net_sched: SFB flow scheduler

This is the Stochastic Fair Blue scheduler, based on work from :

W. Feng, D. Kandlur, D. Saha, K. Shin. Blue: A New Class of Active Queue
Management Algorithms. U. Michigan CSE-TR-387-99, April 1999.

http://www.thefengs.com/wuchang/blue/CSE-TR-387-99.pdf

This implementation is based on work done by Juliusz Chroboczek

General SFB algorithm can be found in figure 14, page 15:

B[l][n] : L x N array of bins (L levels, N bins per level)
enqueue()
Calculate hash function values h{0}, h{1}, .. h{L-1}
Update bins at each level
for i = 0 to L - 1
   if (B[i][h{i}].qlen > bin_size)
      B[i][h{i}].p_mark += p_increment;
   else if (B[i][h{i}].qlen == 0)
      B[i][h{i}].p_mark -= p_decrement;
p_min = min(B[0][h{0}].p_mark ... B[L-1][h{L-1}].p_mark);
if (p_min == 1.0)
    ratelimit();
else
    mark/drop with probabilty p_min;

I did the adaptation of Juliusz code to meet current kernel standards,
and various changes to address previous comments :

http://thread.gmane.org/gmane.linux.network/90225
http://thread.gmane.org/gmane.linux.network/90375

Default flow classifier is the rxhash introduced by RPS in 2.6.35, but
we can use an external flow classifier if wanted.

tc qdisc add dev $DEV parent 1:11 handle 11:  \
        est 0.5sec 2sec sfb limit 128

tc filter add dev $DEV protocol ip parent 11: handle 3 \
        flow hash keys dst divisor 1024

Notes:

1) SFB default child qdisc is pfifo_fast. It can be changed by another
qdisc but a child qdisc MUST not drop a packet previously queued. This
is because SFB needs to handle a dequeued packet in order to maintain
its virtual queue states. pfifo_head_drop or CHOKe should not be used.

2) ECN is enabled by default, unlike RED/CHOKe/GRED

With help from Patrick McHardy & Andi Kleen

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Juliusz Chroboczek <Juliusz.Chroboczek@pps.jussieu.fr>
CC: Stephen Hemminger <shemminger@vyatta.com>
CC: Patrick McHardy <kaber@trash.net>
CC: Andi Kleen <andi@firstfloor.org>
CC: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 721 insertions, 0 deletions

diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index 8c19b6e3201e..a7a5583d4f68 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -126,6 +126,17 @@ config NET_SCH_RED
           To compile this code as a module, choose M here: the
           module will be called sch_red.
 
+config NET_SCH_SFB
+        tristate "Stochastic Fair Blue (SFB)"
+        ---help---
+          Say Y here if you want to use the Stochastic Fair Blue (SFB)
+          packet scheduling algorithm.
+
+          See the top of <file:net/sched/sch_sfb.c> for more details.
+
+          To compile this code as a module, choose M here: the
+          module will be called sch_sfb.
+
 config NET_SCH_SFQ
         tristate "Stochastic Fairness Queueing (SFQ)"
         ---help---
diff --git a/net/sched/Makefile b/net/sched/Makefile
index 06c6cdfd1948..2e77b8dba22e 100644
--- a/net/sched/Makefile
+++ b/net/sched/Makefile
@@ -24,6 +24,7 @@ obj-$(CONFIG_NET_SCH_RED)	+= sch_red.o
 obj-$(CONFIG_NET_SCH_GRED)      += sch_gred.o
 obj-$(CONFIG_NET_SCH_INGRESS)   += sch_ingress.o 
 obj-$(CONFIG_NET_SCH_DSMARK)    += sch_dsmark.o
+obj-$(CONFIG_NET_SCH_SFB)       += sch_sfb.o
 obj-$(CONFIG_NET_SCH_SFQ)       += sch_sfq.o
 obj-$(CONFIG_NET_SCH_TBF)       += sch_tbf.o
 obj-$(CONFIG_NET_SCH_TEQL)      += sch_teql.o
diff --git a/net/sched/sch_sfb.c b/net/sched/sch_sfb.c
new file mode 100644
index 000000000000..0a833d0c1f61
--- /dev/null
+++ b/net/sched/sch_sfb.c
@@ -0,0 +1,709 @@
+/*
+ * net/sched/sch_sfb.c    Stochastic Fair Blue
+ *
+ * Copyright (c) 2008-2011 Juliusz Chroboczek <jch@pps.jussieu.fr>
+ * Copyright (c) 2011 Eric Dumazet <eric.dumazet@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * version 2 as published by the Free Software Foundation.
+ *
+ * W. Feng, D. Kandlur, D. Saha, K. Shin. Blue:
+ * A New Class of Active Queue Management Algorithms.
+ * U. Michigan CSE-TR-387-99, April 1999.
+ *
+ * http://www.thefengs.com/wuchang/blue/CSE-TR-387-99.pdf
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/skbuff.h>
+#include <linux/random.h>
+#include <linux/jhash.h>
+#include <net/ip.h>
+#include <net/pkt_sched.h>
+#include <net/inet_ecn.h>
+
+/*
+ * SFB uses two B[l][n] : L x N arrays of bins (L levels, N bins per level)
+ * This implementation uses L = 8 and N = 16
+ * This permits us to split one 32bit hash (provided per packet by rxhash or
+ * external classifier) into 8 subhashes of 4 bits.
+ */
+#define SFB_BUCKET_SHIFT 4
+#define SFB_NUMBUCKETS  (1 << SFB_BUCKET_SHIFT) /* N bins per Level */
+#define SFB_BUCKET_MASK (SFB_NUMBUCKETS - 1)
+#define SFB_LEVELS      (32 / SFB_BUCKET_SHIFT) /* L */
+
+/* SFB algo uses a virtual queue, named "bin" */
+struct sfb_bucket {
+        u16             qlen; /* length of virtual queue */
+        u16             p_mark; /* marking probability */
+};
+
+/* We use a double buffering right before hash change
+ * (Section 4.4 of SFB reference : moving hash functions)
+ */
+struct sfb_bins {
+        u32               perturbation; /* jhash perturbation */
+        struct sfb_bucket bins[SFB_LEVELS][SFB_NUMBUCKETS];
+};
+
+struct sfb_sched_data {
+        struct Qdisc    *qdisc;
+        struct tcf_proto *filter_list;
+        unsigned long   rehash_interval;
+        unsigned long   warmup_time;    /* double buffering warmup time in jiffies */
+        u32             max;
+        u32             bin_size;       /* maximum queue length per bin */
+        u32             increment;      /* d1 */
+        u32             decrement;      /* d2 */
+        u32             limit;          /* HARD maximal queue length */
+        u32             penalty_rate;
+        u32             penalty_burst;
+        u32             tokens_avail;
+        unsigned long   rehash_time;
+        unsigned long   token_time;
+
+        u8              slot;           /* current active bins (0 or 1) */
+        bool            double_buffering;
+        struct sfb_bins bins[2];
+
+        struct {
+                u32     earlydrop;
+                u32     penaltydrop;
+                u32     bucketdrop;
+                u32     queuedrop;
+                u32     childdrop;      /* drops in child qdisc */
+                u32     marked;         /* ECN mark */
+        } stats;
+};
+
+/*
+ * Each queued skb might be hashed on one or two bins
+ * We store in skb_cb the two hash values.
+ * (A zero value means double buffering was not used)
+ */
+struct sfb_skb_cb {
+        u32 hashes[2];
+};
+
+static inline struct sfb_skb_cb *sfb_skb_cb(const struct sk_buff *skb)
+{
+        BUILD_BUG_ON(sizeof(skb->cb) <
+                sizeof(struct qdisc_skb_cb) + sizeof(struct sfb_skb_cb));
+        return (struct sfb_skb_cb *)qdisc_skb_cb(skb)->data;
+}
+
+/*
+ * If using 'internal' SFB flow classifier, hash comes from skb rxhash
+ * If using external classifier, hash comes from the classid.
+ */
+static u32 sfb_hash(const struct sk_buff *skb, u32 slot)
+{
+        return sfb_skb_cb(skb)->hashes[slot];
+}
+
+/* Probabilities are coded as Q0.16 fixed-point values,
+ * with 0xFFFF representing 65535/65536 (almost 1.0)
+ * Addition and subtraction are saturating in [0, 65535]
+ */
+static u32 prob_plus(u32 p1, u32 p2)
+{
+        u32 res = p1 + p2;
+
+        return min_t(u32, res, SFB_MAX_PROB);
+}
+
+static u32 prob_minus(u32 p1, u32 p2)
+{
+        return p1 > p2 ? p1 - p2 : 0;
+}
+
+static void increment_one_qlen(u32 sfbhash, u32 slot, struct sfb_sched_data *q)
+{
+        int i;
+        struct sfb_bucket *b = &q->bins[slot].bins[0][0];
+
+        for (i = 0; i < SFB_LEVELS; i++) {
+                u32 hash = sfbhash & SFB_BUCKET_MASK;
+
+                sfbhash >>= SFB_BUCKET_SHIFT;
+                if (b[hash].qlen < 0xFFFF)
+                        b[hash].qlen++;
+                b += SFB_NUMBUCKETS; /* next level */
+        }
+}
+
+static void increment_qlen(const struct sk_buff *skb, struct sfb_sched_data *q)
+{
+        u32 sfbhash;
+
+        sfbhash = sfb_hash(skb, 0);
+        if (sfbhash)
+                increment_one_qlen(sfbhash, 0, q);
+
+        sfbhash = sfb_hash(skb, 1);
+        if (sfbhash)
+                increment_one_qlen(sfbhash, 1, q);
+}
+
+static void decrement_one_qlen(u32 sfbhash, u32 slot,
+                               struct sfb_sched_data *q)
+{
+        int i;
+        struct sfb_bucket *b = &q->bins[slot].bins[0][0];
+
+        for (i = 0; i < SFB_LEVELS; i++) {
+                u32 hash = sfbhash & SFB_BUCKET_MASK;
+
+                sfbhash >>= SFB_BUCKET_SHIFT;
+                if (b[hash].qlen > 0)
+                        b[hash].qlen--;
+                b += SFB_NUMBUCKETS; /* next level */
+        }
+}
+
+static void decrement_qlen(const struct sk_buff *skb, struct sfb_sched_data *q)
+{
+        u32 sfbhash;
+
+        sfbhash = sfb_hash(skb, 0);
+        if (sfbhash)
+                decrement_one_qlen(sfbhash, 0, q);
+
+        sfbhash = sfb_hash(skb, 1);
+        if (sfbhash)
+                decrement_one_qlen(sfbhash, 1, q);
+}
+
+static void decrement_prob(struct sfb_bucket *b, struct sfb_sched_data *q)
+{
+        b->p_mark = prob_minus(b->p_mark, q->decrement);
+}
+
+static void increment_prob(struct sfb_bucket *b, struct sfb_sched_data *q)
+{
+        b->p_mark = prob_plus(b->p_mark, q->increment);
+}
+
+static void sfb_zero_all_buckets(struct sfb_sched_data *q)
+{
+        memset(&q->bins, 0, sizeof(q->bins));
+}
+
+/*
+ * compute max qlen, max p_mark, and avg p_mark
+ */
+static u32 sfb_compute_qlen(u32 *prob_r, u32 *avgpm_r, const struct sfb_sched_data *q)
+{
+        int i;
+        u32 qlen = 0, prob = 0, totalpm = 0;
+        const struct sfb_bucket *b = &q->bins[q->slot].bins[0][0];
+
+        for (i = 0; i < SFB_LEVELS * SFB_NUMBUCKETS; i++) {
+                if (qlen < b->qlen)
+                        qlen = b->qlen;
+                totalpm += b->p_mark;
+                if (prob < b->p_mark)
+                        prob = b->p_mark;
+                b++;
+        }
+        *prob_r = prob;
+        *avgpm_r = totalpm / (SFB_LEVELS * SFB_NUMBUCKETS);
+        return qlen;
+}
+
+
+static void sfb_init_perturbation(u32 slot, struct sfb_sched_data *q)
+{
+        q->bins[slot].perturbation = net_random();
+}
+
+static void sfb_swap_slot(struct sfb_sched_data *q)
+{
+        sfb_init_perturbation(q->slot, q);
+        q->slot ^= 1;
+        q->double_buffering = false;
+}
+
+/* Non elastic flows are allowed to use part of the bandwidth, expressed
+ * in "penalty_rate" packets per second, with "penalty_burst" burst
+ */
+static bool sfb_rate_limit(struct sk_buff *skb, struct sfb_sched_data *q)
+{
+        if (q->penalty_rate == 0 || q->penalty_burst == 0)
+                return true;
+
+        if (q->tokens_avail < 1) {
+                unsigned long age = min(10UL * HZ, jiffies - q->token_time);
+
+                q->tokens_avail = (age * q->penalty_rate) / HZ;
+                if (q->tokens_avail > q->penalty_burst)
+                        q->tokens_avail = q->penalty_burst;
+                q->token_time = jiffies;
+                if (q->tokens_avail < 1)
+                        return true;
+        }
+
+        q->tokens_avail--;
+        return false;
+}
+
+static bool sfb_classify(struct sk_buff *skb, struct sfb_sched_data *q,
+                         int *qerr, u32 *salt)
+{
+        struct tcf_result res;
+        int result;
+
+        result = tc_classify(skb, q->filter_list, &res);
+        if (result >= 0) {
+#ifdef CONFIG_NET_CLS_ACT
+                switch (result) {
+                case TC_ACT_STOLEN:
+                case TC_ACT_QUEUED:
+                        *qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
+                case TC_ACT_SHOT:
+                        return false;
+                }
+#endif
+                *salt = TC_H_MIN(res.classid);
+                return true;
+        }
+        return false;
+}
+
+static int sfb_enqueue(struct sk_buff *skb, struct Qdisc *sch)
+{
+
+        struct sfb_sched_data *q = qdisc_priv(sch);
+        struct Qdisc *child = q->qdisc;
+        int i;
+        u32 p_min = ~0;
+        u32 minqlen = ~0;
+        u32 r, slot, salt, sfbhash;
+        int ret = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
+
+        if (q->rehash_interval > 0) {
+                unsigned long limit = q->rehash_time + q->rehash_interval;
+
+                if (unlikely(time_after(jiffies, limit))) {
+                        sfb_swap_slot(q);
+                        q->rehash_time = jiffies;
+                } else if (unlikely(!q->double_buffering && q->warmup_time > 0 &&
+                                    time_after(jiffies, limit - q->warmup_time))) {
+                        q->double_buffering = true;
+                }
+        }
+
+        if (q->filter_list) {
+                /* If using external classifiers, get result and record it. */
+                if (!sfb_classify(skb, q, &ret, &salt))
+                        goto other_drop;
+        } else {
+                salt = skb_get_rxhash(skb);
+        }
+
+        slot = q->slot;
+
+        sfbhash = jhash_1word(salt, q->bins[slot].perturbation);
+        if (!sfbhash)
+                sfbhash = 1;
+        sfb_skb_cb(skb)->hashes[slot] = sfbhash;
+
+        for (i = 0; i < SFB_LEVELS; i++) {
+                u32 hash = sfbhash & SFB_BUCKET_MASK;
+                struct sfb_bucket *b = &q->bins[slot].bins[i][hash];
+
+                sfbhash >>= SFB_BUCKET_SHIFT;
+                if (b->qlen == 0)
+                        decrement_prob(b, q);
+                else if (b->qlen >= q->bin_size)
+                        increment_prob(b, q);
+                if (minqlen > b->qlen)
+                        minqlen = b->qlen;
+                if (p_min > b->p_mark)
+                        p_min = b->p_mark;
+        }
+
+        slot ^= 1;
+        sfb_skb_cb(skb)->hashes[slot] = 0;
+
+        if (unlikely(minqlen >= q->max || sch->q.qlen >= q->limit)) {
+                sch->qstats.overlimits++;
+                if (minqlen >= q->max)
+                        q->stats.bucketdrop++;
+                else
+                        q->stats.queuedrop++;
+                goto drop;
+        }
+
+        if (unlikely(p_min >= SFB_MAX_PROB)) {
+                /* Inelastic flow */
+                if (q->double_buffering) {
+                        sfbhash = jhash_1word(salt, q->bins[slot].perturbation);
+                        if (!sfbhash)
+                                sfbhash = 1;
+                        sfb_skb_cb(skb)->hashes[slot] = sfbhash;
+
+                        for (i = 0; i < SFB_LEVELS; i++) {
+                                u32 hash = sfbhash & SFB_BUCKET_MASK;
+                                struct sfb_bucket *b = &q->bins[slot].bins[i][hash];
+
+                                sfbhash >>= SFB_BUCKET_SHIFT;
+                                if (b->qlen == 0)
+                                        decrement_prob(b, q);
+                                else if (b->qlen >= q->bin_size)
+                                        increment_prob(b, q);
+                        }
+                }
+                if (sfb_rate_limit(skb, q)) {
+                        sch->qstats.overlimits++;
+                        q->stats.penaltydrop++;
+                        goto drop;
+                }
+                goto enqueue;
+        }
+
+        r = net_random() & SFB_MAX_PROB;
+
+        if (unlikely(r < p_min)) {
+                if (unlikely(p_min > SFB_MAX_PROB / 2)) {
+                        /* If we're marking that many packets, then either
+                         * this flow is unresponsive, or we're badly congested.
+                         * In either case, we want to start dropping packets.
+                         */
+                        if (r < (p_min - SFB_MAX_PROB / 2) * 2) {
+                                q->stats.earlydrop++;
+                                goto drop;
+                        }
+                }
+                if (INET_ECN_set_ce(skb)) {
+                        q->stats.marked++;
+                } else {
+                        q->stats.earlydrop++;
+                        goto drop;
+                }
+        }
+
+enqueue:
+        ret = qdisc_enqueue(skb, child);
+        if (likely(ret == NET_XMIT_SUCCESS)) {
+                sch->q.qlen++;
+                increment_qlen(skb, q);
+        } else if (net_xmit_drop_count(ret)) {
+                q->stats.childdrop++;
+                sch->qstats.drops++;
+        }
+        return ret;
+
+drop:
+        qdisc_drop(skb, sch);
+        return NET_XMIT_CN;
+other_drop:
+        if (ret & __NET_XMIT_BYPASS)
+                sch->qstats.drops++;
+        kfree_skb(skb);
+        return ret;
+}
+
+static struct sk_buff *sfb_dequeue(struct Qdisc *sch)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+        struct Qdisc *child = q->qdisc;
+        struct sk_buff *skb;
+
+        skb = child->dequeue(q->qdisc);
+
+        if (skb) {
+                qdisc_bstats_update(sch, skb);
+                sch->q.qlen--;
+                decrement_qlen(skb, q);
+        }
+
+        return skb;
+}
+
+static struct sk_buff *sfb_peek(struct Qdisc *sch)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+        struct Qdisc *child = q->qdisc;
+
+        return child->ops->peek(child);
+}
+
+/* No sfb_drop -- impossible since the child doesn't return the dropped skb. */
+
+static void sfb_reset(struct Qdisc *sch)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+
+        qdisc_reset(q->qdisc);
+        sch->q.qlen = 0;
+        q->slot = 0;
+        q->double_buffering = false;
+        sfb_zero_all_buckets(q);
+        sfb_init_perturbation(0, q);
+}
+
+static void sfb_destroy(struct Qdisc *sch)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+
+        tcf_destroy_chain(&q->filter_list);
+        qdisc_destroy(q->qdisc);
+}
+
+static const struct nla_policy sfb_policy[TCA_SFB_MAX + 1] = {
+        [TCA_SFB_PARMS] = { .len = sizeof(struct tc_sfb_qopt) },
+};
+
+static const struct tc_sfb_qopt sfb_default_ops = {
+        .rehash_interval = 600 * MSEC_PER_SEC,
+        .warmup_time = 60 * MSEC_PER_SEC,
+        .limit = 0,
+        .max = 25,
+        .bin_size = 20,
+        .increment = (SFB_MAX_PROB + 500) / 1000, /* 0.1 % */
+        .decrement = (SFB_MAX_PROB + 3000) / 6000,
+        .penalty_rate = 10,
+        .penalty_burst = 20,
+};
+
+static int sfb_change(struct Qdisc *sch, struct nlattr *opt)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+        struct Qdisc *child;
+        struct nlattr *tb[TCA_SFB_MAX + 1];
+        const struct tc_sfb_qopt *ctl = &sfb_default_ops;
+        u32 limit;
+        int err;
+
+        if (opt) {
+                err = nla_parse_nested(tb, TCA_SFB_MAX, opt, sfb_policy);
+                if (err < 0)
+                        return -EINVAL;
+
+                if (tb[TCA_SFB_PARMS] == NULL)
+                        return -EINVAL;
+
+                ctl = nla_data(tb[TCA_SFB_PARMS]);
+        }
+
+        limit = ctl->limit;
+        if (limit == 0)
+                limit = max_t(u32, qdisc_dev(sch)->tx_queue_len, 1);
+
+        child = fifo_create_dflt(sch, &pfifo_qdisc_ops, limit);
+        if (IS_ERR(child))
+                return PTR_ERR(child);
+
+        sch_tree_lock(sch);
+
+        qdisc_tree_decrease_qlen(q->qdisc, q->qdisc->q.qlen);
+        qdisc_destroy(q->qdisc);
+        q->qdisc = child;
+
+        q->rehash_interval = msecs_to_jiffies(ctl->rehash_interval);
+        q->warmup_time = msecs_to_jiffies(ctl->warmup_time);
+        q->rehash_time = jiffies;
+        q->limit = limit;
+        q->increment = ctl->increment;
+        q->decrement = ctl->decrement;
+        q->max = ctl->max;
+        q->bin_size = ctl->bin_size;
+        q->penalty_rate = ctl->penalty_rate;
+        q->penalty_burst = ctl->penalty_burst;
+        q->tokens_avail = ctl->penalty_burst;
+        q->token_time = jiffies;
+
+        q->slot = 0;
+        q->double_buffering = false;
+        sfb_zero_all_buckets(q);
+        sfb_init_perturbation(0, q);
+        sfb_init_perturbation(1, q);
+
+        sch_tree_unlock(sch);
+
+        return 0;
+}
+
+static int sfb_init(struct Qdisc *sch, struct nlattr *opt)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+
+        q->qdisc = &noop_qdisc;
+        return sfb_change(sch, opt);
+}
+
+static int sfb_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+        struct nlattr *opts;
+        struct tc_sfb_qopt opt = {
+                .rehash_interval = jiffies_to_msecs(q->rehash_interval),
+                .warmup_time = jiffies_to_msecs(q->warmup_time),
+                .limit = q->limit,
+                .max = q->max,
+                .bin_size = q->bin_size,
+                .increment = q->increment,
+                .decrement = q->decrement,
+                .penalty_rate = q->penalty_rate,
+                .penalty_burst = q->penalty_burst,
+        };
+
+        sch->qstats.backlog = q->qdisc->qstats.backlog;
+        opts = nla_nest_start(skb, TCA_OPTIONS);
+        NLA_PUT(skb, TCA_SFB_PARMS, sizeof(opt), &opt);
+        return nla_nest_end(skb, opts);
+
+nla_put_failure:
+        nla_nest_cancel(skb, opts);
+        return -EMSGSIZE;
+}
+
+static int sfb_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+        struct tc_sfb_xstats st = {
+                .earlydrop = q->stats.earlydrop,
+                .penaltydrop = q->stats.penaltydrop,
+                .bucketdrop = q->stats.bucketdrop,
+                .queuedrop = q->stats.queuedrop,
+                .childdrop = q->stats.childdrop,
+                .marked = q->stats.marked,
+        };
+
+        st.maxqlen = sfb_compute_qlen(&st.maxprob, &st.avgprob, q);
+
+        return gnet_stats_copy_app(d, &st, sizeof(st));
+}
+
+static int sfb_dump_class(struct Qdisc *sch, unsigned long cl,
+                          struct sk_buff *skb, struct tcmsg *tcm)
+{
+        return -ENOSYS;
+}
+
+static int sfb_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new,
+                     struct Qdisc **old)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+
+        if (new == NULL)
+                new = &noop_qdisc;
+
+        sch_tree_lock(sch);
+        *old = q->qdisc;
+        q->qdisc = new;
+        qdisc_tree_decrease_qlen(*old, (*old)->q.qlen);
+        qdisc_reset(*old);
+        sch_tree_unlock(sch);
+        return 0;
+}
+
+static struct Qdisc *sfb_leaf(struct Qdisc *sch, unsigned long arg)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+
+        return q->qdisc;
+}
+
+static unsigned long sfb_get(struct Qdisc *sch, u32 classid)
+{
+        return 1;
+}
+
+static void sfb_put(struct Qdisc *sch, unsigned long arg)
+{
+}
+
+static int sfb_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
+                            struct nlattr **tca, unsigned long *arg)
+{
+        return -ENOSYS;
+}
+
+static int sfb_delete(struct Qdisc *sch, unsigned long cl)
+{
+        return -ENOSYS;
+}
+
+static void sfb_walk(struct Qdisc *sch, struct qdisc_walker *walker)
+{
+        if (!walker->stop) {
+                if (walker->count >= walker->skip)
+                        if (walker->fn(sch, 1, walker) < 0) {
+                                walker->stop = 1;
+                                return;
+                        }
+                walker->count++;
+        }
+}
+
+static struct tcf_proto **sfb_find_tcf(struct Qdisc *sch, unsigned long cl)
+{
+        struct sfb_sched_data *q = qdisc_priv(sch);
+
+        if (cl)
+                return NULL;
+        return &q->filter_list;
+}
+
+static unsigned long sfb_bind(struct Qdisc *sch, unsigned long parent,
+                              u32 classid)
+{
+        return 0;
+}
+
+
+static const struct Qdisc_class_ops sfb_class_ops = {
+        .graft          =       sfb_graft,
+        .leaf           =       sfb_leaf,
+        .get            =       sfb_get,
+        .put            =       sfb_put,
+        .change         =       sfb_change_class,
+        .delete         =       sfb_delete,
+        .walk           =       sfb_walk,
+        .tcf_chain      =       sfb_find_tcf,
+        .bind_tcf       =       sfb_bind,
+        .unbind_tcf     =       sfb_put,
+        .dump           =       sfb_dump_class,
+};
+
+static struct Qdisc_ops sfb_qdisc_ops __read_mostly = {
+        .id             =       "sfb",
+        .priv_size      =       sizeof(struct sfb_sched_data),
+        .cl_ops         =       &sfb_class_ops,
+        .enqueue        =       sfb_enqueue,
+        .dequeue        =       sfb_dequeue,
+        .peek           =       sfb_peek,
+        .init           =       sfb_init,
+        .reset          =       sfb_reset,
+        .destroy        =       sfb_destroy,
+        .change         =       sfb_change,
+        .dump           =       sfb_dump,
+        .dump_stats     =       sfb_dump_stats,
+        .owner          =       THIS_MODULE,
+};
+
+static int __init sfb_module_init(void)
+{
+        return register_qdisc(&sfb_qdisc_ops);
+}
+
+static void __exit sfb_module_exit(void)
+{
+        unregister_qdisc(&sfb_qdisc_ops);
+}
+
+module_init(sfb_module_init)
+module_exit(sfb_module_exit)
+
+MODULE_DESCRIPTION("Stochastic Fair Blue queue discipline");
+MODULE_AUTHOR("Juliusz Chroboczek");
+MODULE_AUTHOR("Eric Dumazet");
+MODULE_LICENSE("GPL");