[PATCH v4 5/5] net/sched: netem: add per-impairment extended statistics

[Stephen Hemminger]

Adds new counters that keep track of when netem applied
impairments (delay, loss, corruption, duplication, reordering).
Add a struct tc_netem_xstats reported via TCA_STATS_APP so that
userspace (tc -s qdisc show) can display per-impairment counters.

The READ_ONCE/WRITE_ONCE pairing here matches the model used
elsewhere for xstats in the qdisc layer.

Also fixes a pre-existing accounting bug: ECN CE-marked packets
were being counted as drops (that is not what other qdisc's do).
Instead, now that there is a proper ecn_marked counter,
the spurious qdisc_qstats_drop() call can be removed.

Signed-off-by: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
---

Note to reviewers. The READ_ONCE/WRITE_ONCE pattern is allowed.
For some reason current AI prompts are obsessed with complaining
about 64 bit torn read/write on these, since the counters are
informational only, any such complaints are false positive.

Addition to iproute2 will be sent seperately.


 include/uapi/linux/pkt_sched.h |  9 +++++++++
 net/sched/sch_netem.c          | 37 ++++++++++++++++++++++++++++++++--
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 66e8072f44df..1c84c8076e22 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -569,6 +569,15 @@ struct tc_netem_gemodel {
 #define NETEM_DIST_SCALE	8192
 #define NETEM_DIST_MAX		16384
 
+struct tc_netem_xstats {
+	__u64	delayed;	/* packets delayed */
+	__u64	dropped;	/* packets dropped by loss model      */
+	__u64	corrupted;	/* packets with bit errors injected   */
+	__u64	duplicated;	/* duplicate packets generated        */
+	__u64	reordered;	/* packets sent out of order          */
+	__u64	ecn_marked;	/* packets ECN CE-marked (not dropped)*/
+};
+
 /* DRR */
 
 enum {
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 37df05bf43ee..6d8f4c4cedf3 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -152,6 +152,14 @@ struct netem_sched_data {
 		u8  state;
 	} clg;
 
+	/* Impairment counters */
+	u64			delayed;
+	u64			dropped;
+	u64			corrupted;
+	u64			duplicated;
+	u64			ecn_marked;
+	u64			reordered;
+
 	/* Cold tail: slot reschedule config and the watchdog timer. */
 	struct tc_netem_slot	slot_config;
 	struct qdisc_watchdog	watchdog;
@@ -462,17 +470,21 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	skb->prev = NULL;
 
 	/* Random duplication */
-	if (q->duplicate && q->duplicate >= get_crandom(&q->dup_cor, &q->prng))
+	if (q->duplicate && q->duplicate >= get_crandom(&q->dup_cor, &q->prng)) {
 		++count;
+		WRITE_ONCE(q->duplicated, q->duplicated + 1);
+	}
 
 	/* Drop packet? */
 	if (loss_event(q)) {
 		if (q->ecn && INET_ECN_set_ce(skb))
-			qdisc_qstats_drop(sch); /* mark packet */
+			WRITE_ONCE(q->ecn_marked, q->ecn_marked + 1);
 		else
 			--count;
 	}
+
 	if (count == 0) {
+		WRITE_ONCE(q->dropped, q->dropped + 1);
 		qdisc_qstats_drop(sch);
 		__qdisc_drop(skb, to_free);
 		return NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
@@ -523,6 +535,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		if (skb->len) {
 			u32 offset = get_random_u32_below(skb->len);
 			skb->data[offset] ^= 1 << get_random_u32_below(8);
+			WRITE_ONCE(q->corrupted, q->corrupted + 1);
 		}
 	}
 
@@ -604,12 +617,16 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 
 		cb->time_to_send = now + delay;
 		++q->counter;
+		if (delay)
+			WRITE_ONCE(q->delayed, q->delayed + 1);
+
 		tfifo_enqueue(skb, sch);
 	} else {
 		/*
 		 * Do re-ordering by putting one out of N packets at the front
 		 * of the queue.
 		 */
+		WRITE_ONCE(q->reordered, q->reordered + 1);
 		cb->time_to_send = ktime_get_ns();
 		q->counter = 0;
 
@@ -1350,6 +1367,21 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff *skb)
 	return -1;
 }
 
+static int netem_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
+{
+	struct netem_sched_data *q = qdisc_priv(sch);
+	struct tc_netem_xstats st = {
+		.delayed    = READ_ONCE(q->delayed),
+		.dropped    = READ_ONCE(q->dropped),
+		.corrupted  = READ_ONCE(q->corrupted),
+		.duplicated = READ_ONCE(q->duplicated),
+		.reordered  = READ_ONCE(q->reordered),
+		.ecn_marked = READ_ONCE(q->ecn_marked),
+	};
+
+	return gnet_stats_copy_app(d, &st, sizeof(st));
+}
+
 static int netem_dump_class(struct Qdisc *sch, unsigned long cl,
 			  struct sk_buff *skb, struct tcmsg *tcm)
 {
@@ -1412,6 +1444,7 @@ static struct Qdisc_ops netem_qdisc_ops __read_mostly = {
 	.destroy	=	netem_destroy,
 	.change		=	netem_change,
 	.dump		=	netem_dump,
+	.dump_stats	=	netem_dump_stats,
 	.owner		=	THIS_MODULE,
 };
 MODULE_ALIAS_NET_SCH("netem");
-- 
2.53.0