script' will recored the dropped packets by the core network.

Signed-off-by: Yajun Deng <yajun.deng@xxxxxxxxx>
---
 include/linux/netdevice.h  |  7 +++++++
 include/trace/events/net.h | 27 +++++++++++++++++++++++++++
 net/core/dev.c             | 30 ++++++++++++++++++++++++------
 3 files changed, 58 insertions(+), 6 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 3fb6fb67ed77..f7e8b1e33076 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2285,6 +2285,13 @@ struct net_device {
 };
 #define to_net_dev(d) container_of(d, struct net_device, dev)
 
+enum netdev_drop {
+	NETDEV_RX_DROPPED,
+	NETDEV_TX_DROPPED,
+	NETDEV_RX_NOHANDLER,
+};
+void netdev_drop_inc(struct net_device *dev, enum netdev_drop drop);
+
 static inline bool netif_elide_gro(const struct net_device *dev)
 {
 	if (!(dev->features & NETIF_F_GRO) || dev->xdp_prog)
diff --git a/include/trace/events/net.h b/include/trace/events/net.h
index 78c448c6ab4c..0f8e9762a856 100644
--- a/include/trace/events/net.h
+++ b/include/trace/events/net.h
@@ -118,6 +118,33 @@ TRACE_EVENT(net_dev_xmit_timeout,
 		__get_str(name), __get_str(driver), __entry->queue_index)
 );
 
+TRACE_EVENT(netdev_drop,
+
+	TP_PROTO(struct net_device *dev, void *location),
+
+	TP_ARGS(dev, location),
+
+	TP_STRUCT__entry(
+		__string(name,          dev->name)
+		__field(void *,         location)
+		__field(unsigned long,  rx_dropped)
+		__field(unsigned long,  tx_dropped)
+		__field(unsigned long,  rx_nohandler)
+	),
+
+	TP_fast_assign(
+		__assign_str(name, dev->name);
+		__entry->location     = location;
+		__entry->rx_dropped   = (unsigned long)atomic_long_read(&dev->rx_dropped);
+		__entry->tx_dropped   = (unsigned long)atomic_long_read(&dev->tx_dropped);
+		__entry->rx_nohandler = (unsigned long)atomic_long_read(&dev->rx_nohandler);
+	),
+
+	TP_printk("dev=%s rx_dropped=%lu tx_dropped=%lu rx_nohandler=%lu location=%p",
+		  __get_str(name), __entry->rx_dropped, __entry->tx_dropped, __entry->rx_nohandler,
+		  __entry->location)
+);
+
 DECLARE_EVENT_CLASS(net_dev_template,
 
 	TP_PROTO(struct sk_buff *skb),
diff --git a/net/core/dev.c b/net/core/dev.c
index f662c6a7d7b4..213f9d1eaa8d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -392,6 +392,24 @@ static void unlist_netdevice(struct net_device *dev)
 	dev_base_seq_inc(dev_net(dev));
 }
 
+void netdev_drop_inc(struct net_device *dev, enum netdev_drop drop)
+{
+	switch (drop) {
+	case NETDEV_RX_DROPPED:
+		atomic_long_inc(&dev->rx_dropped);
+		break;
+	case NETDEV_TX_DROPPED:
+		atomic_long_inc(&dev->tx_dropped);
+		break;
+	case NETDEV_RX_NOHANDLER:
+		atomic_long_inc(&dev->rx_nohandler);
+		break;
+	default:
+		break;
+	}
+	trace_netdev_drop(dev, __builtin_return_address(0));
+}
+EXPORT_SYMBOL(netdev_drop_inc);
 /*
  *	Our notifier list
  */
@@ -3586,7 +3604,7 @@ static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device
 out_kfree_skb:
 	kfree_skb(skb);
 out_null:
-	atomic_long_inc(&dev->tx_dropped);
+	netdev_drop_inc(dev, NETDEV_TX_DROPPED);
 	return NULL;
 }
 
@@ -4136,7 +4154,7 @@ static int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
 	rc = -ENETDOWN;
 	rcu_read_unlock_bh();
 
-	atomic_long_inc(&dev->tx_dropped);
+	netdev_drop_inc(dev, NETDEV_TX_DROPPED);
 	kfree_skb_list(skb);
 	return rc;
 out:
@@ -4188,7 +4206,7 @@ int __dev_direct_xmit(struct sk_buff *skb, u16 queue_id)
 	local_bh_enable();
 	return ret;
 drop:
-	atomic_long_inc(&dev->tx_dropped);
+	netdev_drop_inc(dev, NETDEV_TX_DROPPED);
 	kfree_skb_list(skb);
 	return NET_XMIT_DROP;
 }
@@ -4557,7 +4575,7 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
 
 	local_irq_restore(flags);
 
-	atomic_long_inc(&skb->dev->rx_dropped);
+	netdev_drop_inc(skb->dev, NETDEV_RX_DROPPED);
 	kfree_skb(skb);
 	return NET_RX_DROP;
 }
@@ -5319,9 +5337,9 @@ static int __netif_receive_skb_core(struct sk_buff **pskb, bool pfmemalloc,
 	} else {
 drop:
 		if (!deliver_exact)
-			atomic_long_inc(&skb->dev->rx_dropped);
+			netdev_drop_inc(skb->dev, NETDEV_RX_DROPPED);
 		else
-			atomic_long_inc(&skb->dev->rx_nohandler);
+			netdev_drop_inc(skb->dev, NETDEV_RX_NOHANDLER);
 		kfree_skb(skb);
 		/* Jamal, now you will not able to escape explaining
 		 * me how you were going to use this. :-)
-- 
2.25.1