[PATCH net-next 0/2] net/sched: sch_fq_pie: add per-flow class statistics

[PATCH net-next 0/2] net/sched: sch_fq_pie: add per-flow class statistics

[Hemendra M. Naik]

 FQ-PIE runs an independent PIE controller per flow but exposes no
 per-flow statistics. This series wires up fq_pie_class_ops to expose
 per-flow AQM state (prob, delay, deficit, avg_dq_rate) 
 via 'tc -s class show', following the same pattern as FQ-CoDel.

Hemendra M. Naik (2):
  net/sched: sch_fq_pie: add per-flow statistics via class ops
  selftests: tc-testing: add fq_pie per-flow class stats test

 include/uapi/linux/pkt_sched.h                |  29 +++-
 net/sched/sch_fq_pie.c                        | 131 ++++++++++++++++--
 tools/include/uapi/linux/pkt_sched.h          |   4 +-
 .../tc-testing/tc-tests/qdiscs/fq_pie.json    |  22 +++
 4 files changed, 168 insertions(+), 18 deletions(-)

-- 
2.34.1

[PATCH net-next 1/2] net/sched: sch_fq_pie: add per-flow statistics via class ops

[Hemendra M. Naik]

FQ-PIE schedules independent PIE controllers per flow but exposes no
per-flow AQM state. Without class-level statistics there is no way to
observe the per-flow drop probability, queue delay, deficit or 
dequeue rate from userspace.

Extend tc_fq_pie_xstats with a discriminated union, following the
same pattern established by FQ-CoDel (TCA_FQ_CODEL_XSTATS_CLASS):

  - Rename the existing flat struct to tc_fq_pie_qd_stats.
  - Add tc_fq_pie_cl_stats with per-flow prob, delay, deficit,
    avg_dq_rate, and dq_rate_estimating fields.
  - Wrap both in tc_fq_pie_xstats with a type discriminator
    (TCA_FQ_PIE_XSTATS_QDISC / TCA_FQ_PIE_XSTATS_CLASS).

Wire up fq_pie_class_ops (.walk, .dump, .dump_stats) so that
'tc -s class show' against an fq_pie qdisc reports per-flow state:

  prob               per-flow PIE drop probability
  delay              per-flow queue sojourn time (microseconds)
  deficit            remaining DRR byte credits (signed integer)
  avg_dq_rate        dequeue rate estimate in bytes/second
                     (dq_rate_estimator mode only)
  dq_rate_estimating flag indicating active delay estimation mode

Note: this changes the on-wire layout of tc_fq_pie_xstats. The type
field now occupies the first four bytes, displacing the former
packets_in field. Userspace must be updated concurrently; the
companion iproute2 patch handles this.

Fix the 'delay' field comment in struct tc_pie_xstats from "in ms" to
"in microseconds" to match the kernel's
PSCHED_TICKS2NS / NSEC_PER_USEC conversion.

Also correct the avg_dq_rate comment in tc_pie_xstats from
"bits/pie_time" to "bytes/second" to match the actual kernel
conversion (avg_dq_rate * PSCHED_TICKS_PER_SEC >> PIE_SCALE).

Signed-off-by: Hemendra M. Naik <hemendranaik@gmail.com>
Signed-off-by: Vishal Kamath <vishy0777@gmail.com>
Signed-off-by: Mohit P. Tahiliani <tahiliani@nitk.edu.in>
---
 include/uapi/linux/pkt_sched.h       |  29 +++++-
 net/sched/sch_fq_pie.c               | 131 ++++++++++++++++++++++++---
 tools/include/uapi/linux/pkt_sched.h |   4 +-
 3 files changed, 146 insertions(+), 18 deletions(-)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 66e8072f44df..0ad895edcb07 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -910,9 +910,9 @@ enum {
 
 struct tc_pie_xstats {
 	__u64 prob;			/* current probability */
-	__u32 delay;			/* current delay in ms */
+	__u32 delay;			/* current delay in microseconds */
 	__u32 avg_dq_rate;		/* current average dq_rate in
-					 * bits/pie_time
+					 * bytes/second
 					 */
 	__u32 dq_rate_estimating;	/* is avg_dq_rate being calculated? */
 	__u32 packets_in;		/* total number of packets enqueued */
@@ -943,7 +943,12 @@ enum {
 };
 #define TCA_FQ_PIE_MAX   (__TCA_FQ_PIE_MAX - 1)
 
-struct tc_fq_pie_xstats {
+enum {
+	TCA_FQ_PIE_XSTATS_QDISC,
+	TCA_FQ_PIE_XSTATS_CLASS,
+};
+
+struct tc_fq_pie_qd_stats {
 	__u32 packets_in;	/* total number of packets enqueued */
 	__u32 dropped;		/* packets dropped due to fq_pie_action */
 	__u32 overlimit;	/* dropped due to lack of space in queue */
@@ -955,6 +960,24 @@ struct tc_fq_pie_xstats {
 	__u32 memory_usage;	/* total memory across all queues */
 };
 
+struct tc_fq_pie_cl_stats {
+	__u64 prob;			/* current probability */
+	__u32 delay;			/* current delay in microseconds */
+	__s32 deficit;		/* number of remaining byte credits */
+	__u32 avg_dq_rate;		/* current average dq_rate in
+					 * bytes/second
+					 */
+	__u32 dq_rate_estimating;	/* is avg_dq_rate being calculated? */
+};
+
+struct tc_fq_pie_xstats {
+	__u32	type;
+	union {
+		struct tc_fq_pie_qd_stats qdisc_stats;
+		struct tc_fq_pie_cl_stats class_stats;
+	};
+};
+
 /* CBS */
 struct tc_cbs_qopt {
 	__u8 offload;
diff --git a/net/sched/sch_fq_pie.c b/net/sched/sch_fq_pie.c
index 7becbf5362b3..d22c4e02d2d9 100644
--- a/net/sched/sch_fq_pie.c
+++ b/net/sched/sch_fq_pie.c
@@ -330,7 +330,7 @@ static int fq_pie_change(struct Qdisc *sch, struct nlattr *opt,
 	/* tupdate is in jiffies */
 	if (tb[TCA_FQ_PIE_TUPDATE])
 		WRITE_ONCE(q->p_params.tupdate,
-			usecs_to_jiffies(nla_get_u32(tb[TCA_FQ_PIE_TUPDATE])));
+			   usecs_to_jiffies(nla_get_u32(tb[TCA_FQ_PIE_TUPDATE])));
 
 	if (tb[TCA_FQ_PIE_ALPHA])
 		WRITE_ONCE(q->p_params.alpha,
@@ -509,24 +509,25 @@ static int fq_pie_dump(struct Qdisc *sch, struct sk_buff *skb)
 static int fq_pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 {
 	struct fq_pie_sched_data *q = qdisc_priv(sch);
-	struct tc_fq_pie_xstats st = { 0 };
+	struct tc_fq_pie_xstats st = {
+		.type	= TCA_FQ_PIE_XSTATS_QDISC,
+	};
 	struct list_head *pos;
 
-	sch_tree_lock(sch);
-
-	st.packets_in	= q->stats.packets_in;
-	st.overlimit	= q->stats.overlimit;
-	st.overmemory	= q->overmemory;
-	st.dropped	= q->stats.dropped;
-	st.ecn_mark	= q->stats.ecn_mark;
-	st.new_flow_count = q->new_flow_count;
-	st.memory_usage   = q->memory_usage;
+	st.qdisc_stats.packets_in	= q->stats.packets_in;
+	st.qdisc_stats.overlimit	= q->stats.overlimit;
+	st.qdisc_stats.overmemory	= q->overmemory;
+	st.qdisc_stats.dropped		= q->stats.dropped;
+	st.qdisc_stats.ecn_mark		= q->stats.ecn_mark;
+	st.qdisc_stats.new_flow_count	= q->new_flow_count;
+	st.qdisc_stats.memory_usage	= q->memory_usage;
 
+	sch_tree_lock(sch);
 	list_for_each(pos, &q->new_flows)
-		st.new_flows_len++;
+		st.qdisc_stats.new_flows_len++;
 
 	list_for_each(pos, &q->old_flows)
-		st.old_flows_len++;
+		st.qdisc_stats.old_flows_len++;
 	sch_tree_unlock(sch);
 
 	return gnet_stats_copy_app(d, &st, sizeof(st));
@@ -561,7 +562,111 @@ static void fq_pie_destroy(struct Qdisc *sch)
 	kvfree(q->flows);
 }
 
+static struct Qdisc *fq_pie_leaf(struct Qdisc *sch, unsigned long arg)
+{
+	return NULL;
+}
+
+static unsigned long fq_pie_find(struct Qdisc *sch, u32 classid)
+{
+	return 0;
+}
+
+static unsigned long fq_pie_bind(struct Qdisc *sch, unsigned long parent,
+				 u32 classid)
+{
+	return 0;
+}
+
+static void fq_pie_unbind(struct Qdisc *q, unsigned long cl)
+{
+}
+
+static struct tcf_block *fq_pie_tcf_block(struct Qdisc *sch, unsigned long cl,
+					  struct netlink_ext_ack *extack)
+{
+	struct fq_pie_sched_data *q = qdisc_priv(sch);
+
+	if (cl)
+		return NULL;
+	return q->block;
+}
+
+static int fq_pie_dump_class(struct Qdisc *sch, unsigned long cl,
+			     struct sk_buff *skb, struct tcmsg *tcm)
+{
+	tcm->tcm_handle |= TC_H_MIN(cl);
+	return 0;
+}
+
+static int fq_pie_dump_class_stats(struct Qdisc *sch, unsigned long cl,
+				   struct gnet_dump *d)
+{
+	struct fq_pie_sched_data *q = qdisc_priv(sch);
+	struct gnet_stats_queue qs = { 0 };
+	struct tc_fq_pie_xstats xstats;
+	u32 idx = cl - 1;
+
+	if (idx < q->flows_cnt) {
+		const struct fq_pie_flow *flow = &q->flows[idx];
+
+		memset(&xstats, 0, sizeof(xstats));
+		xstats.type = TCA_FQ_PIE_XSTATS_CLASS;
+		xstats.class_stats.prob = READ_ONCE(flow->vars.prob) << BITS_PER_BYTE;
+		xstats.class_stats.delay =
+			((u32)PSCHED_TICKS2NS(READ_ONCE(flow->vars.qdelay))) /
+			NSEC_PER_USEC;
+		xstats.class_stats.deficit = READ_ONCE(flow->deficit);
+		xstats.class_stats.dq_rate_estimating =
+			READ_ONCE(q->p_params.dq_rate_estimator);
+
+		if (xstats.class_stats.dq_rate_estimating) {
+			xstats.class_stats.avg_dq_rate =
+				READ_ONCE(flow->vars.avg_dq_rate) *
+				(PSCHED_TICKS_PER_SEC) >> PIE_SCALE;
+		}
+
+		qs.qlen    = READ_ONCE(flow->qlen);
+		qs.backlog = READ_ONCE(flow->backlog);
+	}
+	if (gnet_stats_copy_queue(d, NULL, &qs, qs.qlen) < 0)
+		return -1;
+	if (idx < q->flows_cnt)
+		return gnet_stats_copy_app(d, &xstats, sizeof(xstats));
+	return 0;
+}
+
+static void fq_pie_walk(struct Qdisc *sch, struct qdisc_walker *arg)
+{
+	struct fq_pie_sched_data *q = qdisc_priv(sch);
+	unsigned int i;
+
+	if (arg->stop)
+		return;
+
+	for (i = 0; i < q->flows_cnt; i++) {
+		if (list_empty(&q->flows[i].flowchain)) {
+			arg->count++;
+			continue;
+		}
+		if (!tc_qdisc_stats_dump(sch, i + 1, arg))
+			break;
+	}
+}
+
+static const struct Qdisc_class_ops fq_pie_class_ops = {
+	.leaf		=	fq_pie_leaf,
+	.find		=	fq_pie_find,
+	.tcf_block	=	fq_pie_tcf_block,
+	.bind_tcf	=	fq_pie_bind,
+	.unbind_tcf	=	fq_pie_unbind,
+	.dump		=	fq_pie_dump_class,
+	.dump_stats	=	fq_pie_dump_class_stats,
+	.walk		=	fq_pie_walk,
+};
+
 static struct Qdisc_ops fq_pie_qdisc_ops __read_mostly = {
+	.cl_ops		=	&fq_pie_class_ops,
 	.id		= "fq_pie",
 	.priv_size	= sizeof(struct fq_pie_sched_data),
 	.enqueue	= fq_pie_qdisc_enqueue,
diff --git a/tools/include/uapi/linux/pkt_sched.h b/tools/include/uapi/linux/pkt_sched.h
index 587481a19433..9bc190f0b3cf 100644
--- a/tools/include/uapi/linux/pkt_sched.h
+++ b/tools/include/uapi/linux/pkt_sched.h
@@ -847,8 +847,8 @@ enum {
 
 struct tc_pie_xstats {
 	__u32 prob;             /* current probability */
-	__u32 delay;            /* current delay in ms */
-	__u32 avg_dq_rate;      /* current average dq_rate in bits/pie_time */
+	__u32 delay;            /* current delay in microseconds */
+	__u32 avg_dq_rate;      /* current average dq_rate in bytes/second */
 	__u32 packets_in;       /* total number of packets enqueued */
 	__u32 dropped;          /* packets dropped due to pie_action */
 	__u32 overlimit;        /* dropped due to lack of space in queue */
-- 
2.34.1

Re: [PATCH net-next 1/2] net/sched: sch_fq_pie: add per-flow statistics via class ops

[Stephen Hemminger]

On Sun, 31 May 2026 18:23:13 +0530
"Hemendra M. Naik" <hemendranaik@gmail.com> wrote:

> +struct tc_fq_pie_xstats {
> +	__u32	type;
> +	union {
> +		struct tc_fq_pie_qd_stats qdisc_stats;
> +		struct tc_fq_pie_cl_stats class_stats;
> +	};
> +};

Sorry, you can't change the kernel/userspace ABI like this.
How will old iproute2 hand new kernel and vice/versa.

The better safer way to do this is to either extend the
existing structure and have iproute2 know how how to handle
short (missing) class data; or use another netlink
type for class data.

Re: [PATCH net-next 1/2] net/sched: sch_fq_pie: add per-flow statistics via class ops

[Hemendra M. Naik]

On Sun, 31 May 2026 15:41:49 -0700, Stephen Hemminger wrote:

> Sorry, you can't change the kernel/userspace ABI like this.
> How will old iproute2 handle new kernel and vice/versa.
>
> The better safer way to do this is to either extend the
> existing structure and have iproute2 know how how to handle
> short (missing) class data; or use another netlink
> type for class data.

Hello Stephen,

Apologies for breaking the ABI.

We've been working on two fixes along the lines of what you suggested.

Approach #1

Append type and the union after the original 9 fields rather than
inserting them at the front:

struct tc_fq_pie_xstats {
__u32 packets_in;       /* offset  0, untouched */
...
__u32 memory_usage;     /* offset 32, untouched */
__u32 type;             /* offset 36, new */

```
      union {
              struct tc_fq_pie_cl_stats  class_stats;
              struct tc_fq_pie_xqd_stats xqdisc_stats;
      };
```

};

tc_fq_pie_xqd_stats is currently empty. It acts as a placeholder for
future qdisc stats if needed.

With this layout, older iproute2 versions receiving the new 64-byte
blob still see RTA_PAYLOAD(64) >= sizeof(36) and read the original
fields correctly since offsets 0-35 remain unchanged.

Conversely, newer iproute2 versions receiving the old 36-byte blob
take the memcpy path into a zeroed local struct, type defaults to 0
(QDISC), and execution falls back to the qdisc stats path.

Approach #2

Leave struct tc_fq_pie_xstats unchanged and export class stats
separately as an NLA blob via gnet_stats_copy_app():

enum {
TCA_FQ_PIE_XSTATS_UNSPEC,
TCA_FQ_PIE_XSTATS_TYPE,
TCA_FQ_PIE_XSTATS_CL_PROB,
TCA_FQ_PIE_XSTATS_CL_DELAY,
TCA_FQ_PIE_XSTATS_CL_AVG_DQ_RATE,
...
};

Adding any new stat, class or qdisc, is just a new enum entry and one
nla_put() call. Old iproute2 sees an unknown TYPE and skips it
gracefully via the default case. No struct versioning, no size math.

Let us know which approach you'd prefer, or if there's another
approach you think would work better, and we'll send a revised patch
accordingly.

Thanks,
Hemendra

[PATCH net-next 2/2] selftests: tc-testing: add fq_pie per-flow class stats test

[Hemendra M. Naik]

Add a tc-testing entry (id: 83c0) to verify the fq_pie class ops
wired up in the previous patch do not crash and integrate cleanly
with the tc class show path.

The test creates an fq_pie root qdisc on a dummy interface and runs
'tc -s class show'.

Signed-off-by: Hemendra M. Naik <hemendranaik@gmail.com>
Signed-off-by: Vishal Kamath <vishy0777@gmail.com>
Signed-off-by: Mohit P. Tahiliani <tahiliani@nitk.edu.in>
---
 .../tc-testing/tc-tests/qdiscs/fq_pie.json    | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/fq_pie.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/fq_pie.json
index 229fe1bf4a90..3ef2fafa52b8 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/fq_pie.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/fq_pie.json
@@ -40,5 +40,27 @@
         "matchPattern": "qdisc fq_pie 1: root refcnt [0-9]+ limit 1p",
         "matchCount": "1",
         "teardown": ["$TC qdisc del dev $DEV1 handle 1: root"]
+    },
+    {
+        "id": "83c0",
+        "name": "FQ-PIE class stats accessible via tc class show",
+        "category": [
+            "qdisc",
+            "fq_pie"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$TC qdisc add dev $DUMMY handle 1: root fq_pie"
+        ],
+        "cmdUnderTest": "$TC -s class show dev $DUMMY",
+        "expExitCode": "0",
+        "verifyCmd": "$TC -s class show dev $DUMMY",
+        "matchPattern": "class fq_pie",
+        "matchCount": "0",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
     }
 ]
-- 
2.34.1