[PATCH net-next 4/4] netem: add per-impairment extended statistics

Stephen Hemminger
2026-05-02T00:18:53Z

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.

Use the WRITE_ONCE/READ_ONCE pattern to allow for lockless
qdisc usage.

Accompanying iproute2 change is submitted separately.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
include/uapi/linux/pkt_sched.h | 9 ++++++++
net/sched/sch_netem.c | 40 +++++++++++++++++++++++++++++++---
2 files changed, 46 insertions(+), 3 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 116e96d79ddf..c871c7a3b117 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -152,6 +152,14 @@ struct netem_sched_data {
} slot;

struct disttable *slot_dist;
+
+ /* Per-impairment counters */
+ __u64 delayed;
+ __u64 dropped;
+ __u64 corrupted;
+ __u64 duplicated;
+ __u64 reordered;
+ __u64 ecn_marked;
};

/* Time stamp put into socket buffer control block
@@ -459,17 +467,23 @@ 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))
+ if (q->ecn && INET_ECN_set_ce(skb)) {
qdisc_qstats_drop(sch); /* mark packet */
- else
+ 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;
@@ -495,6 +509,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
* do it now in software before we mangle it.
*/
if (q->corrupt && q->corrupt >= get_crandom(&q->corrupt_cor, &q->prng)) {
+ WRITE_ONCE(q->corrupted, q->corrupted + 1);
if (skb_is_gso(skb)) {
skb = netem_segment(skb, sch, to_free);
if (!skb)
@@ -600,12 +615,15 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,

cb->time_to_send = now + delay;
++q->counter;
+ 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;

@@ -1344,6 +1362,21 @@ 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)
{
@@ -1406,6 +1439,7 @@ 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