sched: Add Common Applications Kept Enhanced (cake) qdisc

sch_cake targets the home router use case and is intended to squeeze the
most bandwidth and latency out of even the slowest ISP links and routers,
while presenting an API simple enough that even an ISP can configure it.

Example of use on a cable ISP uplink:

tc qdisc add dev eth0 cake bandwidth 20Mbit nat docsis ack-filter

To shape a cable download link (ifb and tc-mirred setup elided)

tc qdisc add dev ifb0 cake bandwidth 200mbit nat docsis ingress wash

CAKE is filled with:

* A hybrid Codel/Blue AQM algorithm, "Cobalt", tied to an FQ_Codel
  derived Flow Queuing system, which autoconfigures based on the bandwidth.
* A novel "triple-isolate" mode (the default) which balances per-host
  and per-flow FQ even through NAT.
* An deficit based shaper, that can also be used in an unlimited mode.
* 8 way set associative hashing to reduce flow collisions to a minimum.
* A reasonable interpretation of various diffserv latency/loss tradeoffs.
* Support for zeroing diffserv markings for entering and exiting traffic.
* Support for interacting well with Docsis 3.0 shaper framing.
* Extensive support for DSL framing types.
* Support for ack filtering.
* Extensive statistics for measuring, loss, ecn markings, latency
  variation.

A paper describing the design of CAKE is available at
https://arxiv.org/abs/1804.07617, and will be published at the 2018 IEEE
International Symposium on Local and Metropolitan Area Networks (LANMAN).

This patch adds the base shaper and packet scheduler, while subsequent
commits add the optional (configurable) features. The full userspace API
and most data structures are included in this commit, but options not
understood in the base version will be ignored.

Various versions baking have been available as an out of tree build for
kernel versions going back to 3.10, as the embedded router world has been
running a few years behind mainline Linux. A stable version has been
generally available on lede-17.01 and later.

sch_cake replaces a combination of iptables, tc filter, htb and fq_codel
in the sqm-scripts, with sane defaults and vastly simpler configuration.

CAKE's principal author is Jonathan Morton, with contributions from
Kevin Darbyshire-Bryant, Toke Høiland-Jørgensen, Sebastian Moeller,
Ryan Mounce, Tony Ambardar, Dean Scarff, Nils Andreas Svee, Dave Täht,
and Loganaden Velvindron.

Testing from Pete Heist, Georgios Amanakis, and the many other members of
the cake@lists.bufferbloat.net mailing list.

tc -s qdisc show dev eth2
 qdisc cake 8017: root refcnt 2 bandwidth 1Gbit diffserv3 triple-isolate split-gso rtt 100.0ms noatm overhead 38 mpu 84
 Sent 51504294511 bytes 37724591 pkt (dropped 6, overlimits 64958695 requeues 12)
  backlog 0b 0p requeues 12
  memory used: 1053008b of 15140Kb
  capacity estimate: 970Mbit
  min/max network layer size:           28 /    1500
  min/max overhead-adjusted size:       84 /    1538
  average network hdr offset:           14
                    Bulk  Best Effort        Voice
   thresh      62500Kbit        1Gbit      250Mbit
   target          5.0ms        5.0ms        5.0ms
   interval      100.0ms      100.0ms      100.0ms
   pk_delay          5us          5us          6us
   av_delay          3us          2us          2us
   sp_delay          2us          1us          1us
   backlog            0b           0b           0b
   pkts          3164050     25030267      9530280
   bytes      3227519915  35396974782  12879808898
   way_inds            0            8            0
   way_miss           21          366           25
   way_cols            0            0            0
   drops               5            0            1
   marks               0            0            0
   ack_drop            0            0            0
   sp_flows            1            3            0
   bk_flows            0            1            1
   un_flows            0            0            0
   max_len         68130        68130        68130

Tested-by: Pete Heist <peteheist@gmail.com>
Tested-by: Georgios Amanakis <gamanakis@gmail.com>
Signed-off-by: Dave Taht <dave.taht@gmail.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 1879 insertions, 0 deletions

diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index fcc89706745b..7af246764a35 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -295,6 +295,17 @@ config NET_SCH_FQ_CODEL
 
 	  If unsure, say N.
 
+config NET_SCH_CAKE
+	tristate "Common Applications Kept Enhanced (CAKE)"
+	help
+	  Say Y here if you want to use the Common Applications Kept Enhanced
+          (CAKE) queue management algorithm.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called sch_cake.
+
+	  If unsure, say N.
+
 config NET_SCH_FQ
 	tristate "Fair Queue"
 	help
diff --git a/net/sched/Makefile b/net/sched/Makefile
index 9a5a7077d217..673ee7d26ff2 100644
--- a/net/sched/Makefile
+++ b/net/sched/Makefile
@@ -50,6 +50,7 @@ obj-$(CONFIG_NET_SCH_CHOKE)	+= sch_choke.o
 obj-$(CONFIG_NET_SCH_QFQ)	+= sch_qfq.o
 obj-$(CONFIG_NET_SCH_CODEL)	+= sch_codel.o
 obj-$(CONFIG_NET_SCH_FQ_CODEL)	+= sch_fq_codel.o
+obj-$(CONFIG_NET_SCH_CAKE)	+= sch_cake.o
 obj-$(CONFIG_NET_SCH_FQ)	+= sch_fq.o
 obj-$(CONFIG_NET_SCH_HHF)	+= sch_hhf.o
 obj-$(CONFIG_NET_SCH_PIE)	+= sch_pie.o
diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
new file mode 100644
index 000000000000..ea0272615d63
--- /dev/null
+++ b/net/sched/sch_cake.c
@@ -0,0 +1,1867 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+
+/* COMMON Applications Kept Enhanced (CAKE) discipline
+ *
+ * Copyright (C) 2014-2018 Jonathan Morton <chromatix99@gmail.com>
+ * Copyright (C) 2015-2018 Toke Høiland-Jørgensen <toke@toke.dk>
+ * Copyright (C) 2014-2018 Dave Täht <dave.taht@gmail.com>
+ * Copyright (C) 2015-2018 Sebastian Moeller <moeller0@gmx.de>
+ * (C) 2015-2018 Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>
+ * Copyright (C) 2017-2018 Ryan Mounce <ryan@mounce.com.au>
+ *
+ * The CAKE Principles:
+ *		   (or, how to have your cake and eat it too)
+ *
+ * This is a combination of several shaping, AQM and FQ techniques into one
+ * easy-to-use package:
+ *
+ * - An overall bandwidth shaper, to move the bottleneck away from dumb CPE
+ *   equipment and bloated MACs.  This operates in deficit mode (as in sch_fq),
+ *   eliminating the need for any sort of burst parameter (eg. token bucket
+ *   depth).  Burst support is limited to that necessary to overcome scheduling
+ *   latency.
+ *
+ * - A Diffserv-aware priority queue, giving more priority to certain classes,
+ *   up to a specified fraction of bandwidth.  Above that bandwidth threshold,
+ *   the priority is reduced to avoid starving other tins.
+ *
+ * - Each priority tin has a separate Flow Queue system, to isolate traffic
+ *   flows from each other.  This prevents a burst on one flow from increasing
+ *   the delay to another.  Flows are distributed to queues using a
+ *   set-associative hash function.
+ *
+ * - Each queue is actively managed by Cobalt, which is a combination of the
+ *   Codel and Blue AQM algorithms.  This serves flows fairly, and signals
+ *   congestion early via ECN (if available) and/or packet drops, to keep
+ *   latency low.  The codel parameters are auto-tuned based on the bandwidth
+ *   setting, as is necessary at low bandwidths.
+ *
+ * The configuration parameters are kept deliberately simple for ease of use.
+ * Everything has sane defaults.  Complete generality of configuration is *not*
+ * a goal.
+ *
+ * The priority queue operates according to a weighted DRR scheme, combined with
+ * a bandwidth tracker which reuses the shaper logic to detect which side of the
+ * bandwidth sharing threshold the tin is operating.  This determines whether a
+ * priority-based weight (high) or a bandwidth-based weight (low) is used for
+ * that tin in the current pass.
+ *
+ * This qdisc was inspired by Eric Dumazet's fq_codel code, which he kindly
+ * granted us permission to leverage.
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/jiffies.h>
+#include <linux/string.h>
+#include <linux/in.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/skbuff.h>
+#include <linux/jhash.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/reciprocal_div.h>
+#include <net/netlink.h>
+#include <linux/version.h>
+#include <linux/if_vlan.h>
+#include <net/pkt_sched.h>
+#include <net/pkt_cls.h>
+#include <net/tcp.h>
+#include <net/flow_dissector.h>
+
+#define CAKE_SET_WAYS (8)
+#define CAKE_MAX_TINS (8)
+#define CAKE_QUEUES (1024)
+#define CAKE_FLOW_MASK 63
+#define CAKE_FLOW_NAT_FLAG 64
+
+/* struct cobalt_params - contains codel and blue parameters
+ * @interval:	codel initial drop rate
+ * @target:     maximum persistent sojourn time & blue update rate
+ * @mtu_time:   serialisation delay of maximum-size packet
+ * @p_inc:      increment of blue drop probability (0.32 fxp)
+ * @p_dec:      decrement of blue drop probability (0.32 fxp)
+ */
+struct cobalt_params {
+	u64	interval;
+	u64	target;
+	u64	mtu_time;
+	u32	p_inc;
+	u32	p_dec;
+};
+
+/* struct cobalt_vars - contains codel and blue variables
+ * @count:		codel dropping frequency
+ * @rec_inv_sqrt:	reciprocal value of sqrt(count) >> 1
+ * @drop_next:		time to drop next packet, or when we dropped last
+ * @blue_timer:		Blue time to next drop
+ * @p_drop:		BLUE drop probability (0.32 fxp)
+ * @dropping:		set if in dropping state
+ * @ecn_marked:		set if marked
+ */
+struct cobalt_vars {
+	u32	count;
+	u32	rec_inv_sqrt;
+	ktime_t	drop_next;
+	ktime_t	blue_timer;
+	u32     p_drop;
+	bool	dropping;
+	bool    ecn_marked;
+};
+
+enum {
+	CAKE_SET_NONE = 0,
+	CAKE_SET_SPARSE,
+	CAKE_SET_SPARSE_WAIT, /* counted in SPARSE, actually in BULK */
+	CAKE_SET_BULK,
+	CAKE_SET_DECAYING
+};
+
+struct cake_flow {
+	/* this stuff is all needed per-flow at dequeue time */
+	struct sk_buff	  *head;
+	struct sk_buff	  *tail;
+	struct list_head  flowchain;
+	s32		  deficit;
+	u32		  dropped;
+	struct cobalt_vars cvars;
+	u16		  srchost; /* index into cake_host table */
+	u16		  dsthost;
+	u8		  set;
+}; /* please try to keep this structure <= 64 bytes */
+
+struct cake_host {
+	u32 srchost_tag;
+	u32 dsthost_tag;
+	u16 srchost_refcnt;
+	u16 dsthost_refcnt;
+};
+
+struct cake_heap_entry {
+	u16 t:3, b:10;
+};
+
+struct cake_tin_data {
+	struct cake_flow flows[CAKE_QUEUES];
+	u32	backlogs[CAKE_QUEUES];
+	u32	tags[CAKE_QUEUES]; /* for set association */
+	u16	overflow_idx[CAKE_QUEUES];
+	struct cake_host hosts[CAKE_QUEUES]; /* for triple isolation */
+	u16	flow_quantum;
+
+	struct cobalt_params cparams;
+	u32	drop_overlimit;
+	u16	bulk_flow_count;
+	u16	sparse_flow_count;
+	u16	decaying_flow_count;
+	u16	unresponsive_flow_count;
+
+	u32	max_skblen;
+
+	struct list_head new_flows;
+	struct list_head old_flows;
+	struct list_head decaying_flows;
+
+	/* time_next = time_this + ((len * rate_ns) >> rate_shft) */
+	ktime_t	time_next_packet;
+	u64	tin_rate_ns;
+	u64	tin_rate_bps;
+	u16	tin_rate_shft;
+
+	u16	tin_quantum_prio;
+	u16	tin_quantum_band;
+	s32	tin_deficit;
+	u32	tin_backlog;
+	u32	tin_dropped;
+	u32	tin_ecn_mark;
+
+	u32	packets;
+	u64	bytes;
+
+	u32	ack_drops;
+
+	/* moving averages */
+	u64 avge_delay;
+	u64 peak_delay;
+	u64 base_delay;
+
+	/* hash function stats */
+	u32	way_directs;
+	u32	way_hits;
+	u32	way_misses;
+	u32	way_collisions;
+}; /* number of tins is small, so size of this struct doesn't matter much */
+
+struct cake_sched_data {
+	struct tcf_proto __rcu *filter_list; /* optional external classifier */
+	struct tcf_block *block;
+	struct cake_tin_data *tins;
+
+	struct cake_heap_entry overflow_heap[CAKE_QUEUES * CAKE_MAX_TINS];
+	u16		overflow_timeout;
+
+	u16		tin_cnt;
+	u8		tin_mode;
+	u8		flow_mode;
+	u8		ack_filter;
+	u8		atm_mode;
+
+	/* time_next = time_this + ((len * rate_ns) >> rate_shft) */
+	u16		rate_shft;
+	ktime_t		time_next_packet;
+	ktime_t		failsafe_next_packet;
+	u64		rate_ns;
+	u64		rate_bps;
+	u16		rate_flags;
+	s16		rate_overhead;
+	u16		rate_mpu;
+	u64		interval;
+	u64		target;
+
+	/* resource tracking */
+	u32		buffer_used;
+	u32		buffer_max_used;
+	u32		buffer_limit;
+	u32		buffer_config_limit;
+
+	/* indices for dequeue */
+	u16		cur_tin;
+	u16		cur_flow;
+
+	struct qdisc_watchdog watchdog;
+	const u8	*tin_index;
+	const u8	*tin_order;
+
+	/* bandwidth capacity estimate */
+	ktime_t		last_packet_time;
+	ktime_t		avg_window_begin;
+	u64		avg_packet_interval;
+	u64		avg_window_bytes;
+	u64		avg_peak_bandwidth;
+	ktime_t		last_reconfig_time;
+
+	/* packet length stats */
+	u32		avg_netoff;
+	u16		max_netlen;
+	u16		max_adjlen;
+	u16		min_netlen;
+	u16		min_adjlen;
+};
+
+enum {
+	CAKE_FLAG_OVERHEAD	   = BIT(0),
+	CAKE_FLAG_AUTORATE_INGRESS = BIT(1),
+	CAKE_FLAG_INGRESS	   = BIT(2),
+	CAKE_FLAG_WASH		   = BIT(3),
+	CAKE_FLAG_SPLIT_GSO	   = BIT(4)
+};
+
+/* COBALT operates the Codel and BLUE algorithms in parallel, in order to
+ * obtain the best features of each.  Codel is excellent on flows which
+ * respond to congestion signals in a TCP-like way.  BLUE is more effective on
+ * unresponsive flows.
+ */
+
+struct cobalt_skb_cb {
+	ktime_t enqueue_time;
+};
+
+static u64 us_to_ns(u64 us)
+{
+	return us * NSEC_PER_USEC;
+}
+
+static struct cobalt_skb_cb *get_cobalt_cb(const struct sk_buff *skb)
+{
+	qdisc_cb_private_validate(skb, sizeof(struct cobalt_skb_cb));
+	return (struct cobalt_skb_cb *)qdisc_skb_cb(skb)->data;
+}
+
+static ktime_t cobalt_get_enqueue_time(const struct sk_buff *skb)
+{
+	return get_cobalt_cb(skb)->enqueue_time;
+}
+
+static void cobalt_set_enqueue_time(struct sk_buff *skb,
+				    ktime_t now)
+{
+	get_cobalt_cb(skb)->enqueue_time = now;
+}
+
+static u16 quantum_div[CAKE_QUEUES + 1] = {0};
+
+#define REC_INV_SQRT_CACHE (16)
+static u32 cobalt_rec_inv_sqrt_cache[REC_INV_SQRT_CACHE] = {0};
+
+/* http://en.wikipedia.org/wiki/Methods_of_computing_square_roots
+ * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
+ *
+ * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
+ */
+
+static void cobalt_newton_step(struct cobalt_vars *vars)
+{
+	u32 invsqrt, invsqrt2;
+	u64 val;
+
+	invsqrt = vars->rec_inv_sqrt;
+	invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
+	val = (3LL << 32) - ((u64)vars->count * invsqrt2);
+
+	val >>= 2; /* avoid overflow in following multiply */
+	val = (val * invsqrt) >> (32 - 2 + 1);
+
+	vars->rec_inv_sqrt = val;
+}
+
+static void cobalt_invsqrt(struct cobalt_vars *vars)
+{
+	if (vars->count < REC_INV_SQRT_CACHE)
+		vars->rec_inv_sqrt = cobalt_rec_inv_sqrt_cache[vars->count];
+	else
+		cobalt_newton_step(vars);
+}
+
+/* There is a big difference in timing between the accurate values placed in
+ * the cache and the approximations given by a single Newton step for small
+ * count values, particularly when stepping from count 1 to 2 or vice versa.
+ * Above 16, a single Newton step gives sufficient accuracy in either
+ * direction, given the precision stored.
+ *
+ * The magnitude of the error when stepping up to count 2 is such as to give
+ * the value that *should* have been produced at count 4.
+ */
+
+static void cobalt_cache_init(void)
+{
+	struct cobalt_vars v;
+
+	memset(&v, 0, sizeof(v));
+	v.rec_inv_sqrt = ~0U;
+	cobalt_rec_inv_sqrt_cache[0] = v.rec_inv_sqrt;
+
+	for (v.count = 1; v.count < REC_INV_SQRT_CACHE; v.count++) {
+		cobalt_newton_step(&v);
+		cobalt_newton_step(&v);
+		cobalt_newton_step(&v);
+		cobalt_newton_step(&v);
+
+		cobalt_rec_inv_sqrt_cache[v.count] = v.rec_inv_sqrt;
+	}
+}
+
+static void cobalt_vars_init(struct cobalt_vars *vars)
+{
+	memset(vars, 0, sizeof(*vars));
+
+	if (!cobalt_rec_inv_sqrt_cache[0]) {
+		cobalt_cache_init();
+		cobalt_rec_inv_sqrt_cache[0] = ~0;
+	}
+}
+
+/* CoDel control_law is t + interval/sqrt(count)
+ * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
+ * both sqrt() and divide operation.
+ */
+static ktime_t cobalt_control(ktime_t t,
+			      u64 interval,
+			      u32 rec_inv_sqrt)
+{
+	return ktime_add_ns(t, reciprocal_scale(interval,
+						rec_inv_sqrt));
+}
+
+/* Call this when a packet had to be dropped due to queue overflow.  Returns
+ * true if the BLUE state was quiescent before but active after this call.
+ */
+static bool cobalt_queue_full(struct cobalt_vars *vars,
+			      struct cobalt_params *p,
+			      ktime_t now)
+{
+	bool up = false;
+
+	if (ktime_to_ns(ktime_sub(now, vars->blue_timer)) > p->target) {
+		up = !vars->p_drop;
+		vars->p_drop += p->p_inc;
+		if (vars->p_drop < p->p_inc)
+			vars->p_drop = ~0;
+		vars->blue_timer = now;
+	}
+	vars->dropping = true;
+	vars->drop_next = now;
+	if (!vars->count)
+		vars->count = 1;
+
+	return up;
+}
+
+/* Call this when the queue was serviced but turned out to be empty.  Returns
+ * true if the BLUE state was active before but quiescent after this call.
+ */
+static bool cobalt_queue_empty(struct cobalt_vars *vars,
+			       struct cobalt_params *p,
+			       ktime_t now)
+{
+	bool down = false;
+
+	if (vars->p_drop &&
+	    ktime_to_ns(ktime_sub(now, vars->blue_timer)) > p->target) {
+		if (vars->p_drop < p->p_dec)
+			vars->p_drop = 0;
+		else
+			vars->p_drop -= p->p_dec;
+		vars->blue_timer = now;
+		down = !vars->p_drop;
+	}
+	vars->dropping = false;
+
+	if (vars->count && ktime_to_ns(ktime_sub(now, vars->drop_next)) >= 0) {
+		vars->count--;
+		cobalt_invsqrt(vars);
+		vars->drop_next = cobalt_control(vars->drop_next,
+						 p->interval,
+						 vars->rec_inv_sqrt);
+	}
+
+	return down;
+}
+
+/* Call this with a freshly dequeued packet for possible congestion marking.
+ * Returns true as an instruction to drop the packet, false for delivery.
+ */
+static bool cobalt_should_drop(struct cobalt_vars *vars,
+			       struct cobalt_params *p,
+			       ktime_t now,
+			       struct sk_buff *skb)
+{
+	bool next_due, over_target, drop = false;
+	ktime_t schedule;
+	u64 sojourn;
+
+/* The 'schedule' variable records, in its sign, whether 'now' is before or
+ * after 'drop_next'.  This allows 'drop_next' to be updated before the next
+ * scheduling decision is actually branched, without destroying that
+ * information.  Similarly, the first 'schedule' value calculated is preserved
+ * in the boolean 'next_due'.
+ *
+ * As for 'drop_next', we take advantage of the fact that 'interval' is both
+ * the delay between first exceeding 'target' and the first signalling event,
+ * *and* the scaling factor for the signalling frequency.  It's therefore very
+ * natural to use a single mechanism for both purposes, and eliminates a
+ * significant amount of reference Codel's spaghetti code.  To help with this,
+ * both the '0' and '1' entries in the invsqrt cache are 0xFFFFFFFF, as close
+ * as possible to 1.0 in fixed-point.
+ */
+
+	sojourn = ktime_to_ns(ktime_sub(now, cobalt_get_enqueue_time(skb)));
+	schedule = ktime_sub(now, vars->drop_next);
+	over_target = sojourn > p->target &&
+		      sojourn > p->mtu_time * 4;
+	next_due = vars->count && ktime_to_ns(schedule) >= 0;
+
+	vars->ecn_marked = false;
+
+	if (over_target) {
+		if (!vars->dropping) {
+			vars->dropping = true;
+			vars->drop_next = cobalt_control(now,
+							 p->interval,
+							 vars->rec_inv_sqrt);
+		}
+		if (!vars->count)
+			vars->count = 1;
+	} else if (vars->dropping) {
+		vars->dropping = false;
+	}
+
+	if (next_due && vars->dropping) {
+		/* Use ECN mark if possible, otherwise drop */
+		drop = !(vars->ecn_marked = INET_ECN_set_ce(skb));
+
+		vars->count++;
+		if (!vars->count)
+			vars->count--;
+		cobalt_invsqrt(vars);
+		vars->drop_next = cobalt_control(vars->drop_next,
+						 p->interval,
+						 vars->rec_inv_sqrt);
+		schedule = ktime_sub(now, vars->drop_next);
+	} else {
+		while (next_due) {
+			vars->count--;
+			cobalt_invsqrt(vars);
+			vars->drop_next = cobalt_control(vars->drop_next,
+							 p->interval,
+							 vars->rec_inv_sqrt);
+			schedule = ktime_sub(now, vars->drop_next);
+			next_due = vars->count && ktime_to_ns(schedule) >= 0;
+		}
+	}
+
+	/* Simple BLUE implementation.  Lack of ECN is deliberate. */
+	if (vars->p_drop)
+		drop |= (prandom_u32() < vars->p_drop);
+
+	/* Overload the drop_next field as an activity timeout */
+	if (!vars->count)
+		vars->drop_next = ktime_add_ns(now, p->interval);
+	else if (ktime_to_ns(schedule) > 0 && !drop)
+		vars->drop_next = now;
+
+	return drop;
+}
+
+/* Cake has several subtle multiple bit settings. In these cases you
+ *  would be matching triple isolate mode as well.
+ */
+
+static bool cake_dsrc(int flow_mode)
+{
+	return (flow_mode & CAKE_FLOW_DUAL_SRC) == CAKE_FLOW_DUAL_SRC;
+}
+
+static bool cake_ddst(int flow_mode)
+{
+	return (flow_mode & CAKE_FLOW_DUAL_DST) == CAKE_FLOW_DUAL_DST;
+}
+
+static u32 cake_hash(struct cake_tin_data *q, const struct sk_buff *skb,
+		     int flow_mode)
+{
+	u32 flow_hash = 0, srchost_hash, dsthost_hash;
+	u16 reduced_hash, srchost_idx, dsthost_idx;
+	struct flow_keys keys, host_keys;
+
+	if (unlikely(flow_mode == CAKE_FLOW_NONE))
+		return 0;
+
+	skb_flow_dissect_flow_keys(skb, &keys,
+				   FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
+
+	/* flow_hash_from_keys() sorts the addresses by value, so we have
+	 * to preserve their order in a separate data structure to treat
+	 * src and dst host addresses as independently selectable.
+	 */
+	host_keys = keys;
+	host_keys.ports.ports     = 0;
+	host_keys.basic.ip_proto  = 0;
+	host_keys.keyid.keyid     = 0;
+	host_keys.tags.flow_label = 0;
+
+	switch (host_keys.control.addr_type) {
+	case FLOW_DISSECTOR_KEY_IPV4_ADDRS:
+		host_keys.addrs.v4addrs.src = 0;
+		dsthost_hash = flow_hash_from_keys(&host_keys);
+		host_keys.addrs.v4addrs.src = keys.addrs.v4addrs.src;
+		host_keys.addrs.v4addrs.dst = 0;
+		srchost_hash = flow_hash_from_keys(&host_keys);
+		break;
+
+	case FLOW_DISSECTOR_KEY_IPV6_ADDRS:
+		memset(&host_keys.addrs.v6addrs.src, 0,
+		       sizeof(host_keys.addrs.v6addrs.src));
+		dsthost_hash = flow_hash_from_keys(&host_keys);
+		host_keys.addrs.v6addrs.src = keys.addrs.v6addrs.src;
+		memset(&host_keys.addrs.v6addrs.dst, 0,
+		       sizeof(host_keys.addrs.v6addrs.dst));
+		srchost_hash = flow_hash_from_keys(&host_keys);
+		break;
+
+	default:
+		dsthost_hash = 0;
+		srchost_hash = 0;
+	}
+
+	/* This *must* be after the above switch, since as a
+	 * side-effect it sorts the src and dst addresses.
+	 */
+	if (flow_mode & CAKE_FLOW_FLOWS)
+		flow_hash = flow_hash_from_keys(&keys);
+
+	if (!(flow_mode & CAKE_FLOW_FLOWS)) {
+		if (flow_mode & CAKE_FLOW_SRC_IP)
+			flow_hash ^= srchost_hash;
+
+		if (flow_mode & CAKE_FLOW_DST_IP)
+			flow_hash ^= dsthost_hash;
+	}
+
+	reduced_hash = flow_hash % CAKE_QUEUES;
+
+	/* set-associative hashing */
+	/* fast path if no hash collision (direct lookup succeeds) */
+	if (likely(q->tags[reduced_hash] == flow_hash &&
+		   q->flows[reduced_hash].set)) {
+		q->way_directs++;
+	} else {
+		u32 inner_hash = reduced_hash % CAKE_SET_WAYS;
+		u32 outer_hash = reduced_hash - inner_hash;
+		bool allocate_src = false;
+		bool allocate_dst = false;
+		u32 i, k;
+
+		/* check if any active queue in the set is reserved for
+		 * this flow.
+		 */
+		for (i = 0, k = inner_hash; i < CAKE_SET_WAYS;
+		     i++, k = (k + 1) % CAKE_SET_WAYS) {
+			if (q->tags[outer_hash + k] == flow_hash) {
+				if (i)
+					q->way_hits++;
+
+				if (!q->flows[outer_hash + k].set) {
+					/* need to increment host refcnts */
+					allocate_src = cake_dsrc(flow_mode);
+					allocate_dst = cake_ddst(flow_mode);
+				}
+
+				goto found;
+			}
+		}
+
+		/* no queue is reserved for this flow, look for an
+		 * empty one.
+		 */
+		for (i = 0; i < CAKE_SET_WAYS;
+			 i++, k = (k + 1) % CAKE_SET_WAYS) {
+			if (!q->flows[outer_hash + k].set) {
+				q->way_misses++;
+				allocate_src = cake_dsrc(flow_mode);
+				allocate_dst = cake_ddst(flow_mode);
+				goto found;
+			}
+		}
+
+		/* With no empty queues, default to the original
+		 * queue, accept the collision, update the host tags.
+		 */
+		q->way_collisions++;
+		q->hosts[q->flows[reduced_hash].srchost].srchost_refcnt--;
+		q->hosts[q->flows[reduced_hash].dsthost].dsthost_refcnt--;
+		allocate_src = cake_dsrc(flow_mode);
+		allocate_dst = cake_ddst(flow_mode);
+found:
+		/* reserve queue for future packets in same flow */
+		reduced_hash = outer_hash + k;
+		q->tags[reduced_hash] = flow_hash;
+
+		if (allocate_src) {
+			srchost_idx = srchost_hash % CAKE_QUEUES;
+			inner_hash = srchost_idx % CAKE_SET_WAYS;
+			outer_hash = srchost_idx - inner_hash;
+			for (i = 0, k = inner_hash; i < CAKE_SET_WAYS;
+				i++, k = (k + 1) % CAKE_SET_WAYS) {
+				if (q->hosts[outer_hash + k].srchost_tag ==
+				    srchost_hash)
+					goto found_src;
+			}
+			for (i = 0; i < CAKE_SET_WAYS;
+				i++, k = (k + 1) % CAKE_SET_WAYS) {
+				if (!q->hosts[outer_hash + k].srchost_refcnt)
+					break;
+			}
+			q->hosts[outer_hash + k].srchost_tag = srchost_hash;
+found_src:
+			srchost_idx = outer_hash + k;
+			q->hosts[srchost_idx].srchost_refcnt++;
+			q->flows[reduced_hash].srchost = srchost_idx;
+		}
+
+		if (allocate_dst) {
+			dsthost_idx = dsthost_hash % CAKE_QUEUES;
+			inner_hash = dsthost_idx % CAKE_SET_WAYS;
+			outer_hash = dsthost_idx - inner_hash;
+			for (i = 0, k = inner_hash; i < CAKE_SET_WAYS;
+			     i++, k = (k + 1) % CAKE_SET_WAYS) {
+				if (q->hosts[outer_hash + k].dsthost_tag ==
+				    dsthost_hash)
+					goto found_dst;
+			}
+			for (i = 0; i < CAKE_SET_WAYS;
+			     i++, k = (k + 1) % CAKE_SET_WAYS) {
+				if (!q->hosts[outer_hash + k].dsthost_refcnt)
+					break;
+			}
+			q->hosts[outer_hash + k].dsthost_tag = dsthost_hash;
+found_dst:
+			dsthost_idx = outer_hash + k;
+			q->hosts[dsthost_idx].dsthost_refcnt++;
+			q->flows[reduced_hash].dsthost = dsthost_idx;
+		}
+	}
+
+	return reduced_hash;
+}
+
+/* helper functions : might be changed when/if skb use a standard list_head */
+/* remove one skb from head of slot queue */
+
+static struct sk_buff *dequeue_head(struct cake_flow *flow)
+{
+	struct sk_buff *skb = flow->head;
+
+	if (skb) {
+		flow->head = skb->next;
+		skb->next = NULL;
+	}
+
+	return skb;
+}
+
+/* add skb to flow queue (tail add) */
+
+static void flow_queue_add(struct cake_flow *flow, struct sk_buff *skb)
+{
+	if (!flow->head)
+		flow->head = skb;
+	else
+		flow->tail->next = skb;
+	flow->tail = skb;
+	skb->next = NULL;
+}
+
+static u64 cake_ewma(u64 avg, u64 sample, u32 shift)
+{
+	avg -= avg >> shift;
+	avg += sample >> shift;
+	return avg;
+}
+
+static void cake_heap_swap(struct cake_sched_data *q, u16 i, u16 j)
+{
+	struct cake_heap_entry ii = q->overflow_heap[i];
+	struct cake_heap_entry jj = q->overflow_heap[j];
+
+	q->overflow_heap[i] = jj;
+	q->overflow_heap[j] = ii;
+
+	q->tins[ii.t].overflow_idx[ii.b] = j;
+	q->tins[jj.t].overflow_idx[jj.b] = i;
+}
+
+static u32 cake_heap_get_backlog(const struct cake_sched_data *q, u16 i)
+{
+	struct cake_heap_entry ii = q->overflow_heap[i];
+
+	return q->tins[ii.t].backlogs[ii.b];
+}
+
+static void cake_heapify(struct cake_sched_data *q, u16 i)
+{
+	static const u32 a = CAKE_MAX_TINS * CAKE_QUEUES;
+	u32 mb = cake_heap_get_backlog(q, i);
+	u32 m = i;
+
+	while (m < a) {
+		u32 l = m + m + 1;
+		u32 r = l + 1;
+
+		if (l < a) {
+			u32 lb = cake_heap_get_backlog(q, l);
+
+			if (lb > mb) {
+				m  = l;
+				mb = lb;
+			}
+		}
+
+		if (r < a) {
+			u32 rb = cake_heap_get_backlog(q, r);
+
+			if (rb > mb) {
+				m  = r;
+				mb = rb;
+			}
+		}
+
+		if (m != i) {
+			cake_heap_swap(q, i, m);
+			i = m;
+		} else {
+			break;
+		}
+	}
+}
+
+static void cake_heapify_up(struct cake_sched_data *q, u16 i)
+{
+	while (i > 0 && i < CAKE_MAX_TINS * CAKE_QUEUES) {
+		u16 p = (i - 1) >> 1;
+		u32 ib = cake_heap_get_backlog(q, i);
+		u32 pb = cake_heap_get_backlog(q, p);
+
+		if (ib > pb) {
+			cake_heap_swap(q, i, p);
+			i = p;
+		} else {
+			break;
+		}
+	}
+}
+
+static int cake_advance_shaper(struct cake_sched_data *q,
+			       struct cake_tin_data *b,
+			       struct sk_buff *skb,
+			       ktime_t now, bool drop)
+{
+	u32 len = qdisc_pkt_len(skb);
+
+	/* charge packet bandwidth to this tin
+	 * and to the global shaper.
+	 */
+	if (q->rate_ns) {
+		u64 tin_dur = (len * b->tin_rate_ns) >> b->tin_rate_shft;
+		u64 global_dur = (len * q->rate_ns) >> q->rate_shft;
+		u64 failsafe_dur = global_dur + (global_dur >> 1);
+
+		if (ktime_before(b->time_next_packet, now))
+			b->time_next_packet = ktime_add_ns(b->time_next_packet,
+							   tin_dur);
+
+		else if (ktime_before(b->time_next_packet,
+				      ktime_add_ns(now, tin_dur)))
+			b->time_next_packet = ktime_add_ns(now, tin_dur);
+
+		q->time_next_packet = ktime_add_ns(q->time_next_packet,
+						   global_dur);
+		if (!drop)
+			q->failsafe_next_packet = \
+				ktime_add_ns(q->failsafe_next_packet,
+					     failsafe_dur);
+	}
+	return len;
+}
+
+static unsigned int cake_drop(struct Qdisc *sch, struct sk_buff **to_free)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	ktime_t now = ktime_get();
+	u32 idx = 0, tin = 0, len;
+	struct cake_heap_entry qq;
+	struct cake_tin_data *b;
+	struct cake_flow *flow;
+	struct sk_buff *skb;
+
+	if (!q->overflow_timeout) {
+		int i;
+		/* Build fresh max-heap */
+		for (i = CAKE_MAX_TINS * CAKE_QUEUES / 2; i >= 0; i--)
+			cake_heapify(q, i);
+	}
+	q->overflow_timeout = 65535;
+
+	/* select longest queue for pruning */
+	qq  = q->overflow_heap[0];
+	tin = qq.t;
+	idx = qq.b;
+
+	b = &q->tins[tin];
+	flow = &b->flows[idx];
+	skb = dequeue_head(flow);
+	if (unlikely(!skb)) {
+		/* heap has gone wrong, rebuild it next time */
+		q->overflow_timeout = 0;
+		return idx + (tin << 16);
+	}
+
+	if (cobalt_queue_full(&flow->cvars, &b->cparams, now))
+		b->unresponsive_flow_count++;
+
+	len = qdisc_pkt_len(skb);
+	q->buffer_used      -= skb->truesize;
+	b->backlogs[idx]    -= len;
+	b->tin_backlog      -= len;
+	sch->qstats.backlog -= len;
+	qdisc_tree_reduce_backlog(sch, 1, len);
+
+	flow->dropped++;
+	b->tin_dropped++;
+	sch->qstats.drops++;
+
+	__qdisc_drop(skb, to_free);
+	sch->q.qlen--;
+
+	cake_heapify(q, 0);
+
+	return idx + (tin << 16);
+}
+
+static u32 cake_classify(struct Qdisc *sch, struct cake_tin_data *t,
+			 struct sk_buff *skb, int flow_mode, int *qerr)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	struct tcf_proto *filter;
+	struct tcf_result res;
+	int result;
+
+	filter = rcu_dereference_bh(q->filter_list);
+	if (!filter)
+		return cake_hash(t, skb, flow_mode) + 1;
+
+	*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
+	result = tcf_classify(skb, filter, &res, false);
+	if (result >= 0) {
+#ifdef CONFIG_NET_CLS_ACT
+		switch (result) {
+		case TC_ACT_STOLEN:
+		case TC_ACT_QUEUED:
+		case TC_ACT_TRAP:
+			*qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
+			/* fall through */
+		case TC_ACT_SHOT:
+			return 0;
+		}
+#endif
+		if (TC_H_MIN(res.classid) <= CAKE_QUEUES)
+			return TC_H_MIN(res.classid);
+	}
+	return 0;
+}
+
+static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
+			struct sk_buff **to_free)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	int len = qdisc_pkt_len(skb);
+	int uninitialized_var(ret);
+	ktime_t now = ktime_get();
+	struct cake_tin_data *b;
+	struct cake_flow *flow;
+	u32 idx, tin;
+
+	tin = 0;
+	b = &q->tins[tin];
+
+	/* choose flow to insert into */
+	idx = cake_classify(sch, b, skb, q->flow_mode, &ret);
+	if (idx == 0) {
+		if (ret & __NET_XMIT_BYPASS)
+			qdisc_qstats_drop(sch);
+		__qdisc_drop(skb, to_free);
+		return ret;
+	}
+	idx--;
+	flow = &b->flows[idx];
+
+	/* ensure shaper state isn't stale */
+	if (!b->tin_backlog) {
+		if (ktime_before(b->time_next_packet, now))
+			b->time_next_packet = now;
+
+		if (!sch->q.qlen) {
+			if (ktime_before(q->time_next_packet, now)) {
+				q->failsafe_next_packet = now;
+				q->time_next_packet = now;
+			} else if (ktime_after(q->time_next_packet, now) &&
+				   ktime_after(q->failsafe_next_packet, now)) {
+				u64 next = \
+					min(ktime_to_ns(q->time_next_packet),
+					    ktime_to_ns(
+						   q->failsafe_next_packet));
+				sch->qstats.overlimits++;
+				qdisc_watchdog_schedule_ns(&q->watchdog, next);
+			}
+		}
+	}
+
+	if (unlikely(len > b->max_skblen))
+		b->max_skblen = len;
+
+	cobalt_set_enqueue_time(skb, now);
+	flow_queue_add(flow, skb);
+
+	sch->q.qlen++;
+	q->buffer_used      += skb->truesize;
+
+	/* stats */
+	b->packets++;
+	b->bytes	    += len;
+	b->backlogs[idx]    += len;
+	b->tin_backlog      += len;
+	sch->qstats.backlog += len;
+	q->avg_window_bytes += len;
+
+	if (q->overflow_timeout)
+		cake_heapify_up(q, b->overflow_idx[idx]);
+
+	/* incoming bandwidth capacity estimate */
+	q->avg_window_bytes = 0;
+	q->last_packet_time = now;
+
+	/* flowchain */
+	if (!flow->set || flow->set == CAKE_SET_DECAYING) {
+		struct cake_host *srchost = &b->hosts[flow->srchost];
+		struct cake_host *dsthost = &b->hosts[flow->dsthost];
+		u16 host_load = 1;
+
+		if (!flow->set) {
+			list_add_tail(&flow->flowchain, &b->new_flows);
+		} else {
+			b->decaying_flow_count--;
+			list_move_tail(&flow->flowchain, &b->new_flows);
+		}
+		flow->set = CAKE_SET_SPARSE;
+		b->sparse_flow_count++;
+
+		if (cake_dsrc(q->flow_mode))
+			host_load = max(host_load, srchost->srchost_refcnt);
+
+		if (cake_ddst(q->flow_mode))
+			host_load = max(host_load, dsthost->dsthost_refcnt);
+
+		flow->deficit = (b->flow_quantum *
+				 quantum_div[host_load]) >> 16;
+	} else if (flow->set == CAKE_SET_SPARSE_WAIT) {
+		/* this flow was empty, accounted as a sparse flow, but actually
+		 * in the bulk rotation.
+		 */
+		flow->set = CAKE_SET_BULK;
+		b->sparse_flow_count--;
+		b->bulk_flow_count++;
+	}
+
+	if (q->buffer_used > q->buffer_max_used)
+		q->buffer_max_used = q->buffer_used;
+
+	if (q->buffer_used > q->buffer_limit) {
+		u32 dropped = 0;
+
+		while (q->buffer_used > q->buffer_limit) {
+			dropped++;
+			cake_drop(sch, to_free);
+		}
+		b->drop_overlimit += dropped;
+	}
+	return NET_XMIT_SUCCESS;
+}
+
+static struct sk_buff *cake_dequeue_one(struct Qdisc *sch)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	struct cake_tin_data *b = &q->tins[q->cur_tin];
+	struct cake_flow *flow = &b->flows[q->cur_flow];
+	struct sk_buff *skb = NULL;
+	u32 len;
+
+	if (flow->head) {
+		skb = dequeue_head(flow);
+		len = qdisc_pkt_len(skb);
+		b->backlogs[q->cur_flow] -= len;
+		b->tin_backlog		 -= len;
+		sch->qstats.backlog      -= len;
+		q->buffer_used		 -= skb->truesize;
+		sch->q.qlen--;
+
+		if (q->overflow_timeout)
+			cake_heapify(q, b->overflow_idx[q->cur_flow]);
+	}
+	return skb;
+}
+
+/* Discard leftover packets from a tin no longer in use. */
+static void cake_clear_tin(struct Qdisc *sch, u16 tin)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	struct sk_buff *skb;
+
+	q->cur_tin = tin;
+	for (q->cur_flow = 0; q->cur_flow < CAKE_QUEUES; q->cur_flow++)
+		while (!!(skb = cake_dequeue_one(sch)))
+			kfree_skb(skb);
+}
+
+static struct sk_buff *cake_dequeue(struct Qdisc *sch)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	struct cake_tin_data *b = &q->tins[q->cur_tin];
+	struct cake_host *srchost, *dsthost;
+	ktime_t now = ktime_get();
+	struct cake_flow *flow;
+	struct list_head *head;
+	bool first_flow = true;
+	struct sk_buff *skb;
+	u16 host_load;
+	u64 delay;
+	u32 len;
+
+begin:
+	if (!sch->q.qlen)
+		return NULL;
+
+	/* global hard shaper */
+	if (ktime_after(q->time_next_packet, now) &&
+	    ktime_after(q->failsafe_next_packet, now)) {
+		u64 next = min(ktime_to_ns(q->time_next_packet),
+			       ktime_to_ns(q->failsafe_next_packet));
+
+		sch->qstats.overlimits++;
+		qdisc_watchdog_schedule_ns(&q->watchdog, next);
+		return NULL;
+	}
+
+	/* Choose a class to work on. */
+	if (!q->rate_ns) {
+		/* In unlimited mode, can't rely on shaper timings, just balance
+		 * with DRR
+		 */
+		bool wrapped = false, empty = true;
+
+		while (b->tin_deficit < 0 ||
+		       !(b->sparse_flow_count + b->bulk_flow_count)) {
+			if (b->tin_deficit <= 0)
+				b->tin_deficit += b->tin_quantum_band;
+			if (b->sparse_flow_count + b->bulk_flow_count)
+				empty = false;
+
+			q->cur_tin++;
+			b++;
+			if (q->cur_tin >= q->tin_cnt) {
+				q->cur_tin = 0;
+				b = q->tins;
+
+				if (wrapped) {
+					/* It's possible for q->qlen to be
+					 * nonzero when we actually have no
+					 * packets anywhere.
+					 */
+					if (empty)
+						return NULL;
+				} else {
+					wrapped = true;
+				}
+			}
+		}
+	} else {
+		/* In shaped mode, choose:
+		 * - Highest-priority tin with queue and meeting schedule, or
+		 * - The earliest-scheduled tin with queue.
+		 */
+		ktime_t best_time = KTIME_MAX;
+		int tin, best_tin = 0;
+
+		for (tin = 0; tin < q->tin_cnt; tin++) {
+			b = q->tins + tin;
+			if ((b->sparse_flow_count + b->bulk_flow_count) > 0) {
+				ktime_t time_to_pkt = \
+					ktime_sub(b->time_next_packet, now);
+
+				if (ktime_to_ns(time_to_pkt) <= 0 ||
+				    ktime_compare(time_to_pkt,
+						  best_time) <= 0) {
+					best_time = time_to_pkt;
+					best_tin = tin;
+				}
+			}
+		}
+
+		q->cur_tin = best_tin;
+		b = q->tins + best_tin;
+
+		/* No point in going further if no packets to deliver. */
+		if (unlikely(!(b->sparse_flow_count + b->bulk_flow_count)))
+			return NULL;
+	}
+
+retry:
+	/* service this class */
+	head = &b->decaying_flows;
+	if (!first_flow || list_empty(head)) {
+		head = &b->new_flows;
+		if (list_empty(head)) {
+			head = &b->old_flows;
+			if (unlikely(list_empty(head))) {
+				head = &b->decaying_flows;
+				if (unlikely(list_empty(head)))
+					goto begin;
+			}
+		}
+	}
+	flow = list_first_entry(head, struct cake_flow, flowchain);
+	q->cur_flow = flow - b->flows;
+	first_flow = false;
+
+	/* triple isolation (modified DRR++) */
+	srchost = &b->hosts[flow->srchost];
+	dsthost = &b->hosts[flow->dsthost];
+	host_load = 1;
+
+	if (cake_dsrc(q->flow_mode))
+		host_load = max(host_load, srchost->srchost_refcnt);
+
+	if (cake_ddst(q->flow_mode))
+		host_load = max(host_load, dsthost->dsthost_refcnt);
+
+	WARN_ON(host_load > CAKE_QUEUES);
+
+	/* flow isolation (DRR++) */
+	if (flow->deficit <= 0) {
+		/* The shifted prandom_u32() is a way to apply dithering to
+		 * avoid accumulating roundoff errors
+		 */
+		flow->deficit += (b->flow_quantum * quantum_div[host_load] +
+				  (prandom_u32() >> 16)) >> 16;
+		list_move_tail(&flow->flowchain, &b->old_flows);
+
+		/* Keep all flows with deficits out of the sparse and decaying
+		 * rotations.  No non-empty flow can go into the decaying
+		 * rotation, so they can't get deficits
+		 */
+		if (flow->set == CAKE_SET_SPARSE) {
+			if (flow->head) {
+				b->sparse_flow_count--;
+				b->bulk_flow_count++;
+				flow->set = CAKE_SET_BULK;
+			} else {
+				/* we've moved it to the bulk rotation for
+				 * correct deficit accounting but we still want
+				 * to count it as a sparse flow, not a bulk one.
+				 */
+				flow->set = CAKE_SET_SPARSE_WAIT;
+			}
+		}
+		goto retry;
+	}
+
+	/* Retrieve a packet via the AQM */
+	while (1) {
+		skb = cake_dequeue_one(sch);
+		if (!skb) {
+			/* this queue was actually empty */
+			if (cobalt_queue_empty(&flow->cvars, &b->cparams, now))
+				b->unresponsive_flow_count--;
+
+			if (flow->cvars.p_drop || flow->cvars.count ||
+			    ktime_before(now, flow->cvars.drop_next)) {
+				/* keep in the flowchain until the state has
+				 * decayed to rest
+				 */
+				list_move_tail(&flow->flowchain,
+					       &b->decaying_flows);
+				if (flow->set == CAKE_SET_BULK) {
+					b->bulk_flow_count--;
+					b->decaying_flow_count++;
+				} else if (flow->set == CAKE_SET_SPARSE ||
+					   flow->set == CAKE_SET_SPARSE_WAIT) {
+					b->sparse_flow_count--;
+					b->decaying_flow_count++;
+				}
+				flow->set = CAKE_SET_DECAYING;
+			} else {
+				/* remove empty queue from the flowchain */
+				list_del_init(&flow->flowchain);
+				if (flow->set == CAKE_SET_SPARSE ||
+				    flow->set == CAKE_SET_SPARSE_WAIT)
+					b->sparse_flow_count--;
+				else if (flow->set == CAKE_SET_BULK)
+					b->bulk_flow_count--;
+				else
+					b->decaying_flow_count--;
+
+				flow->set = CAKE_SET_NONE;
+				srchost->srchost_refcnt--;
+				dsthost->dsthost_refcnt--;
+			}
+			goto begin;
+		}
+
+		/* Last packet in queue may be marked, shouldn't be dropped */
+		if (!cobalt_should_drop(&flow->cvars, &b->cparams, now, skb) ||
+		    !flow->head)
+			break;
+
+		flow->dropped++;
+		b->tin_dropped++;
+		qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(skb));
+		qdisc_qstats_drop(sch);
+		kfree_skb(skb);
+	}
+
+	b->tin_ecn_mark += !!flow->cvars.ecn_marked;
+	qdisc_bstats_update(sch, skb);
+
+	/* collect delay stats */
+	delay = ktime_to_ns(ktime_sub(now, cobalt_get_enqueue_time(skb)));
+	b->avge_delay = cake_ewma(b->avge_delay, delay, 8);
+	b->peak_delay = cake_ewma(b->peak_delay, delay,
+				  delay > b->peak_delay ? 2 : 8);
+	b->base_delay = cake_ewma(b->base_delay, delay,
+				  delay < b->base_delay ? 2 : 8);
+
+	len = cake_advance_shaper(q, b, skb, now, false);
+	flow->deficit -= len;
+	b->tin_deficit -= len;
+
+	if (ktime_after(q->time_next_packet, now) && sch->q.qlen) {
+		u64 next = min(ktime_to_ns(q->time_next_packet),
+			       ktime_to_ns(q->failsafe_next_packet));
+
+		qdisc_watchdog_schedule_ns(&q->watchdog, next);
+	} else if (!sch->q.qlen) {
+		int i;
+
+		for (i = 0; i < q->tin_cnt; i++) {
+			if (q->tins[i].decaying_flow_count) {
+				ktime_t next = \
+					ktime_add_ns(now,
+						     q->tins[i].cparams.target);
+
+				qdisc_watchdog_schedule_ns(&q->watchdog,
+							   ktime_to_ns(next));
+				break;
+			}
+		}
+	}
+
+	if (q->overflow_timeout)
+		q->overflow_timeout--;
+
+	return skb;
+}
+
+static void cake_reset(struct Qdisc *sch)
+{
+	u32 c;
+
+	for (c = 0; c < CAKE_MAX_TINS; c++)
+		cake_clear_tin(sch, c);
+}
+
+static const struct nla_policy cake_policy[TCA_CAKE_MAX + 1] = {
+	[TCA_CAKE_BASE_RATE64]   = { .type = NLA_U64 },
+	[TCA_CAKE_DIFFSERV_MODE] = { .type = NLA_U32 },
+	[TCA_CAKE_ATM]		 = { .type = NLA_U32 },
+	[TCA_CAKE_FLOW_MODE]     = { .type = NLA_U32 },
+	[TCA_CAKE_OVERHEAD]      = { .type = NLA_S32 },
+	[TCA_CAKE_RTT]		 = { .type = NLA_U32 },
+	[TCA_CAKE_TARGET]	 = { .type = NLA_U32 },
+	[TCA_CAKE_AUTORATE]      = { .type = NLA_U32 },
+	[TCA_CAKE_MEMORY]	 = { .type = NLA_U32 },
+	[TCA_CAKE_NAT]		 = { .type = NLA_U32 },
+	[TCA_CAKE_RAW]		 = { .type = NLA_U32 },
+	[TCA_CAKE_WASH]		 = { .type = NLA_U32 },
+	[TCA_CAKE_MPU]		 = { .type = NLA_U32 },
+	[TCA_CAKE_INGRESS]	 = { .type = NLA_U32 },
+	[TCA_CAKE_ACK_FILTER]	 = { .type = NLA_U32 },
+};
+
+static void cake_set_rate(struct cake_tin_data *b, u64 rate, u32 mtu,
+			  u64 target_ns, u64 rtt_est_ns)
+{
+	/* convert byte-rate into time-per-byte
+	 * so it will always unwedge in reasonable time.
+	 */
+	static const u64 MIN_RATE = 64;
+	u32 byte_target = mtu;
+	u64 byte_target_ns;
+	u8  rate_shft = 0;
+	u64 rate_ns = 0;
+
+	b->flow_quantum = 1514;
+	if (rate) {
+		b->flow_quantum = max(min(rate >> 12, 1514ULL), 300ULL);
+		rate_shft = 34;
+		rate_ns = ((u64)NSEC_PER_SEC) << rate_shft;
+		rate_ns = div64_u64(rate_ns, max(MIN_RATE, rate));
+		while (!!(rate_ns >> 34)) {
+			rate_ns >>= 1;
+			rate_shft--;
+		}
+	} /* else unlimited, ie. zero delay */
+
+	b->tin_rate_bps  = rate;
+	b->tin_rate_ns   = rate_ns;
+	b->tin_rate_shft = rate_shft;
+
+	byte_target_ns = (byte_target * rate_ns) >> rate_shft;
+
+	b->cparams.target = max((byte_target_ns * 3) / 2, target_ns);
+	b->cparams.interval = max(rtt_est_ns +
+				     b->cparams.target - target_ns,
+				     b->cparams.target * 2);
+	b->cparams.mtu_time = byte_target_ns;
+	b->cparams.p_inc = 1 << 24; /* 1/256 */
+	b->cparams.p_dec = 1 << 20; /* 1/4096 */
+}
+
+static void cake_reconfigure(struct Qdisc *sch)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	struct cake_tin_data *b = &q->tins[0];
+	int c, ft = 0;
+
+	q->tin_cnt = 1;
+	cake_set_rate(b, q->rate_bps, psched_mtu(qdisc_dev(sch)),
+		      us_to_ns(q->target), us_to_ns(q->interval));
+	b->tin_quantum_band = 65535;
+	b->tin_quantum_prio = 65535;
+
+	for (c = q->tin_cnt; c < CAKE_MAX_TINS; c++) {
+		cake_clear_tin(sch, c);
+		q->tins[c].cparams.mtu_time = q->tins[ft].cparams.mtu_time;
+	}
+
+	q->rate_ns   = q->tins[ft].tin_rate_ns;
+	q->rate_shft = q->tins[ft].tin_rate_shft;
+
+	if (q->buffer_config_limit) {
+		q->buffer_limit = q->buffer_config_limit;
+	} else if (q->rate_bps) {
+		u64 t = q->rate_bps * q->interval;
+
+		do_div(t, USEC_PER_SEC / 4);
+		q->buffer_limit = max_t(u32, t, 4U << 20);
+	} else {
+		q->buffer_limit = ~0;
+	}
+
+	sch->flags &= ~TCQ_F_CAN_BYPASS;
+
+	q->buffer_limit = min(q->buffer_limit,
+			      max(sch->limit * psched_mtu(qdisc_dev(sch)),
+				  q->buffer_config_limit));
+}
+
+static int cake_change(struct Qdisc *sch, struct nlattr *opt,
+		       struct netlink_ext_ack *extack)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	struct nlattr *tb[TCA_CAKE_MAX + 1];
+	int err;
+
+	if (!opt)
+		return -EINVAL;
+
+	err = nla_parse_nested(tb, TCA_CAKE_MAX, opt, cake_policy, extack);
+	if (err < 0)
+		return err;
+
+	if (tb[TCA_CAKE_BASE_RATE64])
+		q->rate_bps = nla_get_u64(tb[TCA_CAKE_BASE_RATE64]);
+
+	if (tb[TCA_CAKE_FLOW_MODE])
+		q->flow_mode = (nla_get_u32(tb[TCA_CAKE_FLOW_MODE]) &
+				CAKE_FLOW_MASK);
+
+	if (tb[TCA_CAKE_RTT]) {
+		q->interval = nla_get_u32(tb[TCA_CAKE_RTT]);
+
+		if (!q->interval)
+			q->interval = 1;
+	}
+
+	if (tb[TCA_CAKE_TARGET]) {
+		q->target = nla_get_u32(tb[TCA_CAKE_TARGET]);
+
+		if (!q->target)
+			q->target = 1;
+	}
+
+	if (tb[TCA_CAKE_MEMORY])
+		q->buffer_config_limit = nla_get_u32(tb[TCA_CAKE_MEMORY]);
+
+	if (q->tins) {
+		sch_tree_lock(sch);
+		cake_reconfigure(sch);
+		sch_tree_unlock(sch);
+	}
+
+	return 0;
+}
+
+static void cake_destroy(struct Qdisc *sch)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+
+	qdisc_watchdog_cancel(&q->watchdog);
+	tcf_block_put(q->block);
+	kvfree(q->tins);
+}
+
+static int cake_init(struct Qdisc *sch, struct nlattr *opt,
+		     struct netlink_ext_ack *extack)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	int i, j, err;
+
+	sch->limit = 10240;
+	q->tin_mode = CAKE_DIFFSERV_BESTEFFORT;
+	q->flow_mode  = CAKE_FLOW_TRIPLE;
+
+	q->rate_bps = 0; /* unlimited by default */
+
+	q->interval = 100000; /* 100ms default */
+	q->target   =   5000; /* 5ms: codel RFC argues
+			       * for 5 to 10% of interval
+			       */
+
+	q->cur_tin = 0;
+	q->cur_flow  = 0;
+
+	qdisc_watchdog_init(&q->watchdog, sch);
+
+	if (opt) {
+		int err = cake_change(sch, opt, extack);
+
+		if (err)
+			return err;
+	}
+
+	err = tcf_block_get(&q->block, &q->filter_list, sch, extack);
+	if (err)
+		return err;
+
+	quantum_div[0] = ~0;
+	for (i = 1; i <= CAKE_QUEUES; i++)
+		quantum_div[i] = 65535 / i;
+
+	q->tins = kvzalloc(CAKE_MAX_TINS * sizeof(struct cake_tin_data),
+			   GFP_KERNEL);
+	if (!q->tins)
+		goto nomem;
+
+	for (i = 0; i < CAKE_MAX_TINS; i++) {
+		struct cake_tin_data *b = q->tins + i;
+
+		INIT_LIST_HEAD(&b->new_flows);
+		INIT_LIST_HEAD(&b->old_flows);
+		INIT_LIST_HEAD(&b->decaying_flows);
+		b->sparse_flow_count = 0;
+		b->bulk_flow_count = 0;
+		b->decaying_flow_count = 0;
+
+		for (j = 0; j < CAKE_QUEUES; j++) {
+			struct cake_flow *flow = b->flows + j;
+			u32 k = j * CAKE_MAX_TINS + i;
+
+			INIT_LIST_HEAD(&flow->flowchain);
+			cobalt_vars_init(&flow->cvars);
+
+			q->overflow_heap[k].t = i;
+			q->overflow_heap[k].b = j;
+			b->overflow_idx[j] = k;
+		}
+	}
+
+	cake_reconfigure(sch);
+	q->avg_peak_bandwidth = q->rate_bps;
+	q->min_netlen = ~0;
+	q->min_adjlen = ~0;
+	return 0;
+
+nomem:
+	cake_destroy(sch);
+	return -ENOMEM;
+}
+
+static int cake_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	struct nlattr *opts;
+
+	opts = nla_nest_start(skb, TCA_OPTIONS);
+	if (!opts)
+		goto nla_put_failure;
+
+	if (nla_put_u64_64bit(skb, TCA_CAKE_BASE_RATE64, q->rate_bps,
+			      TCA_CAKE_PAD))
+		goto nla_put_failure;
+
+	if (nla_put_u32(skb, TCA_CAKE_FLOW_MODE,
+			q->flow_mode & CAKE_FLOW_MASK))
+		goto nla_put_failure;
+
+	if (nla_put_u32(skb, TCA_CAKE_RTT, q->interval))
+		goto nla_put_failure;
+
+	if (nla_put_u32(skb, TCA_CAKE_TARGET, q->target))
+		goto nla_put_failure;
+
+	if (nla_put_u32(skb, TCA_CAKE_MEMORY, q->buffer_config_limit))
+		goto nla_put_failure;
+
+	return nla_nest_end(skb, opts);
+
+nla_put_failure:
+	return -1;
+}
+
+static int cake_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
+{
+	struct nlattr *stats = nla_nest_start(d->skb, TCA_STATS_APP);
+	struct cake_sched_data *q = qdisc_priv(sch);
+	struct nlattr *tstats, *ts;
+	int i;
+
+	if (!stats)
+		return -1;
+
+#define PUT_STAT_U32(attr, data) do {				       \
+		if (nla_put_u32(d->skb, TCA_CAKE_STATS_ ## attr, data)) \
+			goto nla_put_failure;			       \
+	} while (0)
+#define PUT_STAT_U64(attr, data) do {				       \
+		if (nla_put_u64_64bit(d->skb, TCA_CAKE_STATS_ ## attr, \
+					data, TCA_CAKE_STATS_PAD)) \
+			goto nla_put_failure;			       \
+	} while (0)
+
+	PUT_STAT_U64(CAPACITY_ESTIMATE64, q->avg_peak_bandwidth);
+	PUT_STAT_U32(MEMORY_LIMIT, q->buffer_limit);
+	PUT_STAT_U32(MEMORY_USED, q->buffer_max_used);
+	PUT_STAT_U32(AVG_NETOFF, ((q->avg_netoff + 0x8000) >> 16));
+	PUT_STAT_U32(MAX_NETLEN, q->max_netlen);
+	PUT_STAT_U32(MAX_ADJLEN, q->max_adjlen);
+	PUT_STAT_U32(MIN_NETLEN, q->min_netlen);
+	PUT_STAT_U32(MIN_ADJLEN, q->min_adjlen);
+
+#undef PUT_STAT_U32
+#undef PUT_STAT_U64
+
+	tstats = nla_nest_start(d->skb, TCA_CAKE_STATS_TIN_STATS);
+	if (!tstats)
+		goto nla_put_failure;
+
+#define PUT_TSTAT_U32(attr, data) do {					\
+		if (nla_put_u32(d->skb, TCA_CAKE_TIN_STATS_ ## attr, data)) \
+			goto nla_put_failure;				\
+	} while (0)
+#define PUT_TSTAT_U64(attr, data) do {					\
+		if (nla_put_u64_64bit(d->skb, TCA_CAKE_TIN_STATS_ ## attr, \
+					data, TCA_CAKE_TIN_STATS_PAD))	\
+			goto nla_put_failure;				\
+	} while (0)
+
+	for (i = 0; i < q->tin_cnt; i++) {
+		struct cake_tin_data *b = &q->tins[i];
+
+		ts = nla_nest_start(d->skb, i + 1);
+		if (!ts)
+			goto nla_put_failure;
+
+		PUT_TSTAT_U64(THRESHOLD_RATE64, b->tin_rate_bps);
+		PUT_TSTAT_U64(SENT_BYTES64, b->bytes);
+		PUT_TSTAT_U32(BACKLOG_BYTES, b->tin_backlog);
+
+		PUT_TSTAT_U32(TARGET_US,
+			      ktime_to_us(ns_to_ktime(b->cparams.target)));
+		PUT_TSTAT_U32(INTERVAL_US,
+			      ktime_to_us(ns_to_ktime(b->cparams.interval)));
+
+		PUT_TSTAT_U32(SENT_PACKETS, b->packets);
+		PUT_TSTAT_U32(DROPPED_PACKETS, b->tin_dropped);
+		PUT_TSTAT_U32(ECN_MARKED_PACKETS, b->tin_ecn_mark);
+		PUT_TSTAT_U32(ACKS_DROPPED_PACKETS, b->ack_drops);
+
+		PUT_TSTAT_U32(PEAK_DELAY_US,
+			      ktime_to_us(ns_to_ktime(b->peak_delay)));
+		PUT_TSTAT_U32(AVG_DELAY_US,
+			      ktime_to_us(ns_to_ktime(b->avge_delay)));
+		PUT_TSTAT_U32(BASE_DELAY_US,
+			      ktime_to_us(ns_to_ktime(b->base_delay)));
+
+		PUT_TSTAT_U32(WAY_INDIRECT_HITS, b->way_hits);
+		PUT_TSTAT_U32(WAY_MISSES, b->way_misses);
+		PUT_TSTAT_U32(WAY_COLLISIONS, b->way_collisions);
+
+		PUT_TSTAT_U32(SPARSE_FLOWS, b->sparse_flow_count +
+					    b->decaying_flow_count);
+		PUT_TSTAT_U32(BULK_FLOWS, b->bulk_flow_count);
+		PUT_TSTAT_U32(UNRESPONSIVE_FLOWS, b->unresponsive_flow_count);
+		PUT_TSTAT_U32(MAX_SKBLEN, b->max_skblen);
+
+		PUT_TSTAT_U32(FLOW_QUANTUM, b->flow_quantum);
+		nla_nest_end(d->skb, ts);
+	}
+
+#undef PUT_TSTAT_U32
+#undef PUT_TSTAT_U64
+
+	nla_nest_end(d->skb, tstats);
+	return nla_nest_end(d->skb, stats);
+
+nla_put_failure:
+	nla_nest_cancel(d->skb, stats);
+	return -1;
+}
+
+static struct Qdisc *cake_leaf(struct Qdisc *sch, unsigned long arg)
+{
+	return NULL;
+}
+
+static unsigned long cake_find(struct Qdisc *sch, u32 classid)
+{
+	return 0;
+}
+
+static unsigned long cake_bind(struct Qdisc *sch, unsigned long parent,
+			       u32 classid)
+{
+	return 0;
+}
+
+static void cake_unbind(struct Qdisc *q, unsigned long cl)
+{
+}
+
+static struct tcf_block *cake_tcf_block(struct Qdisc *sch, unsigned long cl,
+					struct netlink_ext_ack *extack)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+
+	if (cl)
+		return NULL;
+	return q->block;
+}
+
+static int cake_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 cake_dump_class_stats(struct Qdisc *sch, unsigned long cl,
+				 struct gnet_dump *d)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	const struct cake_flow *flow = NULL;
+	struct gnet_stats_queue qs = { 0 };
+	struct nlattr *stats;
+	u32 idx = cl - 1;
+
+	if (idx < CAKE_QUEUES * q->tin_cnt) {
+		const struct cake_tin_data *b = &q->tins[idx / CAKE_QUEUES];
+		const struct sk_buff *skb;
+
+		flow = &b->flows[idx % CAKE_QUEUES];
+
+		if (flow->head) {
+			sch_tree_lock(sch);
+			skb = flow->head;
+			while (skb) {
+				qs.qlen++;
+				skb = skb->next;
+			}
+			sch_tree_unlock(sch);
+		}
+		qs.backlog = b->backlogs[idx % CAKE_QUEUES];
+		qs.drops = flow->dropped;
+	}
+	if (gnet_stats_copy_queue(d, NULL, &qs, qs.qlen) < 0)
+		return -1;
+	if (flow) {
+		ktime_t now = ktime_get();
+
+		stats = nla_nest_start(d->skb, TCA_STATS_APP);
+		if (!stats)
+			return -1;
+
+#define PUT_STAT_U32(attr, data) do {				       \
+		if (nla_put_u32(d->skb, TCA_CAKE_STATS_ ## attr, data)) \
+			goto nla_put_failure;			       \
+	} while (0)
+#define PUT_STAT_S32(attr, data) do {				       \
+		if (nla_put_s32(d->skb, TCA_CAKE_STATS_ ## attr, data)) \
+			goto nla_put_failure;			       \
+	} while (0)
+
+		PUT_STAT_S32(DEFICIT, flow->deficit);
+		PUT_STAT_U32(DROPPING, flow->cvars.dropping);
+		PUT_STAT_U32(COBALT_COUNT, flow->cvars.count);
+		PUT_STAT_U32(P_DROP, flow->cvars.p_drop);
+		if (flow->cvars.p_drop) {
+			PUT_STAT_S32(BLUE_TIMER_US,
+				     ktime_to_us(
+					     ktime_sub(now,
+						     flow->cvars.blue_timer)));
+		}
+		if (flow->cvars.dropping) {
+			PUT_STAT_S32(DROP_NEXT_US,
+				     ktime_to_us(
+					     ktime_sub(now,
+						       flow->cvars.drop_next)));
+		}
+
+		if (nla_nest_end(d->skb, stats) < 0)
+			return -1;
+	}
+
+	return 0;
+
+nla_put_failure:
+	nla_nest_cancel(d->skb, stats);
+	return -1;
+}
+
+static void cake_walk(struct Qdisc *sch, struct qdisc_walker *arg)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	unsigned int i, j;
+
+	if (arg->stop)
+		return;
+
+	for (i = 0; i < q->tin_cnt; i++) {
+		struct cake_tin_data *b = &q->tins[i];
+
+		for (j = 0; j < CAKE_QUEUES; j++) {
+			if (list_empty(&b->flows[j].flowchain) ||
+			    arg->count < arg->skip) {
+				arg->count++;
+				continue;
+			}
+			if (arg->fn(sch, i * CAKE_QUEUES + j + 1, arg) < 0) {
+				arg->stop = 1;
+				break;
+			}
+			arg->count++;
+		}
+	}
+}
+
+static const struct Qdisc_class_ops cake_class_ops = {
+	.leaf		=	cake_leaf,
+	.find		=	cake_find,
+	.tcf_block	=	cake_tcf_block,
+	.bind_tcf	=	cake_bind,
+	.unbind_tcf	=	cake_unbind,
+	.dump		=	cake_dump_class,
+	.dump_stats	=	cake_dump_class_stats,
+	.walk		=	cake_walk,
+};
+
+static struct Qdisc_ops cake_qdisc_ops __read_mostly = {
+	.cl_ops		=	&cake_class_ops,
+	.id		=	"cake",
+	.priv_size	=	sizeof(struct cake_sched_data),
+	.enqueue	=	cake_enqueue,
+	.dequeue	=	cake_dequeue,
+	.peek		=	qdisc_peek_dequeued,
+	.init		=	cake_init,
+	.reset		=	cake_reset,
+	.destroy	=	cake_destroy,
+	.change		=	cake_change,
+	.dump		=	cake_dump,
+	.dump_stats	=	cake_dump_stats,
+	.owner		=	THIS_MODULE,
+};
+
+static int __init cake_module_init(void)
+{
+	return register_qdisc(&cake_qdisc_ops);
+}
+
+static void __exit cake_module_exit(void)
+{
+	unregister_qdisc(&cake_qdisc_ops);
+}
+
+module_init(cake_module_init)
+module_exit(cake_module_exit)
+MODULE_AUTHOR("Jonathan Morton");
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_DESCRIPTION("The CAKE shaper.");