Merge branch 'dualpi2-patch'

Chia-Yu Chang says:

====================
DUALPI2 patch

This patch serise adds DualPI Improved with a Square (DualPI2) with
following features:
* Supports congestion controls that comply with the Prague requirements
in RFC9331 (e.g. TCP-Prague)
* Coupled dual-queue that separates the L4S traffic in a low latency
queue (L-queue), without harming remaining traffic that is scheduled
in classic queue (C-queue) due to congestion-coupling using PI2
as defined in RFC9332
* Configurable overload strategies
* Use of sojourn time to reliably estimate queue delay
* Supports ECN L4S-identifier (IP.ECN==0b*1) to classify traffic into
respective queues

For more details of DualPI2, please refer IETF RFC9332
(https://datatracker.ietf.org/doc/html/rfc9332).
====================

Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/netlink/specs/tc.yaml

···
       - tunoam
       - tuncrit
   -
+    name: dualpi2-drop-overload
+    type: enum
+    entries: [overflow, drop]
+  -
+    name: dualpi2-drop-early
+    type: enum
+    entries: [drop-dequeue, drop-enqueue]
+  -
+    name: dualpi2-ecn-mask
+    type: enum
+    value-start: 1
+    entries: [l4s-ect, cla-ect, any-ect]
+  -
+    name: dualpi2-split-gso
+    type: enum
+    entries: [no-split-gso, split-gso]
+  -
     name: tc-stats
     type: struct
     members:
···
         name: drop-overmemory
         type: u32
   -
+    name: tc-dualpi2-xstats
+    type: struct
+    members:
+      -
+        name: prob
+        type: u32
+        doc: Current base PI probability
+      -
+        name: delay-c
+        type: u32
+        doc: Current C-queue delay in microseconds
+      -
+        name: delay-l
+        type: u32
+        doc: Current L-queue delay in microseconds
+      -
+        name: pkts-in-c
+        type: u32
+        doc: Number of packets enqueued in the C-queue
+      -
+        name: pkts-in-l
+        type: u32
+        doc: Number of packets enqueued in the L-queue
+      -
+        name: maxq
+        type: u32
+        doc: Maximum number of packets seen by the DualPI2
+      -
+        name: ecn-mark
+        type: u32
+        doc: All packets marked with ECN
+      -
+        name: step-mark
+        type: u32
+        doc: Only packets marked with ECN due to L-queue step AQM
+      -
+        name: credit
+        type: s32
+        doc: Current credit value for WRR
+      -
+        name: memory-used
+        type: u32
+        doc: Memory used in bytes by the DualPI2
+      -
+        name: max-memory-used
+        type: u32
+        doc: Maximum memory used in bytes by the DualPI2
+      -
+        name: memory-limit
+        type: u32
+        doc: Memory limit in bytes
+  -
     name: tc-fq-pie-xstats
     type: struct
     members:
···
       -
         name: ecn-mark
         type: u32
-        doc: Packets marked with ecn
+        doc: Packets marked with ECN
       -
         name: new-flow-count
         type: u32
···
       -
         name: ecn-mark
         type: u32
-        doc: Packets marked with ecn
+        doc: Packets marked with ECN
   -
     name: tc-red-xstats
     type: struct
···
       -
         name: quantum
         type: u32
+  -
+    name: dualpi2-attrs
+    name-prefix: tca-dualpi2-
+    attributes:
+      -
+        name: limit
+        type: u32
+        doc: Limit of total number of packets in queue
+      -
+        name: memory-limit
+        type: u32
+        doc: Memory limit of total number of packets in queue
+      -
+        name: target
+        type: u32
+        doc: Classic target delay in microseconds
+      -
+        name: tupdate
+        type: u32
+        doc: Drop probability update interval time in microseconds
+      -
+        name: alpha
+        type: u32
+        doc: Integral gain factor in Hz for PI controller
+      -
+        name: beta
+        type: u32
+        doc: Proportional gain factor in Hz for PI controller
+      -
+        name: step-thresh-pkts
+        type: u32
+        doc: L4S step marking threshold in packets
+      -
+        name: step-thresh-us
+        type: u32
+        doc: L4S Step marking threshold in microseconds
+      -
+        name: min-qlen-step
+        type: u32
+        doc: Packets enqueued to the L-queue can apply the step threshold
+             when the queue length of L-queue is larger than this value.
+             (0 is recommended)
+      -
+        name: coupling
+        type: u8
+        doc: Probability coupling factor between Classic and L4S
+             (2 is recommended)
+      -
+        name: drop-overload
+        type: u8
+        doc: Control the overload strategy (drop to preserve latency or
+             let the queue overflow)
+        enum: dualpi2-drop-overload
+      -
+        name: drop-early
+        type: u8
+        doc: Decide where the Classic packets are PI-based dropped or marked
+        enum: dualpi2-drop-early
+      -
+        name: c-protection
+        type: u8
+        doc: Classic WRR weight in percentage (from 0 to 100)
+      -
+        name: ecn-mask
+        type: u8
+        doc: Configure the L-queue ECN classifier
+        enum: dualpi2-ecn-mask
+      -
+        name: split-gso
+        type: u8
+        doc: Split aggregated skb or not
+        enum: dualpi2-split-gso
   -
     name: ematch-attrs
     name-prefix: tca-ematch-
···
         value: drr
         attribute-set: drr-attrs
       -
+        value: dualpi2
+        attribute-set: dualpi2-attrs
+      -
         value: etf
         attribute-set: etf-attrs
       -
···
       -
         value: codel
         fixed-header: tc-codel-xstats
+      -
+        value: dualpi2
+        fixed-header: tc-dualpi2-xstats
       -
         value: fq
         fixed-header: tc-fq-qd-stats

include/net/dropreason-core.h

···
 	FN(CANFD_RX_INVALID_FRAME)	\
 	FN(CANXL_RX_INVALID_FRAME)	\
 	FN(PFMEMALLOC)	\
+	FN(DUALPI2_STEP_DROP)		\
 	FNe(MAX)
 
 /**
···
 	 * reached a path or socket not eligible for use of memory reserves
 	 */
 	SKB_DROP_REASON_PFMEMALLOC,
+	/**
+	 * @SKB_DROP_REASON_DUALPI2_STEP_DROP: dropped by the step drop
+	 * threshold of DualPI2 qdisc.
+	 */
+	SKB_DROP_REASON_DUALPI2_STEP_DROP,
 	/**
 	 * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
 	 * shouldn't be used as a real 'reason' - only for tracing code gen

include/uapi/linux/pkt_sched.h

···
 
 #define TCA_ETS_MAX (__TCA_ETS_MAX - 1)
 
+/* DUALPI2 */
+enum tc_dualpi2_drop_overload {
+	TC_DUALPI2_DROP_OVERLOAD_OVERFLOW = 0,
+	TC_DUALPI2_DROP_OVERLOAD_DROP = 1,
+	__TCA_DUALPI2_DROP_OVERLOAD_MAX,
+};
+#define TCA_DUALPI2_DROP_OVERLOAD_MAX (__TCA_DUALPI2_DROP_OVERLOAD_MAX - 1)
+
+enum tc_dualpi2_drop_early {
+	TC_DUALPI2_DROP_EARLY_DROP_DEQUEUE = 0,
+	TC_DUALPI2_DROP_EARLY_DROP_ENQUEUE = 1,
+	__TCA_DUALPI2_DROP_EARLY_MAX,
+};
+#define TCA_DUALPI2_DROP_EARLY_MAX (__TCA_DUALPI2_DROP_EARLY_MAX - 1)
+
+enum tc_dualpi2_ecn_mask {
+	TC_DUALPI2_ECN_MASK_L4S_ECT = 1,
+	TC_DUALPI2_ECN_MASK_CLA_ECT = 2,
+	TC_DUALPI2_ECN_MASK_ANY_ECT = 3,
+	__TCA_DUALPI2_ECN_MASK_MAX,
+};
+#define TCA_DUALPI2_ECN_MASK_MAX (__TCA_DUALPI2_ECN_MASK_MAX - 1)
+
+enum tc_dualpi2_split_gso {
+	TC_DUALPI2_SPLIT_GSO_NO_SPLIT_GSO = 0,
+	TC_DUALPI2_SPLIT_GSO_SPLIT_GSO = 1,
+	__TCA_DUALPI2_SPLIT_GSO_MAX,
+};
+#define TCA_DUALPI2_SPLIT_GSO_MAX (__TCA_DUALPI2_SPLIT_GSO_MAX - 1)
+
+enum {
+	TCA_DUALPI2_UNSPEC,
+	TCA_DUALPI2_LIMIT,		/* Packets */
+	TCA_DUALPI2_MEMORY_LIMIT,	/* Bytes */
+	TCA_DUALPI2_TARGET,		/* us */
+	TCA_DUALPI2_TUPDATE,		/* us */
+	TCA_DUALPI2_ALPHA,		/* Hz scaled up by 256 */
+	TCA_DUALPI2_BETA,		/* Hz scaled up by 256 */
+	TCA_DUALPI2_STEP_THRESH_PKTS,	/* Step threshold in packets */
+	TCA_DUALPI2_STEP_THRESH_US,	/* Step threshold in microseconds */
+	TCA_DUALPI2_MIN_QLEN_STEP,	/* Minimum qlen to apply STEP_THRESH */
+	TCA_DUALPI2_COUPLING,		/* Coupling factor between queues */
+	TCA_DUALPI2_DROP_OVERLOAD,	/* Whether to drop on overload */
+	TCA_DUALPI2_DROP_EARLY,		/* Whether to drop on enqueue */
+	TCA_DUALPI2_C_PROTECTION,	/* Percentage */
+	TCA_DUALPI2_ECN_MASK,		/* L4S queue classification mask */
+	TCA_DUALPI2_SPLIT_GSO,		/* Split GSO packets at enqueue */
+	TCA_DUALPI2_PAD,
+	__TCA_DUALPI2_MAX
+};
+
+#define TCA_DUALPI2_MAX   (__TCA_DUALPI2_MAX - 1)
+
+struct tc_dualpi2_xstats {
+	__u32 prob;		/* current probability */
+	__u32 delay_c;		/* current delay in C queue */
+	__u32 delay_l;		/* current delay in L queue */
+	__u32 packets_in_c;	/* number of packets enqueued in C queue */
+	__u32 packets_in_l;	/* number of packets enqueued in L queue */
+	__u32 maxq;		/* maximum queue size */
+	__u32 ecn_mark;		/* packets marked with ecn*/
+	__u32 step_marks;	/* ECN marks due to the step AQM */
+	__s32 credit;		/* current c_protection credit */
+	__u32 memory_used;	/* Memory used by both queues */
+	__u32 max_memory_used;	/* Maximum used memory */
+	__u32 memory_limit;	/* Memory limit of both queues */
+};
+
 #endif

net/sched/Kconfig

···
 
 	  If unsure, say N.
 
+config NET_SCH_DUALPI2
+	tristate "Dual Queue PI Square (DUALPI2) scheduler"
+	help
+	  Say Y here if you want to use the Dual Queue Proportional Integral
+	  Controller Improved with a Square scheduling algorithm.
+	  For more information, please see https://tools.ietf.org/html/rfc9332
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called sch_dualpi2.
+
+	  If unsure, say N.
+
 menuconfig NET_SCH_DEFAULT
 	bool "Allow override default queue discipline"
 	help

net/sched/Makefile

···
 obj-$(CONFIG_NET_SCH_ETF)	+= sch_etf.o
 obj-$(CONFIG_NET_SCH_TAPRIO)	+= sch_taprio.o
 obj-$(CONFIG_NET_SCH_BPF)	+= bpf_qdisc.o
+obj-$(CONFIG_NET_SCH_DUALPI2)	+= sch_dualpi2.o
 
 obj-$(CONFIG_NET_CLS_U32)	+= cls_u32.o
 obj-$(CONFIG_NET_CLS_ROUTE4)	+= cls_route.o

net/sched/sch_dualpi2.c

···
+// SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+/* Copyright (C) 2024 Nokia
+ *
+ * Author: Koen De Schepper <[e-mail]>
+ * Author: Olga Albisser <[e-mail]>
+ * Author: Henrik Steen <[e-mail]>
+ * Author: Olivier Tilmans <[e-mail]>
+ * Author: Chia-Yu Chang <[e-mail]>
+ *
+ * DualPI Improved with a Square (dualpi2):
+ * - Supports congestion controls that comply with the Prague requirements
+ *   in RFC9331 (e.g. TCP-Prague)
+ * - Supports coupled dual-queue with PI2 as defined in RFC9332
+ * - Supports ECN L4S-identifier (IP.ECN==0b*1)
+ *
+ * note: Although DCTCP and BBRv3 can use shallow-threshold ECN marks,
+ *   they do not meet the 'Prague L4S Requirements' listed in RFC 9331
+ *   Section 4, so they can only be used with DualPI2 in a datacenter
+ *   context.
+ *
+ * References:
+ * - RFC9332: https://datatracker.ietf.org/doc/html/rfc9332
+ * - De Schepper, Koen, et al. "PI 2: A linearized AQM for both classic and
+ *   scalable TCP."  in proc. ACM CoNEXT'16, 2016.
+ */
+
+#include <linux/errno.h>
+#include <linux/hrtimer.h>
+#include <linux/if_vlan.h>
+#include <linux/kernel.h>
+#include <linux/limits.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/types.h>
+
+#include <net/gso.h>
+#include <net/inet_ecn.h>
+#include <net/pkt_cls.h>
+#include <net/pkt_sched.h>
+
+/* 32b enable to support flows with windows up to ~8.6 * 1e9 packets
+ * i.e., twice the maximal snd_cwnd.
+ * MAX_PROB must be consistent with the RNG in dualpi2_roll().
+ */
+#define MAX_PROB U32_MAX
+
+/* alpha/beta values exchanged over netlink are in units of 256ns */
+#define ALPHA_BETA_SHIFT 8
+
+/* Scaled values of alpha/beta must fit in 32b to avoid overflow in later
+ * computations. Consequently (see and dualpi2_scale_alpha_beta()), their
+ * netlink-provided values can use at most 31b, i.e. be at most (2^23)-1
+ * (~4MHz) as those are given in 1/256th. This enable to tune alpha/beta to
+ * control flows whose maximal RTTs can be in usec up to few secs.
+ */
+#define ALPHA_BETA_MAX ((1U << 31) - 1)
+
+/* Internal alpha/beta are in units of 64ns.
+ * This enables to use all alpha/beta values in the allowed range without loss
+ * of precision due to rounding when scaling them internally, e.g.,
+ * scale_alpha_beta(1) will not round down to 0.
+ */
+#define ALPHA_BETA_GRANULARITY 6
+
+#define ALPHA_BETA_SCALING (ALPHA_BETA_SHIFT - ALPHA_BETA_GRANULARITY)
+
+/* We express the weights (wc, wl) in %, i.e., wc + wl = 100 */
+#define MAX_WC 100
+
+struct dualpi2_sched_data {
+	struct Qdisc *l_queue;	/* The L4S Low latency queue (L-queue) */
+	struct Qdisc *sch;	/* The Classic queue (C-queue) */
+
+	/* Registered tc filters */
+	struct tcf_proto __rcu *tcf_filters;
+	struct tcf_block *tcf_block;
+
+	/* PI2 parameters */
+	u64	pi2_target;	/* Target delay in nanoseconds */
+	u32	pi2_tupdate;	/* Timer frequency in nanoseconds */
+	u32	pi2_prob;	/* Base PI probability */
+	u32	pi2_alpha;	/* Gain factor for the integral rate response */
+	u32	pi2_beta;	/* Gain factor for the proportional response */
+	struct hrtimer pi2_timer; /* prob update timer */
+
+	/* Step AQM (L-queue only) parameters */
+	u32	step_thresh;	/* Step threshold */
+	bool	step_in_packets; /* Step thresh in packets (1) or time (0) */
+
+	/* C-queue starvation protection */
+	s32	c_protection_credit; /* Credit (sign indicates which queue) */
+	s32	c_protection_init; /* Reset value of the credit */
+	u8	c_protection_wc; /* C-queue weight (between 0 and MAX_WC) */
+	u8	c_protection_wl; /* L-queue weight (MAX_WC - wc) */
+
+	/* General dualQ parameters */
+	u32	memory_limit;	/* Memory limit of both queues */
+	u8	coupling_factor;/* Coupling factor (k) between both queues */
+	u8	ecn_mask;	/* Mask to match packets into L-queue */
+	u32	min_qlen_step;	/* Minimum queue length to apply step thresh */
+	bool	drop_early;	/* Drop at enqueue (1) instead of dequeue  (0) */
+	bool	drop_overload;	/* Drop (1) on overload, or overflow (0) */
+	bool	split_gso;	/* Split aggregated skb (1) or leave as is (0) */
+
+	/* Statistics */
+	u64	c_head_ts;	/* Enqueue timestamp of the C-queue head */
+	u64	l_head_ts;	/* Enqueue timestamp of the L-queue head */
+	u64	last_qdelay;	/* Q delay val at the last probability update */
+	u32	packets_in_c;	/* Enqueue packet counter of the C-queue */
+	u32	packets_in_l;	/* Enqueue packet counter of the L-queue */
+	u32	maxq;		/* Maximum queue size of the C-queue */
+	u32	ecn_mark;	/* ECN mark pkt counter due to PI probability */
+	u32	step_marks;	/* ECN mark pkt counter due to step AQM */
+	u32	memory_used;	/* Memory used of both queues */
+	u32	max_memory_used;/* Maximum used memory */
+
+	/* Deferred drop statistics */
+	u32	deferred_drops_cnt;	/* Packets dropped */
+	u32	deferred_drops_len;	/* Bytes dropped */
+};
+
+struct dualpi2_skb_cb {
+	u64 ts;			/* Timestamp at enqueue */
+	u8 apply_step:1,	/* Can we apply the step threshold */
+	   classified:2,	/* Packet classification results */
+	   ect:2;		/* Packet ECT codepoint */
+};
+
+enum dualpi2_classification_results {
+	DUALPI2_C_CLASSIC	= 0,	/* C-queue */
+	DUALPI2_C_L4S		= 1,	/* L-queue (scale mark/classic drop) */
+	DUALPI2_C_LLLL		= 2,	/* L-queue (no drops/marks) */
+	__DUALPI2_C_MAX			/* Keep last*/
+};
+
+static struct dualpi2_skb_cb *dualpi2_skb_cb(struct sk_buff *skb)
+{
+	qdisc_cb_private_validate(skb, sizeof(struct dualpi2_skb_cb));
+	return (struct dualpi2_skb_cb *)qdisc_skb_cb(skb)->data;
+}
+
+static u64 dualpi2_sojourn_time(struct sk_buff *skb, u64 reference)
+{
+	return reference - dualpi2_skb_cb(skb)->ts;
+}
+
+static u64 head_enqueue_time(struct Qdisc *q)
+{
+	struct sk_buff *skb = qdisc_peek_head(q);
+
+	return skb ? dualpi2_skb_cb(skb)->ts : 0;
+}
+
+static u32 dualpi2_scale_alpha_beta(u32 param)
+{
+	u64 tmp = ((u64)param * MAX_PROB >> ALPHA_BETA_SCALING);
+
+	do_div(tmp, NSEC_PER_SEC);
+	return tmp;
+}
+
+static u32 dualpi2_unscale_alpha_beta(u32 param)
+{
+	u64 tmp = ((u64)param * NSEC_PER_SEC << ALPHA_BETA_SCALING);
+
+	do_div(tmp, MAX_PROB);
+	return tmp;
+}
+
+static ktime_t next_pi2_timeout(struct dualpi2_sched_data *q)
+{
+	return ktime_add_ns(ktime_get_ns(), q->pi2_tupdate);
+}
+
+static bool skb_is_l4s(struct sk_buff *skb)
+{
+	return dualpi2_skb_cb(skb)->classified == DUALPI2_C_L4S;
+}
+
+static bool skb_in_l_queue(struct sk_buff *skb)
+{
+	return dualpi2_skb_cb(skb)->classified != DUALPI2_C_CLASSIC;
+}
+
+static bool skb_apply_step(struct sk_buff *skb, struct dualpi2_sched_data *q)
+{
+	return skb_is_l4s(skb) && qdisc_qlen(q->l_queue) >= q->min_qlen_step;
+}
+
+static bool dualpi2_mark(struct dualpi2_sched_data *q, struct sk_buff *skb)
+{
+	if (INET_ECN_set_ce(skb)) {
+		q->ecn_mark++;
+		return true;
+	}
+	return false;
+}
+
+static void dualpi2_reset_c_protection(struct dualpi2_sched_data *q)
+{
+	q->c_protection_credit = q->c_protection_init;
+}
+
+/* This computes the initial credit value and WRR weight for the L queue (wl)
+ * from the weight of the C queue (wc).
+ * If wl > wc, the scheduler will start with the L queue when reset.
+ */
+static void dualpi2_calculate_c_protection(struct Qdisc *sch,
+					   struct dualpi2_sched_data *q, u32 wc)
+{
+	q->c_protection_wc = wc;
+	q->c_protection_wl = MAX_WC - wc;
+	q->c_protection_init = (s32)psched_mtu(qdisc_dev(sch)) *
+		((int)q->c_protection_wc - (int)q->c_protection_wl);
+	dualpi2_reset_c_protection(q);
+}
+
+static bool dualpi2_roll(u32 prob)
+{
+	return get_random_u32() <= prob;
+}
+
+/* Packets in the C-queue are subject to a marking probability pC, which is the
+ * square of the internal PI probability (i.e., have an overall lower mark/drop
+ * probability). If the qdisc is overloaded, ignore ECT values and only drop.
+ *
+ * Note that this marking scheme is also applied to L4S packets during overload.
+ * Return true if packet dropping is required in C queue
+ */
+static bool dualpi2_classic_marking(struct dualpi2_sched_data *q,
+				    struct sk_buff *skb, u32 prob,
+				    bool overload)
+{
+	if (dualpi2_roll(prob) && dualpi2_roll(prob)) {
+		if (overload || dualpi2_skb_cb(skb)->ect == INET_ECN_NOT_ECT)
+			return true;
+		dualpi2_mark(q, skb);
+	}
+	return false;
+}
+
+/* Packets in the L-queue are subject to a marking probability pL given by the
+ * internal PI probability scaled by the coupling factor.
+ *
+ * On overload (i.e., @local_l_prob is >= 100%):
+ * - if the qdisc is configured to trade losses to preserve latency (i.e.,
+ *   @q->drop_overload), apply classic drops first before marking.
+ * - otherwise, preserve the "no loss" property of ECN at the cost of queueing
+ *   delay, eventually resulting in taildrop behavior once sch->limit is
+ *   reached.
+ * Return true if packet dropping is required in L queue
+ */
+static bool dualpi2_scalable_marking(struct dualpi2_sched_data *q,
+				     struct sk_buff *skb,
+				     u64 local_l_prob, u32 prob,
+				     bool overload)
+{
+	if (overload) {
+		/* Apply classic drop */
+		if (!q->drop_overload ||
+		    !(dualpi2_roll(prob) && dualpi2_roll(prob)))
+			goto mark;
+		return true;
+	}
+
+	/* We can safely cut the upper 32b as overload==false */
+	if (dualpi2_roll(local_l_prob)) {
+		/* Non-ECT packets could have classified as L4S by filters. */
+		if (dualpi2_skb_cb(skb)->ect == INET_ECN_NOT_ECT)
+			return true;
+mark:
+		dualpi2_mark(q, skb);
+	}
+	return false;
+}
+
+/* Decide whether a given packet must be dropped (or marked if ECT), according
+ * to the PI2 probability.
+ *
+ * Never mark/drop if we have a standing queue of less than 2 MTUs.
+ */
+static bool must_drop(struct Qdisc *sch, struct dualpi2_sched_data *q,
+		      struct sk_buff *skb)
+{
+	u64 local_l_prob;
+	bool overload;
+	u32 prob;
+
+	if (sch->qstats.backlog < 2 * psched_mtu(qdisc_dev(sch)))
+		return false;
+
+	prob = READ_ONCE(q->pi2_prob);
+	local_l_prob = (u64)prob * q->coupling_factor;
+	overload = local_l_prob > MAX_PROB;
+
+	switch (dualpi2_skb_cb(skb)->classified) {
+	case DUALPI2_C_CLASSIC:
+		return dualpi2_classic_marking(q, skb, prob, overload);
+	case DUALPI2_C_L4S:
+		return dualpi2_scalable_marking(q, skb, local_l_prob, prob,
+						overload);
+	default: /* DUALPI2_C_LLLL */
+		return false;
+	}
+}
+
+static void dualpi2_read_ect(struct sk_buff *skb)
+{
+	struct dualpi2_skb_cb *cb = dualpi2_skb_cb(skb);
+	int wlen = skb_network_offset(skb);
+
+	switch (skb_protocol(skb, true)) {
+	case htons(ETH_P_IP):
+		wlen += sizeof(struct iphdr);
+		if (!pskb_may_pull(skb, wlen) ||
+		    skb_try_make_writable(skb, wlen))
+			goto not_ecn;
+
+		cb->ect = ipv4_get_dsfield(ip_hdr(skb)) & INET_ECN_MASK;
+		break;
+	case htons(ETH_P_IPV6):
+		wlen += sizeof(struct ipv6hdr);
+		if (!pskb_may_pull(skb, wlen) ||
+		    skb_try_make_writable(skb, wlen))
+			goto not_ecn;
+
+		cb->ect = ipv6_get_dsfield(ipv6_hdr(skb)) & INET_ECN_MASK;
+		break;
+	default:
+		goto not_ecn;
+	}
+	return;
+
+not_ecn:
+	/* Non pullable/writable packets can only be dropped hence are
+	 * classified as not ECT.
+	 */
+	cb->ect = INET_ECN_NOT_ECT;
+}
+
+static int dualpi2_skb_classify(struct dualpi2_sched_data *q,
+				struct sk_buff *skb)
+{
+	struct dualpi2_skb_cb *cb = dualpi2_skb_cb(skb);
+	struct tcf_result res;
+	struct tcf_proto *fl;
+	int result;
+
+	dualpi2_read_ect(skb);
+	if (cb->ect & q->ecn_mask) {
+		cb->classified = DUALPI2_C_L4S;
+		return NET_XMIT_SUCCESS;
+	}
+
+	if (TC_H_MAJ(skb->priority) == q->sch->handle &&
+	    TC_H_MIN(skb->priority) < __DUALPI2_C_MAX) {
+		cb->classified = TC_H_MIN(skb->priority);
+		return NET_XMIT_SUCCESS;
+	}
+
+	fl = rcu_dereference_bh(q->tcf_filters);
+	if (!fl) {
+		cb->classified = DUALPI2_C_CLASSIC;
+		return NET_XMIT_SUCCESS;
+	}
+
+	result = tcf_classify(skb, NULL, fl, &res, false);
+	if (result >= 0) {
+#ifdef CONFIG_NET_CLS_ACT
+		switch (result) {
+		case TC_ACT_STOLEN:
+		case TC_ACT_QUEUED:
+		case TC_ACT_TRAP:
+			return NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
+		case TC_ACT_SHOT:
+			return NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
+		}
+#endif
+		cb->classified = TC_H_MIN(res.classid) < __DUALPI2_C_MAX ?
+			TC_H_MIN(res.classid) : DUALPI2_C_CLASSIC;
+	}
+	return NET_XMIT_SUCCESS;
+}
+
+static int dualpi2_enqueue_skb(struct sk_buff *skb, struct Qdisc *sch,
+			       struct sk_buff **to_free)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+	struct dualpi2_skb_cb *cb;
+
+	if (unlikely(qdisc_qlen(sch) >= sch->limit) ||
+	    unlikely((u64)q->memory_used + skb->truesize > q->memory_limit)) {
+		qdisc_qstats_overlimit(sch);
+		if (skb_in_l_queue(skb))
+			qdisc_qstats_overlimit(q->l_queue);
+		return qdisc_drop_reason(skb, sch, to_free,
+					 SKB_DROP_REASON_QDISC_OVERLIMIT);
+	}
+
+	if (q->drop_early && must_drop(sch, q, skb)) {
+		qdisc_drop_reason(skb, sch, to_free,
+				  SKB_DROP_REASON_QDISC_CONGESTED);
+		return NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
+	}
+
+	cb = dualpi2_skb_cb(skb);
+	cb->ts = ktime_get_ns();
+	q->memory_used += skb->truesize;
+	if (q->memory_used > q->max_memory_used)
+		q->max_memory_used = q->memory_used;
+
+	if (qdisc_qlen(sch) > q->maxq)
+		q->maxq = qdisc_qlen(sch);
+
+	if (skb_in_l_queue(skb)) {
+		/* Apply step thresh if skb is L4S && L-queue len >= min_qlen */
+		dualpi2_skb_cb(skb)->apply_step = skb_apply_step(skb, q);
+
+		/* Keep the overall qdisc stats consistent */
+		++sch->q.qlen;
+		qdisc_qstats_backlog_inc(sch, skb);
+		++q->packets_in_l;
+		if (!q->l_head_ts)
+			q->l_head_ts = cb->ts;
+		return qdisc_enqueue_tail(skb, q->l_queue);
+	}
+	++q->packets_in_c;
+	if (!q->c_head_ts)
+		q->c_head_ts = cb->ts;
+	return qdisc_enqueue_tail(skb, sch);
+}
+
+/* By default, dualpi2 will split GSO skbs into independent skbs and enqueue
+ * each of those individually. This yields the following benefits, at the
+ * expense of CPU usage:
+ * - Finer-grained AQM actions as the sub-packets of a burst no longer share the
+ *   same fate (e.g., the random mark/drop probability is applied individually)
+ * - Improved precision of the starvation protection/WRR scheduler at dequeue,
+ *   as the size of the dequeued packets will be smaller.
+ */
+static int dualpi2_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
+				 struct sk_buff **to_free)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+	int err;
+
+	err = dualpi2_skb_classify(q, skb);
+	if (err != NET_XMIT_SUCCESS) {
+		if (err & __NET_XMIT_BYPASS)
+			qdisc_qstats_drop(sch);
+		__qdisc_drop(skb, to_free);
+		return err;
+	}
+
+	if (q->split_gso && skb_is_gso(skb)) {
+		netdev_features_t features;
+		struct sk_buff *nskb, *next;
+		int cnt, byte_len, orig_len;
+		int err;
+
+		features = netif_skb_features(skb);
+		nskb = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);
+		if (IS_ERR_OR_NULL(nskb))
+			return qdisc_drop(skb, sch, to_free);
+
+		cnt = 1;
+		byte_len = 0;
+		orig_len = qdisc_pkt_len(skb);
+		skb_list_walk_safe(nskb, nskb, next) {
+			skb_mark_not_on_list(nskb);
+
+			/* Iterate through GSO fragments of an skb:
+			 * (1) Set pkt_len from the single GSO fragments
+			 * (2) Copy classified and ect values of an skb
+			 * (3) Enqueue fragment & set ts in dualpi2_enqueue_skb
+			 */
+			qdisc_skb_cb(nskb)->pkt_len = nskb->len;
+			dualpi2_skb_cb(nskb)->classified =
+				dualpi2_skb_cb(skb)->classified;
+			dualpi2_skb_cb(nskb)->ect = dualpi2_skb_cb(skb)->ect;
+			err = dualpi2_enqueue_skb(nskb, sch, to_free);
+
+			if (err == NET_XMIT_SUCCESS) {
+				/* Compute the backlog adjustment that needs
+				 * to be propagated in the qdisc tree to reflect
+				 * all new skbs successfully enqueued.
+				 */
+				++cnt;
+				byte_len += nskb->len;
+			}
+		}
+		if (cnt > 1) {
+			/* The caller will add the original skb stats to its
+			 * backlog, compensate this if any nskb is enqueued.
+			 */
+			--cnt;
+			byte_len -= orig_len;
+		}
+		qdisc_tree_reduce_backlog(sch, -cnt, -byte_len);
+		consume_skb(skb);
+		return err;
+	}
+	return dualpi2_enqueue_skb(skb, sch, to_free);
+}
+
+/* Select the queue from which the next packet can be dequeued, ensuring that
+ * neither queue can starve the other with a WRR scheduler.
+ *
+ * The sign of the WRR credit determines the next queue, while the size of
+ * the dequeued packet determines the magnitude of the WRR credit change. If
+ * either queue is empty, the WRR credit is kept unchanged.
+ *
+ * As the dequeued packet can be dropped later, the caller has to perform the
+ * qdisc_bstats_update() calls.
+ */
+static struct sk_buff *dequeue_packet(struct Qdisc *sch,
+				      struct dualpi2_sched_data *q,
+				      int *credit_change,
+				      u64 now)
+{
+	struct sk_buff *skb = NULL;
+	int c_len;
+
+	*credit_change = 0;
+	c_len = qdisc_qlen(sch) - qdisc_qlen(q->l_queue);
+	if (qdisc_qlen(q->l_queue) && (!c_len || q->c_protection_credit <= 0)) {
+		skb = __qdisc_dequeue_head(&q->l_queue->q);
+		WRITE_ONCE(q->l_head_ts, head_enqueue_time(q->l_queue));
+		if (c_len)
+			*credit_change = q->c_protection_wc;
+		qdisc_qstats_backlog_dec(q->l_queue, skb);
+
+		/* Keep the global queue size consistent */
+		--sch->q.qlen;
+		q->memory_used -= skb->truesize;
+	} else if (c_len) {
+		skb = __qdisc_dequeue_head(&sch->q);
+		WRITE_ONCE(q->c_head_ts, head_enqueue_time(sch));
+		if (qdisc_qlen(q->l_queue))
+			*credit_change = ~((s32)q->c_protection_wl) + 1;
+		q->memory_used -= skb->truesize;
+	} else {
+		dualpi2_reset_c_protection(q);
+		return NULL;
+	}
+	*credit_change *= qdisc_pkt_len(skb);
+	qdisc_qstats_backlog_dec(sch, skb);
+	return skb;
+}
+
+static int do_step_aqm(struct dualpi2_sched_data *q, struct sk_buff *skb,
+		       u64 now)
+{
+	u64 qdelay = 0;
+
+	if (q->step_in_packets)
+		qdelay = qdisc_qlen(q->l_queue);
+	else
+		qdelay = dualpi2_sojourn_time(skb, now);
+
+	if (dualpi2_skb_cb(skb)->apply_step && qdelay > q->step_thresh) {
+		if (!dualpi2_skb_cb(skb)->ect) {
+			/* Drop this non-ECT packet */
+			return 1;
+		}
+
+		if (dualpi2_mark(q, skb))
+			++q->step_marks;
+	}
+	qdisc_bstats_update(q->l_queue, skb);
+	return 0;
+}
+
+static void drop_and_retry(struct dualpi2_sched_data *q, struct sk_buff *skb,
+			   struct Qdisc *sch, enum skb_drop_reason reason)
+{
+	++q->deferred_drops_cnt;
+	q->deferred_drops_len += qdisc_pkt_len(skb);
+	kfree_skb_reason(skb, reason);
+	qdisc_qstats_drop(sch);
+}
+
+static struct sk_buff *dualpi2_qdisc_dequeue(struct Qdisc *sch)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+	struct sk_buff *skb;
+	int credit_change;
+	u64 now;
+
+	now = ktime_get_ns();
+
+	while ((skb = dequeue_packet(sch, q, &credit_change, now))) {
+		if (!q->drop_early && must_drop(sch, q, skb)) {
+			drop_and_retry(q, skb, sch,
+				       SKB_DROP_REASON_QDISC_CONGESTED);
+			continue;
+		}
+
+		if (skb_in_l_queue(skb) && do_step_aqm(q, skb, now)) {
+			qdisc_qstats_drop(q->l_queue);
+			drop_and_retry(q, skb, sch,
+				       SKB_DROP_REASON_DUALPI2_STEP_DROP);
+			continue;
+		}
+
+		q->c_protection_credit += credit_change;
+		qdisc_bstats_update(sch, skb);
+		break;
+	}
+
+	if (q->deferred_drops_cnt) {
+		qdisc_tree_reduce_backlog(sch, q->deferred_drops_cnt,
+					  q->deferred_drops_len);
+		q->deferred_drops_cnt = 0;
+		q->deferred_drops_len = 0;
+	}
+	return skb;
+}
+
+static s64 __scale_delta(u64 diff)
+{
+	do_div(diff, 1 << ALPHA_BETA_GRANULARITY);
+	return diff;
+}
+
+static void get_queue_delays(struct dualpi2_sched_data *q, u64 *qdelay_c,
+			     u64 *qdelay_l)
+{
+	u64 now, qc, ql;
+
+	now = ktime_get_ns();
+	qc = READ_ONCE(q->c_head_ts);
+	ql = READ_ONCE(q->l_head_ts);
+
+	*qdelay_c = qc ? now - qc : 0;
+	*qdelay_l = ql ? now - ql : 0;
+}
+
+static u32 calculate_probability(struct Qdisc *sch)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+	u32 new_prob;
+	u64 qdelay_c;
+	u64 qdelay_l;
+	u64 qdelay;
+	s64 delta;
+
+	get_queue_delays(q, &qdelay_c, &qdelay_l);
+	qdelay = max(qdelay_l, qdelay_c);
+
+	/* Alpha and beta take at most 32b, i.e, the delay difference would
+	 * overflow for queuing delay differences > ~4.2sec.
+	 */
+	delta = ((s64)qdelay - (s64)q->pi2_target) * q->pi2_alpha;
+	delta += ((s64)qdelay - (s64)q->last_qdelay) * q->pi2_beta;
+	q->last_qdelay = qdelay;
+
+	/* Bound new_prob between 0 and MAX_PROB */
+	if (delta > 0) {
+		new_prob = __scale_delta(delta) + q->pi2_prob;
+		if (new_prob < q->pi2_prob)
+			new_prob = MAX_PROB;
+	} else {
+		new_prob = q->pi2_prob - __scale_delta(~delta + 1);
+		if (new_prob > q->pi2_prob)
+			new_prob = 0;
+	}
+
+	/* If we do not drop on overload, ensure we cap the L4S probability to
+	 * 100% to keep window fairness when overflowing.
+	 */
+	if (!q->drop_overload)
+		return min_t(u32, new_prob, MAX_PROB / q->coupling_factor);
+	return new_prob;
+}
+
+static u32 get_memory_limit(struct Qdisc *sch, u32 limit)
+{
+	/* Apply rule of thumb, i.e., doubling the packet length,
+	 * to further include per packet overhead in memory_limit.
+	 */
+	u64 memlim = mul_u32_u32(limit, 2 * psched_mtu(qdisc_dev(sch)));
+
+	if (upper_32_bits(memlim))
+		return U32_MAX;
+	else
+		return lower_32_bits(memlim);
+}
+
+static u32 convert_us_to_nsec(u32 us)
+{
+	u64 ns = mul_u32_u32(us, NSEC_PER_USEC);
+
+	if (upper_32_bits(ns))
+		return U32_MAX;
+
+	return lower_32_bits(ns);
+}
+
+static u32 convert_ns_to_usec(u64 ns)
+{
+	do_div(ns, NSEC_PER_USEC);
+	if (upper_32_bits(ns))
+		return U32_MAX;
+
+	return lower_32_bits(ns);
+}
+
+static enum hrtimer_restart dualpi2_timer(struct hrtimer *timer)
+{
+	struct dualpi2_sched_data *q = timer_container_of(q, timer, pi2_timer);
+	struct Qdisc *sch = q->sch;
+	spinlock_t *root_lock; /* to lock qdisc for probability calculations */
+
+	rcu_read_lock();
+	root_lock = qdisc_lock(qdisc_root_sleeping(sch));
+	spin_lock(root_lock);
+
+	WRITE_ONCE(q->pi2_prob, calculate_probability(sch));
+	hrtimer_set_expires(&q->pi2_timer, next_pi2_timeout(q));
+
+	spin_unlock(root_lock);
+	rcu_read_unlock();
+	return HRTIMER_RESTART;
+}
+
+static struct netlink_range_validation dualpi2_alpha_beta_range = {
+	.min = 1,
+	.max = ALPHA_BETA_MAX,
+};
+
+static const struct nla_policy dualpi2_policy[TCA_DUALPI2_MAX + 1] = {
+	[TCA_DUALPI2_LIMIT]		= NLA_POLICY_MIN(NLA_U32, 1),
+	[TCA_DUALPI2_MEMORY_LIMIT]	= NLA_POLICY_MIN(NLA_U32, 1),
+	[TCA_DUALPI2_TARGET]		= { .type = NLA_U32 },
+	[TCA_DUALPI2_TUPDATE]		= NLA_POLICY_MIN(NLA_U32, 1),
+	[TCA_DUALPI2_ALPHA]		=
+		NLA_POLICY_FULL_RANGE(NLA_U32, &dualpi2_alpha_beta_range),
+	[TCA_DUALPI2_BETA]		=
+		NLA_POLICY_FULL_RANGE(NLA_U32, &dualpi2_alpha_beta_range),
+	[TCA_DUALPI2_STEP_THRESH_PKTS]	= { .type = NLA_U32 },
+	[TCA_DUALPI2_STEP_THRESH_US]	= { .type = NLA_U32 },
+	[TCA_DUALPI2_MIN_QLEN_STEP]	= { .type = NLA_U32 },
+	[TCA_DUALPI2_COUPLING]		= NLA_POLICY_MIN(NLA_U8, 1),
+	[TCA_DUALPI2_DROP_OVERLOAD]	=
+		NLA_POLICY_MAX(NLA_U8, TCA_DUALPI2_DROP_OVERLOAD_MAX),
+	[TCA_DUALPI2_DROP_EARLY]	=
+		NLA_POLICY_MAX(NLA_U8, TCA_DUALPI2_DROP_EARLY_MAX),
+	[TCA_DUALPI2_C_PROTECTION]	=
+		NLA_POLICY_RANGE(NLA_U8, 0, MAX_WC),
+	[TCA_DUALPI2_ECN_MASK]		=
+		NLA_POLICY_RANGE(NLA_U8, TC_DUALPI2_ECN_MASK_L4S_ECT,
+				 TCA_DUALPI2_ECN_MASK_MAX),
+	[TCA_DUALPI2_SPLIT_GSO]		=
+		NLA_POLICY_MAX(NLA_U8, TCA_DUALPI2_SPLIT_GSO_MAX),
+};
+
+static int dualpi2_change(struct Qdisc *sch, struct nlattr *opt,
+			  struct netlink_ext_ack *extack)
+{
+	struct nlattr *tb[TCA_DUALPI2_MAX + 1];
+	struct dualpi2_sched_data *q;
+	int old_backlog;
+	int old_qlen;
+	int err;
+
+	if (!opt || !nla_len(opt)) {
+		NL_SET_ERR_MSG_MOD(extack, "Dualpi2 options are required");
+		return -EINVAL;
+	}
+	err = nla_parse_nested(tb, TCA_DUALPI2_MAX, opt, dualpi2_policy,
+			       extack);
+	if (err < 0)
+		return err;
+	if (tb[TCA_DUALPI2_STEP_THRESH_PKTS] && tb[TCA_DUALPI2_STEP_THRESH_US]) {
+		NL_SET_ERR_MSG_MOD(extack, "multiple step thresh attributes");
+		return -EINVAL;
+	}
+
+	q = qdisc_priv(sch);
+	sch_tree_lock(sch);
+
+	if (tb[TCA_DUALPI2_LIMIT]) {
+		u32 limit = nla_get_u32(tb[TCA_DUALPI2_LIMIT]);
+
+		WRITE_ONCE(sch->limit, limit);
+		WRITE_ONCE(q->memory_limit, get_memory_limit(sch, limit));
+	}
+
+	if (tb[TCA_DUALPI2_MEMORY_LIMIT])
+		WRITE_ONCE(q->memory_limit,
+			   nla_get_u32(tb[TCA_DUALPI2_MEMORY_LIMIT]));
+
+	if (tb[TCA_DUALPI2_TARGET]) {
+		u64 target = nla_get_u32(tb[TCA_DUALPI2_TARGET]);
+
+		WRITE_ONCE(q->pi2_target, target * NSEC_PER_USEC);
+	}
+
+	if (tb[TCA_DUALPI2_TUPDATE]) {
+		u64 tupdate = nla_get_u32(tb[TCA_DUALPI2_TUPDATE]);
+
+		WRITE_ONCE(q->pi2_tupdate, convert_us_to_nsec(tupdate));
+	}
+
+	if (tb[TCA_DUALPI2_ALPHA]) {
+		u32 alpha = nla_get_u32(tb[TCA_DUALPI2_ALPHA]);
+
+		WRITE_ONCE(q->pi2_alpha, dualpi2_scale_alpha_beta(alpha));
+	}
+
+	if (tb[TCA_DUALPI2_BETA]) {
+		u32 beta = nla_get_u32(tb[TCA_DUALPI2_BETA]);
+
+		WRITE_ONCE(q->pi2_beta, dualpi2_scale_alpha_beta(beta));
+	}
+
+	if (tb[TCA_DUALPI2_STEP_THRESH_PKTS]) {
+		u32 step_th = nla_get_u32(tb[TCA_DUALPI2_STEP_THRESH_PKTS]);
+
+		WRITE_ONCE(q->step_in_packets, true);
+		WRITE_ONCE(q->step_thresh, step_th);
+	} else if (tb[TCA_DUALPI2_STEP_THRESH_US]) {
+		u32 step_th = nla_get_u32(tb[TCA_DUALPI2_STEP_THRESH_US]);
+
+		WRITE_ONCE(q->step_in_packets, false);
+		WRITE_ONCE(q->step_thresh, convert_us_to_nsec(step_th));
+	}
+
+	if (tb[TCA_DUALPI2_MIN_QLEN_STEP])
+		WRITE_ONCE(q->min_qlen_step,
+			   nla_get_u32(tb[TCA_DUALPI2_MIN_QLEN_STEP]));
+
+	if (tb[TCA_DUALPI2_COUPLING]) {
+		u8 coupling = nla_get_u8(tb[TCA_DUALPI2_COUPLING]);
+
+		WRITE_ONCE(q->coupling_factor, coupling);
+	}
+
+	if (tb[TCA_DUALPI2_DROP_OVERLOAD]) {
+		u8 drop_overload = nla_get_u8(tb[TCA_DUALPI2_DROP_OVERLOAD]);
+
+		WRITE_ONCE(q->drop_overload, (bool)drop_overload);
+	}
+
+	if (tb[TCA_DUALPI2_DROP_EARLY]) {
+		u8 drop_early = nla_get_u8(tb[TCA_DUALPI2_DROP_EARLY]);
+
+		WRITE_ONCE(q->drop_early, (bool)drop_early);
+	}
+
+	if (tb[TCA_DUALPI2_C_PROTECTION]) {
+		u8 wc = nla_get_u8(tb[TCA_DUALPI2_C_PROTECTION]);
+
+		dualpi2_calculate_c_protection(sch, q, wc);
+	}
+
+	if (tb[TCA_DUALPI2_ECN_MASK]) {
+		u8 ecn_mask = nla_get_u8(tb[TCA_DUALPI2_ECN_MASK]);
+
+		WRITE_ONCE(q->ecn_mask, ecn_mask);
+	}
+
+	if (tb[TCA_DUALPI2_SPLIT_GSO]) {
+		u8 split_gso = nla_get_u8(tb[TCA_DUALPI2_SPLIT_GSO]);
+
+		WRITE_ONCE(q->split_gso, (bool)split_gso);
+	}
+
+	old_qlen = qdisc_qlen(sch);
+	old_backlog = sch->qstats.backlog;
+	while (qdisc_qlen(sch) > sch->limit ||
+	       q->memory_used > q->memory_limit) {
+		struct sk_buff *skb = qdisc_dequeue_internal(sch, true);
+
+		q->memory_used -= skb->truesize;
+		qdisc_qstats_backlog_dec(sch, skb);
+		rtnl_qdisc_drop(skb, sch);
+	}
+	qdisc_tree_reduce_backlog(sch, old_qlen - qdisc_qlen(sch),
+				  old_backlog - sch->qstats.backlog);
+
+	sch_tree_unlock(sch);
+	return 0;
+}
+
+/* Default alpha/beta values give a 10dB stability margin with max_rtt=100ms. */
+static void dualpi2_reset_default(struct Qdisc *sch)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+
+	q->sch->limit = 10000;				/* Max 125ms at 1Gbps */
+	q->memory_limit = get_memory_limit(sch, q->sch->limit);
+
+	q->pi2_target = 15 * NSEC_PER_MSEC;
+	q->pi2_tupdate = 16 * NSEC_PER_MSEC;
+	q->pi2_alpha = dualpi2_scale_alpha_beta(41);	/* ~0.16 Hz * 256 */
+	q->pi2_beta = dualpi2_scale_alpha_beta(819);	/* ~3.20 Hz * 256 */
+
+	q->step_thresh = 1 * NSEC_PER_MSEC;
+	q->step_in_packets = false;
+
+	dualpi2_calculate_c_protection(q->sch, q, 10);	/* wc=10%, wl=90% */
+
+	q->ecn_mask = TC_DUALPI2_ECN_MASK_L4S_ECT;	/* INET_ECN_ECT_1 */
+	q->min_qlen_step = 0;		/* Always apply step mark in L-queue */
+	q->coupling_factor = 2;		/* window fairness for equal RTTs */
+	q->drop_overload = TC_DUALPI2_DROP_OVERLOAD_DROP; /* Drop overload */
+	q->drop_early = TC_DUALPI2_DROP_EARLY_DROP_DEQUEUE; /* Drop dequeue */
+	q->split_gso = TC_DUALPI2_SPLIT_GSO_SPLIT_GSO;	/* Split GSO */
+}
+
+static int dualpi2_init(struct Qdisc *sch, struct nlattr *opt,
+			struct netlink_ext_ack *extack)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+	int err;
+
+	q->l_queue = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
+				       TC_H_MAKE(sch->handle, 1), extack);
+	if (!q->l_queue)
+		return -ENOMEM;
+
+	err = tcf_block_get(&q->tcf_block, &q->tcf_filters, sch, extack);
+	if (err)
+		return err;
+
+	q->sch = sch;
+	dualpi2_reset_default(sch);
+	hrtimer_setup(&q->pi2_timer, dualpi2_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
+
+	if (opt && nla_len(opt)) {
+		err = dualpi2_change(sch, opt, extack);
+
+		if (err)
+			return err;
+	}
+
+	hrtimer_start(&q->pi2_timer, next_pi2_timeout(q),
+		      HRTIMER_MODE_ABS_PINNED);
+	return 0;
+}
+
+static int dualpi2_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+	struct nlattr *opts;
+	bool step_in_pkts;
+	u32 step_th;
+
+	step_in_pkts = READ_ONCE(q->step_in_packets);
+	step_th = READ_ONCE(q->step_thresh);
+
+	opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
+	if (!opts)
+		goto nla_put_failure;
+
+	if (step_in_pkts &&
+	    (nla_put_u32(skb, TCA_DUALPI2_LIMIT, READ_ONCE(sch->limit)) ||
+	    nla_put_u32(skb, TCA_DUALPI2_MEMORY_LIMIT,
+			READ_ONCE(q->memory_limit)) ||
+	    nla_put_u32(skb, TCA_DUALPI2_TARGET,
+			convert_ns_to_usec(READ_ONCE(q->pi2_target))) ||
+	    nla_put_u32(skb, TCA_DUALPI2_TUPDATE,
+			convert_ns_to_usec(READ_ONCE(q->pi2_tupdate))) ||
+	    nla_put_u32(skb, TCA_DUALPI2_ALPHA,
+			dualpi2_unscale_alpha_beta(READ_ONCE(q->pi2_alpha))) ||
+	    nla_put_u32(skb, TCA_DUALPI2_BETA,
+			dualpi2_unscale_alpha_beta(READ_ONCE(q->pi2_beta))) ||
+	    nla_put_u32(skb, TCA_DUALPI2_STEP_THRESH_PKTS, step_th) ||
+	    nla_put_u32(skb, TCA_DUALPI2_MIN_QLEN_STEP,
+			READ_ONCE(q->min_qlen_step)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_COUPLING,
+		       READ_ONCE(q->coupling_factor)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_DROP_OVERLOAD,
+		       READ_ONCE(q->drop_overload)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_DROP_EARLY,
+		       READ_ONCE(q->drop_early)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_C_PROTECTION,
+		       READ_ONCE(q->c_protection_wc)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_ECN_MASK, READ_ONCE(q->ecn_mask)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_SPLIT_GSO, READ_ONCE(q->split_gso))))
+		goto nla_put_failure;
+
+	if (!step_in_pkts &&
+	    (nla_put_u32(skb, TCA_DUALPI2_LIMIT, READ_ONCE(sch->limit)) ||
+	    nla_put_u32(skb, TCA_DUALPI2_MEMORY_LIMIT,
+			READ_ONCE(q->memory_limit)) ||
+	    nla_put_u32(skb, TCA_DUALPI2_TARGET,
+			convert_ns_to_usec(READ_ONCE(q->pi2_target))) ||
+	    nla_put_u32(skb, TCA_DUALPI2_TUPDATE,
+			convert_ns_to_usec(READ_ONCE(q->pi2_tupdate))) ||
+	    nla_put_u32(skb, TCA_DUALPI2_ALPHA,
+			dualpi2_unscale_alpha_beta(READ_ONCE(q->pi2_alpha))) ||
+	    nla_put_u32(skb, TCA_DUALPI2_BETA,
+			dualpi2_unscale_alpha_beta(READ_ONCE(q->pi2_beta))) ||
+	    nla_put_u32(skb, TCA_DUALPI2_STEP_THRESH_US,
+			convert_ns_to_usec(step_th)) ||
+	    nla_put_u32(skb, TCA_DUALPI2_MIN_QLEN_STEP,
+			READ_ONCE(q->min_qlen_step)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_COUPLING,
+		       READ_ONCE(q->coupling_factor)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_DROP_OVERLOAD,
+		       READ_ONCE(q->drop_overload)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_DROP_EARLY,
+		       READ_ONCE(q->drop_early)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_C_PROTECTION,
+		       READ_ONCE(q->c_protection_wc)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_ECN_MASK, READ_ONCE(q->ecn_mask)) ||
+	    nla_put_u8(skb, TCA_DUALPI2_SPLIT_GSO, READ_ONCE(q->split_gso))))
+		goto nla_put_failure;
+
+	return nla_nest_end(skb, opts);
+
+nla_put_failure:
+	nla_nest_cancel(skb, opts);
+	return -1;
+}
+
+static int dualpi2_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+	struct tc_dualpi2_xstats st = {
+		.prob			= READ_ONCE(q->pi2_prob),
+		.packets_in_c		= q->packets_in_c,
+		.packets_in_l		= q->packets_in_l,
+		.maxq			= q->maxq,
+		.ecn_mark		= q->ecn_mark,
+		.credit			= q->c_protection_credit,
+		.step_marks		= q->step_marks,
+		.memory_used		= q->memory_used,
+		.max_memory_used	= q->max_memory_used,
+		.memory_limit		= q->memory_limit,
+	};
+	u64 qc, ql;
+
+	get_queue_delays(q, &qc, &ql);
+	st.delay_l = convert_ns_to_usec(ql);
+	st.delay_c = convert_ns_to_usec(qc);
+	return gnet_stats_copy_app(d, &st, sizeof(st));
+}
+
+/* Reset both L-queue and C-queue, internal packet counters, PI probability,
+ * C-queue protection credit, and timestamps, while preserving current
+ * configuration of DUALPI2.
+ */
+static void dualpi2_reset(struct Qdisc *sch)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+
+	qdisc_reset_queue(sch);
+	qdisc_reset_queue(q->l_queue);
+	q->c_head_ts = 0;
+	q->l_head_ts = 0;
+	q->pi2_prob = 0;
+	q->packets_in_c = 0;
+	q->packets_in_l = 0;
+	q->maxq = 0;
+	q->ecn_mark = 0;
+	q->step_marks = 0;
+	q->memory_used = 0;
+	q->max_memory_used = 0;
+	dualpi2_reset_c_protection(q);
+}
+
+static void dualpi2_destroy(struct Qdisc *sch)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+
+	q->pi2_tupdate = 0;
+	hrtimer_cancel(&q->pi2_timer);
+	if (q->l_queue)
+		qdisc_put(q->l_queue);
+	tcf_block_put(q->tcf_block);
+}
+
+static struct Qdisc *dualpi2_leaf(struct Qdisc *sch, unsigned long arg)
+{
+	return NULL;
+}
+
+static unsigned long dualpi2_find(struct Qdisc *sch, u32 classid)
+{
+	return 0;
+}
+
+static unsigned long dualpi2_bind(struct Qdisc *sch, unsigned long parent,
+				  u32 classid)
+{
+	return 0;
+}
+
+static void dualpi2_unbind(struct Qdisc *q, unsigned long cl)
+{
+}
+
+static struct tcf_block *dualpi2_tcf_block(struct Qdisc *sch, unsigned long cl,
+					   struct netlink_ext_ack *extack)
+{
+	struct dualpi2_sched_data *q = qdisc_priv(sch);
+
+	if (cl)
+		return NULL;
+	return q->tcf_block;
+}
+
+static void dualpi2_walk(struct Qdisc *sch, struct qdisc_walker *arg)
+{
+	unsigned int i;
+
+	if (arg->stop)
+		return;
+
+	/* We statically define only 2 queues */
+	for (i = 0; i < 2; i++) {
+		if (arg->count < arg->skip) {
+			arg->count++;
+			continue;
+		}
+		if (arg->fn(sch, i + 1, arg) < 0) {
+			arg->stop = 1;
+			break;
+		}
+		arg->count++;
+	}
+}
+
+/* Minimal class support to handle tc filters */
+static const struct Qdisc_class_ops dualpi2_class_ops = {
+	.leaf		= dualpi2_leaf,
+	.find		= dualpi2_find,
+	.tcf_block	= dualpi2_tcf_block,
+	.bind_tcf	= dualpi2_bind,
+	.unbind_tcf	= dualpi2_unbind,
+	.walk		= dualpi2_walk,
+};
+
+static struct Qdisc_ops dualpi2_qdisc_ops __read_mostly = {
+	.id		= "dualpi2",
+	.cl_ops		= &dualpi2_class_ops,
+	.priv_size	= sizeof(struct dualpi2_sched_data),
+	.enqueue	= dualpi2_qdisc_enqueue,
+	.dequeue	= dualpi2_qdisc_dequeue,
+	.peek		= qdisc_peek_dequeued,
+	.init		= dualpi2_init,
+	.destroy	= dualpi2_destroy,
+	.reset		= dualpi2_reset,
+	.change		= dualpi2_change,
+	.dump		= dualpi2_dump,
+	.dump_stats	= dualpi2_dump_stats,
+	.owner		= THIS_MODULE,
+};
+
+static int __init dualpi2_module_init(void)
+{
+	return register_qdisc(&dualpi2_qdisc_ops);
+}
+
+static void __exit dualpi2_module_exit(void)
+{
+	unregister_qdisc(&dualpi2_qdisc_ops);
+}
+
+module_init(dualpi2_module_init);
+module_exit(dualpi2_module_exit);
+
+MODULE_DESCRIPTION("Dual Queue with Proportional Integral controller Improved with a Square (dualpi2) scheduler");
+MODULE_AUTHOR("Koen De Schepper <[e-mail]>");
+MODULE_AUTHOR("Chia-Yu Chang <[e-mail]>");
+MODULE_AUTHOR("Olga Albisser <[e-mail]>");
+MODULE_AUTHOR("Henrik Steen <[e-mail]>");
+MODULE_AUTHOR("Olivier Tilmans <[e-mail]>");
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_VERSION("1.0");

tools/testing/selftests/tc-testing/config

···
 CONFIG_NET_SCH_CHOKE=m
 CONFIG_NET_SCH_CODEL=m
 CONFIG_NET_SCH_DRR=m
+CONFIG_NET_SCH_DUALPI2=m
 CONFIG_NET_SCH_ETF=m
 CONFIG_NET_SCH_FQ=m
 CONFIG_NET_SCH_FQ_CODEL=m

tools/testing/selftests/tc-testing/tc-tests/qdiscs/dualpi2.json

···
+[
+    {
+        "id": "a4c7",
+        "name": "Create DualPI2 with default setting",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p.* step_thresh 1ms min_qlen_step 0p coupling_factor 2 drop_on_overload drop_dequeue classic_protection 10% l4s_ect split_gso",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "1ea4",
+        "name": "Create DualPI2 with memlimit",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 memlimit 20000000",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p.* memlimit 20000000B",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "2130",
+        "name": "Create DualPI2 with typical_rtt and max_rtt",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 typical_rtt 20ms max_rtt 200ms",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p.* target 20ms tupdate 20ms alpha 0.042969 beta 1.496094",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "90c1",
+        "name": "Create DualPI2 with max_rtt",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 max_rtt 300ms",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p.* target 50ms tupdate 50ms alpha 0.050781 beta 0.996094",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "7b3c",
+        "name": "Create DualPI2 with any_ect option",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 any_ect",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p .* any_ect",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "49a3",
+        "name": "Create DualPI2 with overflow option",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 overflow",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p.* overflow",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "d0a1",
+        "name": "Create DualPI2 with drop_enqueue option",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 drop_enqueue",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p .* drop_enqueue",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "f051",
+        "name": "Create DualPI2 with no_split_gso option",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 no_split_gso",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p .* no_split_gso",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "456b",
+        "name": "Create DualPI2 with packet step_thresh",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 step_thresh 3p",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p .* step_thresh 3p",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "610c",
+        "name": "Create DualPI2 with packet min_qlen_step",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 min_qlen_step 1",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p .* min_qlen_step 1p",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "b4fa",
+        "name": "Create DualPI2 with packet coupling_factor",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 coupling_factor 1",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p .* coupling_factor 1",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    },
+    {
+        "id": "37f1",
+        "name": "Create DualPI2 with packet classic_protection",
+        "category": [
+            "qdisc",
+            "dualpi2"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root dualpi2 classic_protection 0",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc dualpi2 1: root refcnt [0-9]+ limit 10000p .* classic_protection 0%",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
+    }
+]

tools/testing/selftests/tc-testing/tdc.sh

···
 # If a module is required and was not compiled
 # the test that requires it will fail anyways
 try_modprobe() {
-   modprobe -q -R "$1"
-   if [ $? -ne 0 ]; then
+   if ! modprobe -q -R "$1"; then
       echo "Module $1 not found... skipping."
    else
       modprobe "$1"
···
 try_modprobe sch_hhf
 try_modprobe sch_htb
 try_modprobe sch_teql
-./tdc.py -J`nproc`
+try_modprobe sch_dualpi2
+./tdc.py -J"$(nproc)"