net_sched: add a tracepoint for qdisc creation

With this tracepoint, we could know when qdisc's are created,
especially those default qdisc's.

Sample output:

  tc-736   [001] ...1    56.230107: qdisc_create: dev=ens3 kind=pfifo parent=1:0
  tc-736   [001] ...1    56.230113: qdisc_create: dev=ens3 kind=hfsc parent=ffff:ffff
  tc-738   [001] ...1    56.256816: qdisc_create: dev=ens3 kind=pfifo parent=1:100
  tc-739   [001] ...1    56.267584: qdisc_create: dev=ens3 kind=pfifo parent=1:200
  tc-740   [001] ...1    56.279649: qdisc_create: dev=ens3 kind=fq_codel parent=1:100
  tc-741   [001] ...1    56.289996: qdisc_create: dev=ens3 kind=pfifo_fast parent=1:200
  tc-745   [000] .N.1   111.687483: qdisc_create: dev=ens3 kind=ingress parent=ffff:fff1

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/trace/events/qdisc.h

@@ -96,6 +96,29 @@ TRACE_EVENT(qdisc_destroy,
 		  TC_H_MAJ(__entry->handle) >> 16, TC_H_MIN(__entry->handle))
 );
 
+TRACE_EVENT(qdisc_create,
+
+	TP_PROTO(const struct Qdisc_ops *ops, struct net_device *dev, u32 parent),
+
+	TP_ARGS(ops, dev, parent),
+
+	TP_STRUCT__entry(
+		__string(	dev,		dev->name	)
+		__string(	kind,		ops->id		)
+		__field(	u32,		parent		)
+	),
+
+	TP_fast_assign(
+		__assign_str(dev, dev->name);
+		__assign_str(kind, ops->id);
+		__entry->parent = parent;
+	),
+
+	TP_printk("dev=%s kind=%s parent=%x:%x",
+		  __get_str(dev), __get_str(kind),
+		  TC_H_MAJ(__entry->parent) >> 16, TC_H_MIN(__entry->parent))
+);
+
 #endif /* _TRACE_QDISC_H */
 
 /* This part must be outside protection */

net/sched/sch_api.c

@@ -32,6 +32,8 @@
 #include <net/pkt_sched.h>
 #include <net/pkt_cls.h>
 
+#include <trace/events/qdisc.h>
+
 /*
 
    Short review.
@@ -1283,6 +1285,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
 	}
 
 	qdisc_hash_add(sch, false);
+	trace_qdisc_create(ops, dev, parent);
 
 	return sch;
 

net/sched/sch_generic.c

@@ -896,8 +896,10 @@ struct Qdisc *qdisc_create_dflt(struct netdev_queue *dev_queue,
 	}
 	sch->parent = parentid;
 
-	if (!ops->init || ops->init(sch, NULL, extack) == 0)
+	if (!ops->init || ops->init(sch, NULL, extack) == 0) {
+		trace_qdisc_create(ops, dev_queue->dev, parentid);
 		return sch;
+	}
 
 	qdisc_put(sch);
 	return NULL;