net_sched: introduce tracepoint trace_qdisc_enqueue()

Tracepoint trace_qdisc_enqueue() is introduced to trace skb at
the entrance of TC layer on TX side. This is similar to
trace_qdisc_dequeue():

1. For both we only trace successful cases. The failure cases
   can be traced via trace_kfree_skb().

2. They are called at entrance or exit of TC layer, not for each
   ->enqueue() or ->dequeue(). This is intentional, because
   we want to make trace_qdisc_enqueue() symmetric to
   trace_qdisc_dequeue(), which is easier to use.

The return value of qdisc_enqueue() is not interesting here,
we have Qdisc's drop packets in ->dequeue(), it is impossible to
trace them even if we have the return value, the only way to trace
them is tracing kfree_skb().

We only add information we need to trace ring buffer. If any other
information is needed, it is easy to extend it without breaking ABI,
see commit 3dd344e ("net: tracepoint: exposing sk_family in all
tcp:tracepoints").

Reviewed-by: Cong Wang <[email protected]>
Signed-off-by: Qitao Xu <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

include/trace/events/qdisc.h

@@ -46,6 +46,32 @@ TRACE_EVENT(qdisc_dequeue,
  __entry->txq_state, __entry->packets, __entry->skbaddr )
 );
 
+TRACE_EVENT(qdisc_enqueue,
+
+ TP_PROTO(struct Qdisc *qdisc, const struct netdev_queue *txq, struct sk_buff *skb),
+
+ TP_ARGS(qdisc, txq, skb),
+
+ TP_STRUCT__entry(
+ __field(struct Qdisc *, qdisc)
+ __field(void *, skbaddr)
+ __field(int, ifindex)
+ __field(u32, handle)
+ __field(u32, parent)
+ ),
+
+ TP_fast_assign(
+ __entry->qdisc = qdisc;
+ __entry->skbaddr = skb;
+ __entry->ifindex = txq->dev ? txq->dev->ifindex : 0;
+ __entry->handle = qdisc->handle;
+ __entry->parent = qdisc->parent;
+ ),
+
+ TP_printk("enqueue ifindex=%d qdisc handle=0x%X parent=0x%X skbaddr=%px",
+ __entry->ifindex, __entry->handle, __entry->parent, __entry->skbaddr)
+);
+
 TRACE_EVENT(qdisc_reset,
 
  TP_PROTO(struct Qdisc *q),

net/core/dev.c

@@ -131,6 +131,7 @@
 #include <trace/events/napi.h>
 #include <trace/events/net.h>
 #include <trace/events/skb.h>
+#include <trace/events/qdisc.h>
 #include <linux/inetdevice.h>
 #include <linux/cpu_rmap.h>
 #include <linux/static_key.h>
@@ -3844,6 +3845,18 @@ static void qdisc_pkt_len_init(struct sk_buff *skb)
  }
 }
 
+static int dev_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *q,
+ struct sk_buff **to_free,
+ struct netdev_queue *txq)
+{
+ int rc;
+
+ rc = q->enqueue(skb, q, to_free) & NET_XMIT_MASK;
+ if (rc == NET_XMIT_SUCCESS)
+ trace_qdisc_enqueue(q, txq, skb);
+ return rc;
+}
+
 static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
  struct net_device *dev,
  struct netdev_queue *txq)
@@ -3862,8 +3875,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
  * of q->seqlock to protect from racing with requeuing.
  */
  if (unlikely(!nolock_qdisc_is_empty(q))) {
- rc = q->enqueue(skb, q, &to_free) &
- NET_XMIT_MASK;
+ rc = dev_qdisc_enqueue(skb, q, &to_free, txq);
  __qdisc_run(q);
  qdisc_run_end(q);
 
@@ -3879,7 +3891,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
  return NET_XMIT_SUCCESS;
  }
 
- rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
+ rc = dev_qdisc_enqueue(skb, q, &to_free, txq);
  qdisc_run(q);
 
 no_lock_out:
@@ -3923,7 +3935,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
  qdisc_run_end(q);
  rc = NET_XMIT_SUCCESS;
  } else {
- rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
+ rc = dev_qdisc_enqueue(skb, q, &to_free, txq);
  if (qdisc_run_begin(q)) {
  if (unlikely(contended)) {
  spin_unlock(&q->busylock);