[PATCH net-next v5 5/5] net/sched: netem: add per-impairment extended statistics
From: Stephen Hemminger
Date: Sat May 09 2026 - 13:12:21 EST
Add 64-bit counters for each impairment netem applies (delay, loss,
ECN marking, corruption, duplication, reordering) and for skb
allocation failures during enqueue. Exposed through TCA_STATS_APP
as struct tc_netem_xstats.
Counters increment when an impairment is occurs, independent of later
events that may mask its on-wire effect. Added allocation_errors
(similar to sch_fq) to account for when impairment could not be
applied due to memory pressure, etc.
Signed-off-by: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
---
Note to reviewers. The READ_ONCE/WRITE_ONCE pattern is to
align with upcoming changes removing qdisc_lock.
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 | 10 +++++++
net/sched/sch_netem.c | 55 ++++++++++++++++++++++++++++++----
2 files changed, 59 insertions(+), 6 deletions(-)
diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 66e8072f44df..490efd288526 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -569,6 +569,16 @@ 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)*/
+ __u64 allocation_errors;
+};
+
/* DRR */
enum {
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 699c734e4c8b..2433295c3920 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -152,6 +152,15 @@ struct netem_sched_data {
u8 state;
} clg;
+ /* Impairment counters */
+ u64 delayed;
+ u64 dropped;
+ u64 corrupted;
+ u64 duplicated;
+ u64 ecn_marked;
+ u64 reordered;
+ u64 allocation_errors;
+
/* Cold tail: slot reschedule config and the watchdog timer. */
struct tc_netem_slot slot_config;
struct qdisc_watchdog watchdog;
@@ -462,16 +471,21 @@ 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 */
- else
+ if (q->ecn && INET_ECN_set_ce(skb)) {
+ WRITE_ONCE(q->ecn_marked, q->ecn_marked + 1);
+ } else {
+ WRITE_ONCE(q->dropped, q->dropped + 1);
--count;
+ }
}
+
if (count == 0) {
qdisc_qstats_drop(sch);
__qdisc_drop(skb, to_free);
@@ -488,8 +502,11 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
* If we need to duplicate packet, then clone it before
* original is modified.
*/
- if (count > 1)
+ if (count > 1) {
skb2 = skb_clone(skb, GFP_ATOMIC);
+ if (!skb2)
+ WRITE_ONCE(q->allocation_errors, q->allocation_errors + 1);
+ }
/*
* Randomized packet corruption.
@@ -500,8 +517,10 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
if (q->corrupt && q->corrupt >= get_crandom(&q->corrupt_cor, &q->prng)) {
if (skb_is_gso(skb)) {
skb = netem_segment(skb, sch, to_free);
- if (!skb)
+ if (!skb) {
+ WRITE_ONCE(q->allocation_errors, q->allocation_errors + 1);
goto finish_segs;
+ }
segs = skb->next;
skb_mark_not_on_list(skb);
@@ -510,11 +529,13 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
skb = skb_unshare(skb, GFP_ATOMIC);
if (unlikely(!skb)) {
+ WRITE_ONCE(q->allocation_errors, q->allocation_errors + 1);
qdisc_qstats_drop(sch);
goto finish_segs;
}
if (skb_linearize(skb) ||
(skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_help(skb))) {
+ WRITE_ONCE(q->allocation_errors, q->allocation_errors + 1);
qdisc_drop(skb, sch, to_free);
skb = NULL;
goto finish_segs;
@@ -523,6 +544,7 @@ 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 +626,16 @@ 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;
@@ -1348,6 +1374,22 @@ 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),
+ .allocation_errors = READ_ONCE(q->allocation_errors),
+ };
+
+ 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)
{
@@ -1410,6 +1452,7 @@ 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