[net-next 1/2] qdisc: add tracepoint qdisc:qdisc_enqueue for enqueued SKBs

[xiangxia.m.yue@gmail.com]

From: Tonghao Zhang <xiangxia.m.yue@gmail.com>

This tracepoint can work with qdisc:qdisc_dequeue to measure
packets latency in qdisc queue. In some case, for example,
if TX queues are stopped or frozen, sch_direct_xmit will invoke
the dev_requeue_skb to requeue SKBs to qdisc->gso_skb, that may
delay the SKBs in qdisc queue.

With this patch, we can measure packets latency.

Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
---
 include/net/pkt_sched.h      |  4 ++++
 include/trace/events/qdisc.h | 32 ++++++++++++++++++++++++++++++++
 net/core/dev.c               |  4 ++--
 net/sched/sch_generic.c      | 11 +++++++++++
 4 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 6d7b12cba015..66411b4ff284 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -133,6 +133,10 @@ static inline void qdisc_run(struct Qdisc *q)
 	}
 }
 
+int qdisc_enqueue_skb(struct netdev_queue *txq, struct Qdisc *q,
+		      struct sk_buff *skb,
+		      struct sk_buff **to_free);
+
 /* Calculate maximal size of packet seen by hard_start_xmit
    routine of this device.
  */
diff --git a/include/trace/events/qdisc.h b/include/trace/events/qdisc.h
index 330d32d84485..b0e76237bb74 100644
--- a/include/trace/events/qdisc.h
+++ b/include/trace/events/qdisc.h
@@ -11,6 +11,38 @@
 #include <linux/pkt_sched.h>
 #include <net/sch_generic.h>
 
+TRACE_EVENT(qdisc_enqueue,
+
+	TP_PROTO(struct Qdisc *qdisc, const struct netdev_queue *txq,
+		 struct sk_buff *skb, int ret),
+
+	TP_ARGS(qdisc, txq, skb, ret),
+
+	TP_STRUCT__entry(
+		__field(	struct Qdisc *,		qdisc	)
+		__field(const	struct netdev_queue *,	txq	)
+		__field(	void *,			skbaddr	)
+		__field(	int,			ifindex	)
+		__field(	u32,			handle	)
+		__field(	u32,			parent	)
+		__field(	int,			ret	)
+	),
+
+	TP_fast_assign(
+		__entry->qdisc		= qdisc;
+		__entry->txq		= txq;
+		__entry->skbaddr	= skb;
+		__entry->ifindex	= txq->dev ? txq->dev->ifindex : 0;
+		__entry->handle		= qdisc->handle;
+		__entry->parent		= qdisc->parent;
+		__entry->ret		= ret;
+	),
+
+	TP_printk("enqueue ifindex=%d qdisc handle=0x%X parent=0x%X skbaddr=%p ret=%d",
+		  __entry->ifindex, __entry->handle, __entry->parent,
+		  __entry->skbaddr, __entry->ret)
+);
+
 TRACE_EVENT(qdisc_dequeue,
 
 	TP_PROTO(struct Qdisc *qdisc, const struct netdev_queue *txq,
diff --git a/net/core/dev.c b/net/core/dev.c
index 50531a2d0b20..78efac6b2e60 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3852,7 +3852,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
 	qdisc_calculate_pkt_len(skb, q);
 
 	if (q->flags & TCQ_F_NOLOCK) {
-		rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
+		rc = qdisc_enqueue_skb(txq, q, skb, &to_free);
 		if (likely(!netif_xmit_frozen_or_stopped(txq)))
 			qdisc_run(q);
 
@@ -3896,7 +3896,7 @@ 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 = qdisc_enqueue_skb(txq, q, skb, &to_free);
 		if (qdisc_run_begin(q)) {
 			if (unlikely(contended)) {
 				spin_unlock(&q->busylock);
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index e9c0afc8becc..75605075178f 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -415,6 +415,17 @@ void __qdisc_run(struct Qdisc *q)
 	}
 }
 
+int qdisc_enqueue_skb(struct netdev_queue *txq, struct Qdisc *q,
+		      struct sk_buff *skb,
+		      struct sk_buff **to_free)
+{
+	int ret;
+
+	ret = q->enqueue(skb, q, to_free) & NET_XMIT_MASK;
+	trace_qdisc_enqueue(q, txq, skb, ret);
+	return ret;
+}
+
 unsigned long dev_trans_start(struct net_device *dev)
 {
 	unsigned long val, res;
-- 
2.27.0