[PATCH net-next v6 0/3] net/sched: sch_fq_pie: add per-flow class statistics

[PATCH net-next v6 0/3] 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 a similar pattern as FQ-CoDel.

This patch series is accompanied by a companion iproute2 patch series that
can be found at:
https://lore.kernel.org/netdev/20260902040221.83734-1-hemendranaik@gmail.com/

---
Changelog:

v6:
- Address Sashiko review comments:
  - Revert the fq_pie flows range to [1..65536]. 
  - Also drop the accompanying selftest 83be change.
  - Compute the per-flow delay with div_u64() on the full 64-bit
    nanosecond value.
  - Widen avg_dq_rate to u64 before scaling it by PSCHED_TICKS_PER_SEC.
  - Document the 36 to 64 byte xstats growth in the patch 1 commit message.
  - Fix selftest 83c0. The ping payload exceeded the TBF burst so no
    packet ever reached fq_pie, and the missing -W left the run waiting
    out ping's default timeout.

v5: https://lore.kernel.org/netdev/20260902035231.81866-1-hemendranaik@gmail.com/
- Addressed Sashiko review comments:
 - Omitted .tcf_block / .bind_tcf / .unbind_tcf from cl_ops (statistics
   only being exported; filter attach to fq_pie is now disabled).
 - Dropped empty tc_fq_pie_xqd_stats placeholder; class_stats is a direct
   struct member.
 - Limited flows to [1..65535] so per-flow class handles fit in a 16-bit
   TC minor.
 - Rewrote selftest 83c0 with TBF + fq_pie, ping traffic, and
   matchCount 1 on per-flow stats output.
 - Updated selftest 83be for the new flows limit.
 - Dropped the tools/include UAPI mirror changes from patch 3/3.

v4: https://lore.kernel.org/netdev/20260727164056.106203-1-hemendranaik@gmail.com/
- Fixed unaligned commit message; moved typo fixes to another patch.

v3: https://lore.kernel.org/netdev/20260630183702.170798-1-hemendranaik@gmail.com/
- No changes since v2.
- Resent after the previous submission was deferred due to the
  net-next tree closing during review.
- Updated corresponding iproute2 patch in response to review comments;
  kernel patches unchanged.

v2: https://lore.kernel.org/netdev/20260614125000.6058-1-hemendranaik@gmail.com/
- Addressed ABI backward compatibility issue for tc_fq_pie_xstats.

v1: https://lore.kernel.org/netdev/20260531125314.22492-1-hemendranaik@gmail.com/
- Initial submission

Hemendra M. Naik (3):
  net/sched: sch_fq_pie: add per-flow statistics via class ops
  selftests: tc-testing: add fq_pie per-flow class stats test
  net/sched: pie: correct tc_pie_xstats field documentation

 include/uapi/linux/pkt_sched.h                | 20 ++++-
 net/sched/sch_fq_pie.c                        | 86 ++++++++++++++++++-
 .../tc-testing/tc-tests/qdiscs/fq_pie.json    | 27 ++++++
 3 files changed, 130 insertions(+), 3 deletions(-)

-- 
2.34.1

[PATCH net-next v6 1/3] 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 type discriminator and tc_fq_pie_cl_stats
for per-flow metrics. The nine existing __u32 counters keep their
offsets, type is appended at offset 36 and class_stats follows it,
growing the structure from 36 to 64 bytes.

Wire up fq_pie_class_ops with walk, dump, and dump_stats only so that
'tc -s class show' reports per-flow state (prob, delay, deficit,
avg_dq_rate, dq_rate_estimating). Filter attachment callbacks
(.tcf_block, .bind_tcf, .unbind_tcf) are omitted on purpose.

Derive delay with div_u64() from the full 64-bit nanosecond value rather
than truncating to u32 before dividing, which wrapped for sojourn times
above ~4.295 s, and widen avg_dq_rate to u64 before scaling it by
PSCHED_TICKS_PER_SEC.

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 | 16 +++++++
 net/sched/sch_fq_pie.c         | 86 +++++++++++++++++++++++++++++++++-
 2 files changed, 101 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 490efd288526..9c0c9787f0c3 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -953,6 +953,20 @@ enum {
 };
 #define TCA_FQ_PIE_MAX   (__TCA_FQ_PIE_MAX - 1)
 
+enum {
+	TCA_FQ_PIE_XSTATS_QDISC,
+	TCA_FQ_PIE_XSTATS_CLASS,
+};
+
+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 packets_in;	/* total number of packets enqueued */
 	__u32 dropped;		/* packets dropped due to fq_pie_action */
@@ -963,6 +977,8 @@ struct tc_fq_pie_xstats {
 	__u32 new_flows_len;	/* count of flows in new list */
 	__u32 old_flows_len;	/* count of flows in old list */
 	__u32 memory_usage;	/* total memory across all queues */
+	__u32 type;
+	struct tc_fq_pie_cl_stats class_stats;
 };
 
 /* CBS */
diff --git a/net/sched/sch_fq_pie.c b/net/sched/sch_fq_pie.c
index 5982847df8f8..675861f578b8 100644
--- a/net/sched/sch_fq_pie.c
+++ b/net/sched/sch_fq_pie.c
@@ -511,7 +511,9 @@ 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);
@@ -563,7 +565,89 @@ 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 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 =
+			div_u64(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 =
+				((u64)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,
+	.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,
-- 
2.34.1

[PATCH net-next v6 2/3] selftests: tc-testing: add fq_pie per-flow class stats test

[Hemendra M. Naik]

Add tc-testing case 83c0: build a TBF + fq_pie hierarchy on $DUMMY, push
traffic through it with ping, and verify that 'tc -s class show' reports
an fq_pie class.

The per-flow counters themselves (prob, delay, deficit) are printed only
after the companion iproute2 change, "tc: fq_pie: add support for printing
per-flow PIE statistics"

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    | 27 +++++++++++++++++++
 1 file changed, 27 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..15b2667285eb 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 +40,32 @@
         "matchPattern": "qdisc fq_pie 1: root refcnt [0-9]+ limit 1p",
         "matchCount": "1",
         "teardown": ["$TC qdisc del dev $DEV1 handle 1: root"]
+    },
+    {
+        "id": "83c0",
+        "name": "FQ-PIE class stats accessible via tc class show",
+        "category": [
+            "qdisc",
+            "fq_pie"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$IP link set dev $DUMMY up || true",
+            "$IP addr add 10.10.11.10/24 dev $DUMMY || true",
+            "$TC qdisc add dev $DUMMY root handle 1: tbf rate 8bit burst 100b latency 100ms",
+            "$TC qdisc add dev $DUMMY parent 1:1 handle 2: fq_pie limit 100 flows 1",
+            "ping -c 50 -i 0.001 -W 0.01 -s 56 10.10.11.11 -I $DUMMY > /dev/null 2>&1 || true"
+        ],
+        "cmdUnderTest": "$TC -s class show dev $DUMMY",
+        "expExitCode": "0",
+        "verifyCmd": "$TC -s class show dev $DUMMY",
+        "matchPattern": "class fq_pie 2:[0-9]+ .*prob .*delay .*deficit",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root",
+            "$IP addr del 10.10.11.10/24 dev $DUMMY || true"
+        ]
     }
 ]
-- 
2.34.1

[PATCH net-next v6 3/3] net/sched: pie: correct tc_pie_xstats field documentation

[Hemendra M. Naik]

The comments describing struct tc_pie_xstats do not match the values
exported by the kernel.

Update the delay field comment to microseconds (PSCHED_TICKS2NS() /
NSEC_PER_USEC). Update avg_dq_rate to bytes/second (avg_dq_rate *
PSCHED_TICKS_PER_SEC >> PIE_SCALE).

Documentation-only; no UAPI layout or runtime change. Touch
include/uapi/linux/pkt_sched.h only

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 | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 9c0c9787f0c3..969fa30efae7 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -920,9 +920,9 @@ 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 */
-- 
2.34.1

Re: [PATCH net-next v6 0/3] net/sched: sch_fq_pie: add per-flow class statistics

[Jakub Kicinski]

On Fri, 18 Sep 2026 02:12:22 +0530 Hemendra M. Naik wrote:
> This patch series is accompanied by a companion iproute2 patch series that
> can be found at:
> https://lore.kernel.org/netdev/20260902040221.83734-1-hemendranaik@gmail.com/

Does not apply any more. Also can you put it on a branch on github to
make it easier to pull please ? 

Please rebase and repost both the kernel and the iproute2. 

Re: [PATCH net-next v6 0/3] net/sched: sch_fq_pie: add per-flow class statistics

[Hemendra M. Naik]

Hi Jakub,

We've posted the new patches for kernel (v7) and iproute2 (v6) 
after rebasing.

The mailing list threads can be tracked here:
- Kernel v7: https://lore.kernel.org/netdev/20260919060125.38063-1-hemendranaik@gmail.com/
- iproute2 v6: https://lore.kernel.org/netdev/20260919061254.39678-1-hemendranaik@gmail.com/

As requested, we have also posted the latest 
patches on GitHub which can be found here:

- https://github.com/H-N41K/linux-net-next/tree/fq_pie_class_stats/
- https://github.com/H-N41K/iproute2-next/tree/fq_pie_class_stats/

Thanks,
Hemendra