sch_cake.c

/*
 * COMMON Applications Kept Enhanced (CAKE) discipline - version 3
 *
 * Copyright (C) 2014-2015 Jonathan Morton <chromatix99@gmail.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *	notice, this list of conditions, and the following disclaimer,
 *	without modification.
 * 2. Redistributions in binary form must reproduce the above copyright
 *	notice, this list of conditions and the following disclaimer in the
 *	documentation and/or other materials provided with the distribution.
 * 3. The names of the authors may not be used to endorse or promote products
 *	derived from this software without specific prior written permission.
 *
 * Alternatively, provided that this notice is retained in full, this
 * software may be distributed under the terms of the GNU General
 * Public License ("GPL") version 2, in which case the provisions of the
 * GPL apply INSTEAD OF those given above.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 *
 */

#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 "pkt_sched.h"
#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 2, 0)
#include <net/flow_keys.h>
#else
#include <net/flow_dissector.h>
#endif
#include "codel5.h"

/* 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 Codel.  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 incorporates much of Eric Dumazet's fq_codel code, which
 * he kindly granted us permission to use, which we customised for use as an
 * integrated subordinate.  See sch_fq_codel.c for details of
 * operation.
 */

#define CAKE_MAX_TINS (8)

#ifndef CAKE_VERSION
#define CAKE_VERSION "unknown"
#endif
static char *cake_version __attribute__((used)) = "Cake version: "
		CAKE_VERSION;

struct cake_flow {
	struct sk_buff	  *head;
	struct sk_buff	  *tail;
	struct list_head  flowchain;
	s32		  deficit;
	u32		  dropped; /* Drops (or ECN marks) on this flow */
	struct codel_vars cvars;
}; /* please try to keep this structure <= 64 bytes */

struct cake_tin_data {
	struct cake_flow *flows;/* Flows table [flows_cnt] */
	u32	*backlogs;	/* backlog table [flows_cnt] */
	u32	 flows_cnt;	/* number of flows - must be multiple of
				 * CAKE_SET_WAYS
				 */
	u32	perturbation;/* hash perturbation */
	u16	quantum;	/* psched_mtu(qdisc_dev(sch)); */
	u16	bulk_flow_count;

	u32	drop_overlimit;

	struct list_head new_flows; /* list of new flows */
	struct list_head old_flows; /* list of old flows */

	/* time_next = time_this + ((len * rate_ns) >> rate_shft) */
	u64	tin_time_next_packet;
	u32	tin_rate_ns;
	u32	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;
}; /* number of tins is small, so size of this struct doesn't matter much */

struct cake_sched_data {
	struct cake_tin_data *tins;
	struct codel_params cparams;
	u16		tin_cnt;
	u8		tin_mode;
	u8		flow_mode;

	/* time_next = time_this + ((len * rate_ns) >> rate_shft) */
	u16		rate_shft;
	u64		time_next_packet;
	u32		rate_ns;
	u32		rate_bps;
	u16		rate_flags;
	s16		rate_overhead;
	u32		interval;
	u32		target;

	/* resource tracking */
	u32		buffer_used;
	u32		buffer_limit;
	u32		buffer_config_limit;

	/* indices for dequeue */
	u16		cur_tin;
	u16		cur_flow;

	struct qdisc_watchdog watchdog;
	u8		tin_index[64];

};

enum {
	CAKE_MODE_BESTEFFORT = 1,
	CAKE_MODE_PRECEDENCE,
	CAKE_MODE_DIFFSERV8,
	CAKE_MODE_DIFFSERV4,
	CAKE_MODE_MAX
};

enum {
	CAKE_FLAG_ATM = 0x0001,
	CAKE_FLAG_AUTORATE_INGRESS = 0x0010,
	CAKE_FLAG_WASH = 0x0100
};

enum {
	CAKE_FLOW_NONE = 0,
	CAKE_FLOW_SRC_IP,
	CAKE_FLOW_DST_IP,
	CAKE_FLOW_HOSTS,    /* = CAKE_FLOW_SRC_IP | CAKE_FLOW_DST_IP */
	CAKE_FLOW_FLOWS,
	CAKE_FLOW_DUAL_SRC, /* = CAKE_FLOW_SRC_IP | CAKE_FLOW_FLOWS */
	CAKE_FLOW_DUAL_DST, /* = CAKE_FLOW_DST_IP | CAKE_FLOW_FLOWS */
	CAKE_FLOW_DUAL,     /* = CAKE_FLOW_HOSTS  | CAKE_FLOW_FLOWS */
	CAKE_FLOW_MAX
};

static inline u32
cake_hash(struct cake_tin_data *q, const struct sk_buff *skb, int flow_mode)
{
#if KERNEL_VERSION(4, 2, 0) > LINUX_VERSION_CODE
	struct flow_keys keys;
#else
	struct flow_keys keys, host_keys;
#endif
	u32 flow_hash, reduced_hash;

	if (unlikely(flow_mode == CAKE_FLOW_NONE))
		return 0;

#if KERNEL_VERSION(4, 2, 0) > LINUX_VERSION_CODE
	skb_flow_dissect(skb, &keys);

	flow_hash = jhash_3words(
		(__force u32)((flow_mode & CAKE_FLOW_DST_IP) ? keys.dst : 0),
		(__force u32)((flow_mode & CAKE_FLOW_SRC_IP) ? keys.src : 0),
		(__force u32)0, q->perturbation);

#else

/* Linux kernel 4.2.x have skb_flow_dissect_flow_keys which takes only 2
 * arguments
 */
#if (KERNEL_VERSION(4, 2, 0) <= LINUX_VERSION_CODE) && (KERNEL_VERSION(4, 3, 0) >  LINUX_VERSION_CODE)
	skb_flow_dissect_flow_keys(skb, &keys);
#else
	skb_flow_dissect_flow_keys(skb, &keys,
				FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
#endif
	flow_hash = flow_hash_from_keys(&keys);
#endif
	reduced_hash = reciprocal_scale(flow_hash, q->flows_cnt);
	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 inline struct sk_buff *dequeue_head(struct cake_flow *flow)
{
	struct sk_buff *skb = flow->head;

	flow->head = skb->next;
	skb->next = NULL;
	return skb;
}

/* add skb to flow queue (tail add) */

static inline 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 inline u32 cake_overhead(struct cake_sched_data *q, u32 in)
{
	u32 out = in + q->rate_overhead;

	if (q->rate_flags & CAKE_FLAG_ATM) {
		out += 47;
		out /= 48;
		out *= 53;
	}

	return out;
}

static inline codel_time_t cake_ewma(codel_time_t avg, codel_time_t sample,
				     u32 shift)
{
	avg -= avg >> shift;
	avg += sample >> shift;
	return avg;
}

/* FIXME: In terms of speed this is a real hit and could be easily
 *  replaced with tail drop...  BUT it's a slow-path routine.
 */

static unsigned int cake_drop(struct Qdisc *sch)
{
	struct cake_sched_data *q = qdisc_priv(sch);
	struct sk_buff *skb;
	u32 maxbacklog = 0, idx = 0, tin = 0, i, j, len;
	struct cake_tin_data *b;
	struct cake_flow *flow;

	/* Queue is full; check across tins in use and
	 * find the fat flow and drop a packet.
	 */
	for (j = 0; j < q->tin_cnt; j++) {
		b = &q->tins[j];

		list_for_each_entry(flow, &b->old_flows, flowchain) {
			i = flow - b->flows;
			if (b->backlogs[i] > maxbacklog) {
				maxbacklog = b->backlogs[i];
				idx = i;
				tin = j;
			}
		}

		list_for_each_entry(flow, &b->new_flows, flowchain) {
			i = flow - b->flows;
			if (b->backlogs[i] > maxbacklog) {
				maxbacklog = b->backlogs[i];
				idx = i;
				tin = j;
			}
		}
	}

	b = &q->tins[tin];
	flow = &b->flows[idx];
	skb = dequeue_head(flow);
	len = qdisc_pkt_len(skb);

	q->buffer_used      -= skb->truesize;
	b->backlogs[idx]    -= len;
	b->tin_backlog      -= len;
	sch->qstats.backlog -= len;

	b->tin_dropped++;
	sch->qstats.drops++;
	flow->dropped++;

	kfree_skb(skb);
	sch->q.qlen--;

	return idx + (tin << 16);
}

static inline void cake_wash_diffserv(struct sk_buff *skb)
{
	switch (skb->protocol) {
	case htons(ETH_P_IP):
		ipv4_change_dsfield(ip_hdr(skb), INET_ECN_MASK, 0);
		break;
	case htons(ETH_P_IPV6):
		ipv6_change_dsfield(ipv6_hdr(skb), INET_ECN_MASK, 0);
		break;
	default:
		break;
	};
}

static inline u32 cake_handle_diffserv(struct sk_buff *skb, u16 wash)
{
	u32 dscp;

	switch (skb->protocol) {
	case htons(ETH_P_IP):
		dscp = ipv4_get_dsfield(ip_hdr(skb)) >> 2;
		if (wash && dscp)
			ipv4_change_dsfield(ip_hdr(skb), INET_ECN_MASK, 0);
		return dscp;

	case htons(ETH_P_IPV6):
		dscp = ipv6_get_dsfield(ipv6_hdr(skb)) >> 2;
		if (wash && dscp)
			ipv6_change_dsfield(ipv6_hdr(skb), INET_ECN_MASK, 0);
		return dscp;

	default:
		/* If there is no Diffserv field, treat as bulk */
		return 0;
	};
}

static void cake_reconfigure(struct Qdisc *sch);

static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
	struct cake_sched_data *q = qdisc_priv(sch);
	u32 idx, tin;
	struct cake_tin_data *b;
	struct cake_flow *flow;
	u32 len = qdisc_pkt_len(skb);
	u64 now = codel_get_time();

	/* extract the Diffserv Precedence field, if it exists */
	/* and clear DSCP bits if washing */
	if (q->tin_mode != CAKE_MODE_BESTEFFORT) {
		tin = q->tin_index[cake_handle_diffserv(skb,
				q->rate_flags & CAKE_FLAG_WASH)];
		if (unlikely(tin >= q->tin_cnt))
			tin = 0;
	} else {
		tin = 0;
		if (q->rate_flags & CAKE_FLAG_WASH)
			cake_wash_diffserv(skb);
	}

	b = &q->tins[tin];

	/* choose flow to insert into */
	idx = cake_hash(b, skb, q->flow_mode);
	flow = &b->flows[idx];

	/* ensure shaper state isn't stale */
	if (!b->tin_backlog) {
		if (b->tin_time_next_packet < now)
			b->tin_time_next_packet = now;

		if (!sch->q.qlen)
			if (q->time_next_packet < now)
				q->time_next_packet = now;
	}

	/* Split GSO aggregates if they're likely to impair flow isolation
	 * or if we need to know individual packet sizes for framing overhead.
	 */

	if (unlikely(skb_is_gso(skb))) {
		struct sk_buff *segs, *nskb;
		netdev_features_t features = netif_skb_features(skb);
		u32 slen = 0;
		segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);

		if (IS_ERR_OR_NULL(segs))
			return qdisc_reshape_fail(skb, sch);

		while (segs) {
			nskb = segs->next;
			segs->next = NULL;
			qdisc_skb_cb(segs)->pkt_len = segs->len;
			get_codel_cb(segs)->enqueue_time = now;
			flow_queue_add(flow, segs);
			/* stats */
			sch->q.qlen++;
			b->packets++;
			slen += segs->len;
			q->buffer_used      += segs->truesize;
			segs = nskb;
		}

		b->bytes            += slen;
		b->backlogs[idx]    += slen;
		b->tin_backlog      += slen;
		sch->qstats.backlog += slen;

		qdisc_tree_decrease_qlen(sch, 1);
		consume_skb(skb);
	} else {
		/* not splitting */
		get_codel_cb(skb)->enqueue_time = now;
		flow_queue_add(flow, skb);

		/* stats */
		sch->q.qlen++;
		b->packets++;
		b->bytes            += len;
		b->backlogs[idx]    += len;
		b->tin_backlog      += len;
		sch->qstats.backlog += len;
		q->buffer_used      += skb->truesize;
	}

	/* flowchain */
	if (list_empty(&flow->flowchain)) {
		list_add_tail(&flow->flowchain, &b->new_flows);
		flow->deficit = b->quantum;
		flow->dropped = 0;
	}

	if (q->buffer_used > q->buffer_limit) {
		u32  dropped = 0;

		while (q->buffer_used > q->buffer_limit) {
			dropped++;
			cake_drop(sch);
		}
		b->drop_overlimit += dropped;
		qdisc_tree_decrease_qlen(sch, dropped);
	}
	return NET_XMIT_SUCCESS;
}

/* Callback from codel_dequeue(); sch->qstats.backlog is already handled. */
static struct sk_buff *custom_dequeue(struct codel_vars *vars,
				      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;

	/* WARN_ON(flow != container_of(vars, struct cake_flow, cvars)); */

	if (flow->head) {
		skb = dequeue_head(flow);
		len = qdisc_pkt_len(skb);
		b->backlogs[q->cur_flow] -= len;
		b->tin_backlog           -= len;
		q->buffer_used           -= skb->truesize;
		sch->q.qlen--;
	}
	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 cake_tin_data *b = &q->tins[tin];

	q->cur_tin = tin;
	for (q->cur_flow = 0; q->cur_flow < b->flows_cnt; q->cur_flow++)
		while (custom_dequeue(NULL, sch))
			;
}

static struct sk_buff *cake_dequeue(struct Qdisc *sch)
{
	struct cake_sched_data *q = qdisc_priv(sch);
	struct sk_buff *skb;
	struct cake_tin_data *b = &q->tins[q->cur_tin];
	struct cake_flow *flow;
	struct list_head *head;
	u16 prev_drop_count, prev_ecn_mark;
	u32 len;
	codel_time_t now = ktime_get_ns();
	s32 i;

begin:
	if (!sch->q.qlen)
		return NULL;

	/* global hard shaper */
	if (q->time_next_packet > now) {
		sch->qstats.overlimits++;
		codel_watchdog_schedule_ns(&q->watchdog, q->time_next_packet,
					   true);
		return NULL;
	}

	/* Choose a class to work on. */
	while (!b->tin_backlog || b->tin_deficit <= 0) {
		/* this is the priority soft-shaper magic */
		if (b->tin_deficit <= 0)
			b->tin_deficit +=
				b->tin_time_next_packet > now ?
					b->tin_quantum_band :
					b->tin_quantum_prio;

		q->cur_tin++;
		b++;
		if (q->cur_tin >= q->tin_cnt) {
			q->cur_tin = 0;
			b = q->tins;
		}
	}

retry:
	/* service this class */
	head = &b->new_flows;
	if (list_empty(head)) {
		head = &b->old_flows;

		if (unlikely(list_empty(head))) {
			/* shouldn't ever happen */
			WARN_ON(b->tin_backlog);
			b->tin_backlog = 0;
			goto begin;
		}
	}
	flow = list_first_entry(head, struct cake_flow, flowchain);
	q->cur_flow = flow - b->flows;

	if (flow->deficit <= 0) {
		flow->deficit += b->quantum;
		list_move_tail(&flow->flowchain, &b->old_flows);
		if (head == &b->new_flows) {
			b->bulk_flow_count++;
		}
		goto retry;
	}

	prev_drop_count = flow->cvars.drop_count;
	prev_ecn_mark   = flow->cvars.ecn_mark;

	skb = codel_dequeue(sch, &flow->cvars, &q->cparams, now,
			    q->buffer_used >
			    (q->buffer_limit >> 2) + (q->buffer_limit >> 1));

	b->tin_dropped  += flow->cvars.drop_count - prev_drop_count;
	b->tin_ecn_mark += flow->cvars.ecn_mark   - prev_ecn_mark;
	flow->cvars.ecn_mark = 0;
	flow->dropped        += flow->cvars.drop_count - prev_drop_count;

	if (!skb) {
		/* codel dropped the last packet in this queue; try again */
		if ((head == &b->new_flows) &&
		    !list_empty(&b->old_flows)) {
			list_move_tail(&flow->flowchain, &b->old_flows);
			b->bulk_flow_count++;
		} else {
			list_del_init(&flow->flowchain);
			if (!(head == &b->new_flows))
				b->bulk_flow_count--;
		}
		goto begin;
	}

	qdisc_bstats_update(sch, skb);
	if (flow->cvars.drop_count && sch->q.qlen) {
		qdisc_tree_decrease_qlen(sch, flow->cvars.drop_count);
		flow->cvars.drop_count = 0;
	}

	len = cake_overhead(q, qdisc_pkt_len(skb));

	flow->deficit -= len;
	b->tin_deficit -= len;

	/* charge packet bandwidth to this and all lower tins, and
	 * to the global shaper.
	 */
	for (i = q->cur_tin; i >= 0; i--, b--)
		b->tin_time_next_packet +=
			(len * (u64)b->tin_rate_ns) >> b->tin_rate_shft;
	q->time_next_packet += (len * (u64)q->rate_ns) >> q->rate_shft;

	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_RATE]     = { .type = NLA_U32 },
	[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_MEMORY]        = { .type = NLA_U32 },
	[TCA_CAKE_WASH]          = { .type = NLA_U32 },
};

static void cake_set_rate(struct cake_tin_data *b, u64 rate)
{
	/* convert byte-rate into time-per-byte
	 * so it will always unwedge in reasonable time.
	 */
	static const u64 MIN_RATE = 64;
	u64 rate_ns = 0;
	u8  rate_shft = 0;

	if (rate) {
		rate_shft = 32;
		rate_ns = ((u64) NSEC_PER_SEC) << rate_shft;
		do_div(rate_ns, max(MIN_RATE, rate));
		while (!!(rate_ns >> 32)) {
			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;

	b->quantum = max(min(rate >> 12, 1514ULL), 300ULL);
}

static void cake_config_besteffort(struct Qdisc *sch)
{
	struct cake_sched_data *q = qdisc_priv(sch);
	struct cake_tin_data *b = &q->tins[0];
	u64 rate = q->rate_bps;
	u32 i;

	q->tin_cnt = 1;

	for (i = 0; i < 64; i++)
		q->tin_index[i] = 0;

	cake_set_rate(b, rate);
	b->tin_quantum_band = 65535;
	b->tin_quantum_prio = 65535;
}

static void cake_config_precedence(struct Qdisc *sch)
{
	/* convert high-level (user visible) parameters into internal format */
	struct cake_sched_data *q = qdisc_priv(sch);
	u64 rate = q->rate_bps;
	u32 quantum1 = 256;
	u32 quantum2 = 256;
	u32 i;

	q->tin_cnt = 8;

	for (i = 0; i < 64; i++)
		q->tin_index[i] = min((u32)(i >> 3), (u32)(q->tin_cnt));

	for (i = 0; i < q->tin_cnt; i++) {
		struct cake_tin_data *b = &q->tins[i];

		cake_set_rate(b, rate);

		b->tin_quantum_prio = max_t(u16, 1U, quantum1);
		b->tin_quantum_band = max_t(u16, 1U, quantum2);

		/* calculate next class's parameters */
		rate  *= 7;
		rate >>= 3;

		quantum1  *= 3;
		quantum1 >>= 1;

		quantum2  *= 7;
		quantum2 >>= 3;
	}
}

/*	List of known Diffserv codepoints:
 *
 *	Least Effort (CS1)
 *	Best Effort (CS0)
 *	Max Reliability (TOS1)
 *	Max Throughput (TOS2)
 *	Min Delay (TOS4)
 *	Assured Forwarding 1 (AF1x) - x3
 *	Assured Forwarding 2 (AF2x) - x3
 *	Assured Forwarding 3 (AF3x) - x3
 *	Assured Forwarding 4 (AF4x) - x3
 *	Precedence Class 2 (CS2)
 *	Precedence Class 3 (CS3)
 *	Precedence Class 4 (CS4)
 *	Precedence Class 5 (CS5)
 *	Precedence Class 6 (CS6)
 *	Precedence Class 7 (CS7)
 *	Voice Admit (VA)
 *	Expedited Forwarding (EF)

 *	Total 25 codepoints.
 */

/*	List of traffic classes in RFC 4594:
 *		(roughly descending order of contended priority)
 *		(roughly ascending order of uncontended throughput)
 *
 *	Network Control (CS6,CS7)      - routing traffic
 *	Telephony (EF,VA)         - aka. VoIP streams
 *	Signalling (CS5)               - VoIP setup
 *	Multimedia Conferencing (AF4x) - aka. video calls
 *	Realtime Interactive (CS4)     - eg. games
 *	Multimedia Streaming (AF3x)    - eg. YouTube, NetFlix, Twitch
 *	Broadcast Video (CS3)
 *	Low Latency Data (AF2x,TOS4)      - eg. database
 *	Ops, Admin, Management (CS2,TOS1) - eg. ssh
 *	Standard Service (CS0 & unrecognised codepoints)
 *	High Throughput Data (AF1x,TOS2)  - eg. web traffic
 *	Low Priority Data (CS1)           - eg. BitTorrent

 *	Total 12 traffic classes.
 */

static void cake_config_diffserv8(struct Qdisc *sch)
{
/*	Pruned list of traffic classes for typical applications:
 *
 *		Network Control          (CS6, CS7)
 *		Minimum Latency          (EF, VA, CS5, CS4)
 *		Interactive Shell        (CS2, TOS1)
 *		Low Latency Transactions (AF2x, TOS4)
 *		Video Streaming          (AF4x, AF3x, CS3)
 *		Bog Standard             (CS0 etc.)
 *		High Throughput          (AF1x, TOS2)
 *		Background Traffic       (CS1)
 *
 *		Total 8 traffic classes.
*/

	struct cake_sched_data *q = qdisc_priv(sch);
	u64 rate = q->rate_bps;
	u32 quantum1 = 256;
	u32 quantum2 = 256;
	u32 i;

	q->tin_cnt = 8;

	/* codepoint to class mapping */
	for (i = 0; i < 64; i++)
		q->tin_index[i] = 2;	/* default to best-effort */

	q->tin_index[0x08] = 0;	/* CS1 */
	q->tin_index[0x02] = 1;	/* TOS2 */
	q->tin_index[0x18] = 3;	/* CS3 */
	q->tin_index[0x04] = 4;	/* TOS4 */
	q->tin_index[0x01] = 5;	/* TOS1 */
	q->tin_index[0x10] = 5;	/* CS2 */
	q->tin_index[0x20] = 6;	/* CS4 */
	q->tin_index[0x28] = 6;	/* CS5 */
	q->tin_index[0x2c] = 6;	/* VA */
	q->tin_index[0x2e] = 6;	/* EF */
	q->tin_index[0x30] = 7;	/* CS6 */
	q->tin_index[0x38] = 7;	/* CS7 */

	for (i = 2; i <= 6; i += 2) {
		q->tin_index[0x08 + i] = 1;	/* AF1x */
		q->tin_index[0x10 + i] = 4;	/* AF2x */
		q->tin_index[0x18 + i] = 3;	/* AF3x */
		q->tin_index[0x20 + i] = 3;	/* AF4x */
	}

	/* class characteristics */
	for (i = 0; i < q->tin_cnt; i++) {
		struct cake_tin_data *b = &q->tins[i];

		cake_set_rate(b, rate);

		b->tin_quantum_prio = max_t(u16, 1U, quantum1);
		b->tin_quantum_band = max_t(u16, 1U, quantum2);

		/* calculate next class's parameters */
		rate  *= 7;
		rate >>= 3;

		quantum1  *= 3;
		quantum1 >>= 1;

		quantum2  *= 7;
		quantum2 >>= 3;
	}
}

static void cake_config_diffserv4(struct Qdisc *sch)
{
/*  Further pruned list of traffic classes for four-class system:
 *
 *	    Latency Sensitive  (CS7, CS6, EF, VA, CS5, CS4)
 *	    Streaming Media    (AF4x, AF3x, CS3, AF2x, TOS4, CS2, TOS1)
 *	    Best Effort        (CS0, AF1x, TOS2, and those not specified)
 *	    Background Traffic (CS1)
 *
 *		Total 4 traffic classes.
 */

	struct cake_sched_data *q = qdisc_priv(sch);
	u64 rate = q->rate_bps;
	u32 quantum = 256;
	u32 i;

	q->tin_cnt = 4;

	/* codepoint to class mapping */
	for (i = 0; i < 64; i++)
		q->tin_index[i] = 1;	/* default to best-effort */

	q->tin_index[0x08] = 0;	/* CS1 */

	q->tin_index[0x18] = 2;	/* CS3 */
	q->tin_index[0x04] = 2;	/* TOS4 */
	q->tin_index[0x01] = 2;	/* TOS1 */
	q->tin_index[0x10] = 2;	/* CS2 */

	q->tin_index[0x20] = 3;	/* CS4 */
	q->tin_index[0x28] = 3;	/* CS5 */
	q->tin_index[0x2c] = 3;	/* VA */
	q->tin_index[0x2e] = 3;	/* EF */
	q->tin_index[0x30] = 3;	/* CS6 */
	q->tin_index[0x38] = 3;	/* CS7 */

	for (i = 2; i <= 6; i += 2) {
		q->tin_index[0x10 + i] = 2;	/* AF2x */
		q->tin_index[0x18 + i] = 2;	/* AF3x */
		q->tin_index[0x20 + i] = 2;	/* AF4x */
	}

	/* class characteristics */
	cake_set_rate(&q->tins[0], rate);
	cake_set_rate(&q->tins[1], rate - (rate >> 4));
	cake_set_rate(&q->tins[2], rate - (rate >> 2));
	cake_set_rate(&q->tins[3], rate >> 2);

	/* priority weights */
	q->tins[0].tin_quantum_prio = quantum >> 4;
	q->tins[1].tin_quantum_prio = quantum;
	q->tins[2].tin_quantum_prio = quantum << 2;
	q->tins[3].tin_quantum_prio = quantum << 4;

	/* bandwidth-sharing weights */
	q->tins[0].tin_quantum_band = (quantum >> 4);
	q->tins[1].tin_quantum_band = (quantum >> 3) + (quantum >> 4);
	q->tins[2].tin_quantum_band = (quantum >> 1);
	q->tins[3].tin_quantum_band = (quantum >> 2);
}

static void cake_reconfigure(struct Qdisc *sch)
{
	struct cake_sched_data *q = qdisc_priv(sch);
	int c;

	switch (q->tin_mode) {
	case CAKE_MODE_BESTEFFORT:
	default:
		cake_config_besteffort(sch);
		break;

	case CAKE_MODE_PRECEDENCE:
		cake_config_precedence(sch);
		break;

	case CAKE_MODE_DIFFSERV8:
		cake_config_diffserv8(sch);
		break;

	case CAKE_MODE_DIFFSERV4:
		cake_config_diffserv4(sch);
		break;
	};

	BUG_ON(q->tin_cnt > CAKE_MAX_TINS);
	for (c = q->tin_cnt; c < CAKE_MAX_TINS; c++)
		cake_clear_tin(sch, c);

	q->rate_ns   = q->tins[0].tin_rate_ns;
	q->rate_shft = q->tins[0].tin_rate_shft;

	if (q->buffer_config_limit) {
		q->buffer_limit = q->buffer_config_limit;
	} else if (q->rate_bps) {
		u64 t = (u64) q->rate_bps * q->interval;

		do_div(t, USEC_PER_SEC / 4);
		q->buffer_limit = max_t(u32, t, 65536U);

	} else {
		q->buffer_limit = ~0;
	}

	q->cparams.target = max_t(u64,US2TIME(q->target),0);
	q->cparams.interval = US2TIME(q->interval);

	if (q->rate_bps)
		sch->flags &= ~TCQ_F_CAN_BYPASS;
	else
		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 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);
	if (err < 0)
		return err;

	if (tb[TCA_CAKE_BASE_RATE])
		q->rate_bps = nla_get_u32(tb[TCA_CAKE_BASE_RATE]);

	if (tb[TCA_CAKE_DIFFSERV_MODE])
		q->tin_mode = nla_get_u32(tb[TCA_CAKE_DIFFSERV_MODE]);

	if (tb[TCA_CAKE_ATM]) {
		if (!!nla_get_u32(tb[TCA_CAKE_ATM]))
			q->rate_flags |= CAKE_FLAG_ATM;
		else
			q->rate_flags &= ~CAKE_FLAG_ATM;
	}

	if (tb[TCA_CAKE_WASH]) {
		if (!!nla_get_u32(tb[TCA_CAKE_WASH]))
			q->rate_flags |= CAKE_FLAG_WASH;
		else
			q->rate_flags &= ~CAKE_FLAG_WASH;
	}

	if (tb[TCA_CAKE_FLOW_MODE])
		q->flow_mode = nla_get_u32(tb[TCA_CAKE_FLOW_MODE]);

	if (tb[TCA_CAKE_OVERHEAD])
		q->rate_overhead = nla_get_s32(tb[TCA_CAKE_OVERHEAD]);

	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_AUTORATE]) {
		if (!!nla_get_u32(tb[TCA_CAKE_AUTORATE]))
			q->rate_flags |= CAKE_FLAG_AUTORATE_INGRESS;
		else
			q->rate_flags &= ~CAKE_FLAG_AUTORATE_INGRESS;
	}

	if (tb[TCA_CAKE_MEMORY])
		q->buffer_config_limit = nla_get_s32(tb[TCA_CAKE_MEMORY]);

	if (q->tins) {
		sch_tree_lock(sch);
		cake_reconfigure(sch);
		sch_tree_unlock(sch);
	}

	return 0;
}

static void *cake_zalloc(size_t sz)
{
	void *ptr = kzalloc(sz, GFP_KERNEL | __GFP_NOWARN);

	if (!ptr)
		ptr = vzalloc(sz);
	return ptr;
}

static void cake_free(void *addr)
{
	if (addr)
		kvfree(addr);
}

static void cake_destroy(struct Qdisc *sch)
{
	struct cake_sched_data *q = qdisc_priv(sch);

	qdisc_watchdog_cancel(&q->watchdog);

	if (q->tins) {
		u32 i;

		for (i = 0; i < CAKE_MAX_TINS; i++) {
			cake_free(q->tins[i].backlogs);
			cake_free(q->tins[i].flows);
		}
		cake_free(q->tins);
	}
}

static int cake_init(struct Qdisc *sch, struct nlattr *opt)
{
	struct cake_sched_data *q = qdisc_priv(sch);
	int i, j;

	sch->limit = 10240;
	q->tin_mode = CAKE_MODE_DIFFSERV4;
	q->flow_mode  = CAKE_FLOW_FLOWS;

	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;

	if (opt) {
		int err = cake_change(sch, opt);

		if (err)
			return err;
	}

	qdisc_watchdog_init(&q->watchdog, sch);

	q->tins = cake_zalloc(CAKE_MAX_TINS * sizeof(struct cake_tin_data));
	if (!q->tins)
		goto nomem;

	for (i = 0; i < CAKE_MAX_TINS; i++) {
		struct cake_tin_data *b = q->tins + i;

		b->flows_cnt = 1024;
		b->perturbation = prandom_u32();
		INIT_LIST_HEAD(&b->new_flows);
		INIT_LIST_HEAD(&b->old_flows);
		b->bulk_flow_count = 0;
		/* codel_params_init(&b->cparams); */

		b->flows    = cake_zalloc(b->flows_cnt *
					     sizeof(struct cake_flow));
		b->backlogs = cake_zalloc(b->flows_cnt * sizeof(u32));
		if (!b->flows || !b->backlogs)
			goto nomem;

		for (j = 0; j < b->flows_cnt; j++) {
			struct cake_flow *flow = b->flows + j;

			INIT_LIST_HEAD(&flow->flowchain);
			codel_vars_init(&flow->cvars);
		}
	}

	cake_reconfigure(sch);
	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_u32(skb, TCA_CAKE_BASE_RATE, q->rate_bps))
		goto nla_put_failure;

	if (nla_put_u32(skb, TCA_CAKE_DIFFSERV_MODE, q->tin_mode))
		goto nla_put_failure;

	if (nla_put_u32(skb, TCA_CAKE_ATM, !!(q->rate_flags & CAKE_FLAG_ATM)))
		goto nla_put_failure;

	if (nla_put_u32(skb, TCA_CAKE_FLOW_MODE, q->flow_mode))
		goto nla_put_failure;

	if (nla_put_u32(skb, TCA_CAKE_WASH,
			!!(q->rate_flags & CAKE_FLAG_WASH)))
		goto nla_put_failure;

	if (nla_put_u32(skb, TCA_CAKE_OVERHEAD, q->rate_overhead))
		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_AUTORATE,
			!!(q->rate_flags & CAKE_FLAG_AUTORATE_INGRESS)))
		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)
{
	/* reuse fq_codel stats format */
	struct cake_sched_data *q = qdisc_priv(sch);
	struct tc_cake_xstats *st = cake_zalloc(sizeof(*st));
	int i;

	if (!st)
		return -1;

	BUG_ON(q->tin_cnt > TC_CAKE_MAX_TINS);

	st->version = 3;
	st->max_tins = TC_CAKE_MAX_TINS;
	st->tin_cnt = q->tin_cnt;

	for (i = 0; i < q->tin_cnt; i++) {
		struct cake_tin_data *b = &q->tins[i];

		st->threshold_rate[i]     = b->tin_rate_bps;
		st->target_us[i]          = codel_time_to_us(q->cparams.target);
		st->interval_us[i]        =
			codel_time_to_us(q->cparams.interval);

		/* TODO FIXME: add missing aspects of these composite stats */
		st->sent[i].packets       = b->packets;
		st->sent[i].bytes         = b->bytes;
		st->dropped[i].packets    = b->tin_dropped;
		st->ecn_marked[i].packets = b->tin_ecn_mark;
		st->backlog[i].bytes      = b->tin_backlog;

		st->peak_delay_us[i] = 0;
		st->avge_delay_us[i] = 0;
		st->base_delay_us[i] = 0;

		st->way_indirect_hits[i] = 0;
		st->way_misses[i]        = 0;
		st->way_collisions[i]    = 0;

		st->sparse_flows[i]      = 0;
		st->bulk_flows[i]        = b->bulk_flow_count;
		st->last_skblen[i]       = 0;
		st->max_skblen[i]        = 0;
	}
	st->memory_limit      = q->buffer_limit;
	st->memory_used       = 0;

	i = gnet_stats_copy_app(d, st, sizeof(*st));
	cake_free(st);
	return i;
}

static struct Qdisc *cake_leaf(struct Qdisc *sch, unsigned long arg)
{
	return NULL;
}

static unsigned long cake_get(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_put(struct Qdisc *q, unsigned long cl)
{
}

static struct tcf_proto **cake_find_tcf(struct Qdisc *sch, unsigned long cl)
{
	return NULL;
}

static int cake_dump_tin(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)
{
	/* reuse fq_codel stats format */
	struct cake_sched_data *q = qdisc_priv(sch);
	struct cake_tin_data *b = q->tins;
	u32 tin = 0, idx = cl - 1;
	struct gnet_stats_queue qs = {0};
	struct tc_fq_codel_xstats xstats;

	while (tin < q->tin_cnt && idx >= b->flows_cnt) {
		idx -= b->flows_cnt;
		tin++;
		b++;
	}

	if (tin < q->tin_cnt && idx >= b->flows_cnt) {
		const struct cake_flow *flow = &b->flows[idx];
		const struct sk_buff *skb = flow->head;

		memset(&xstats, 0, sizeof(xstats));
		xstats.type = TCA_FQ_CODEL_XSTATS_CLASS;
		xstats.class_stats.deficit = flow->deficit;
		xstats.class_stats.ldelay = 0;
		xstats.class_stats.count = flow->cvars.count;
		xstats.class_stats.lastcount = 0;
		xstats.class_stats.dropping = flow->cvars.dropping;
		if (flow->cvars.dropping) {
			codel_tdiff_t delta = flow->cvars.drop_next -
				codel_get_time();

			xstats.class_stats.drop_next = (delta >= 0) ?
				codel_time_to_us(delta) :
				-codel_time_to_us(-delta);
		}
		while (skb) {
			qs.qlen++;
			skb = skb->next;
		}
		qs.backlog = b->backlogs[idx];
		qs.drops = flow->dropped;
	}
	if (codel_stats_copy_queue(d, NULL, &qs, 0) < 0)
		return -1;
	if (tin < q->tin_cnt && idx >= b->flows_cnt)
		return gnet_stats_copy_app(d, &xstats, sizeof(xstats));
	return 0;
}

static void cake_walk(struct Qdisc *sch, struct qdisc_walker *arg)
{
	struct cake_sched_data *q = qdisc_priv(sch);
	unsigned int i, j, k;

	if (arg->stop)
		return;

	for (j = k = 0; j < q->tin_cnt; j++) {
		struct cake_tin_data *b = &q->tins[j];

		for (i = 0; i < b->flows_cnt; i++, k++) {
			if (list_empty(&b->flows[i].flowchain) ||
			    arg->count < arg->skip) {
				arg->count++;
				continue;
			}
			if (arg->fn(sch, k + 1, arg) < 0) {
				arg->stop = 1;
				break;
			}
			arg->count++;
		}
	}
}

static const struct Qdisc_class_ops cake_class_ops = {
	.leaf		=	cake_leaf,
	.get		=	cake_get,
	.put		=	cake_put,
	.tcf_chain	=	cake_find_tcf,
	.bind_tcf	=	cake_bind,
	.unbind_tcf	=	cake_put,
	.dump		=	cake_dump_tin,
	.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,
	.drop		=	cake_drop,
	.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. Version: " CAKE_VERSION);