sched: CHOKe flow scheduler
CHOKe ("CHOose and Kill" or "CHOose and Keep") is an alternative
packet scheduler based on the Random Exponential Drop (RED) algorithm.
The core idea is:
For every packet arrival:
Calculate Qave
if (Qave < minth)
Queue the new packet
else
Select randomly a packet from the queue
if (both packets from same flow)
then Drop both the packets
else if (Qave > maxth)
Drop packet
else
Admit packet with proability p (same as RED)
See also:
Rong Pan, Balaji Prabhakar, Konstantinos Psounis, "CHOKe: a stateless active
queue management scheme for approximating fair bandwidth allocation",
Proceeding of INFOCOM'2000, March 2000.
Help from:
Eric Dumazet <eric.dumazet@gmail.com>
Patrick McHardy <kaber@trash.net>
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
index 776cd93..d4bb6f5 100644
--- a/include/linux/pkt_sched.h
+++ b/include/linux/pkt_sched.h
@@ -247,6 +247,35 @@
__u16 pad1;
};
+/* CHOKe section */
+
+enum {
+ TCA_CHOKE_UNSPEC,
+ TCA_CHOKE_PARMS,
+ TCA_CHOKE_STAB,
+ __TCA_CHOKE_MAX,
+};
+
+#define TCA_CHOKE_MAX (__TCA_CHOKE_MAX - 1)
+
+struct tc_choke_qopt {
+ __u32 limit; /* Hard queue length (packets) */
+ __u32 qth_min; /* Min average threshold (packets) */
+ __u32 qth_max; /* Max average threshold (packets) */
+ unsigned char Wlog; /* log(W) */
+ unsigned char Plog; /* log(P_max/(qth_max-qth_min)) */
+ unsigned char Scell_log; /* cell size for idle damping */
+ unsigned char flags; /* see RED flags */
+};
+
+struct tc_choke_xstats {
+ __u32 early; /* Early drops */
+ __u32 pdrop; /* Drops due to queue limits */
+ __u32 other; /* Drops due to drop() calls */
+ __u32 marked; /* Marked packets */
+ __u32 matched; /* Drops due to flow match */
+};
+
/* HTB section */
#define TC_HTB_NUMPRIO 8
#define TC_HTB_MAXDEPTH 8
diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index e318f45..8c19b6e 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -217,6 +217,17 @@
If unsure, say N.
+config NET_SCH_CHOKE
+ tristate "CHOose and Keep responsive flow scheduler (CHOKE)"
+ help
+ Say Y here if you want to use the CHOKe packet scheduler (CHOose
+ and Keep for responsive flows, CHOose and Kill for unresponsive
+ flows). This is a variation of RED which trys to penalize flows
+ that monopolize the queue.
+
+ To compile this code as a module, choose M here: the
+ module will be called sch_choke.
+
config NET_SCH_INGRESS
tristate "Ingress Qdisc"
depends on NET_CLS_ACT
diff --git a/net/sched/Makefile b/net/sched/Makefile
index 26ce681..06c6cdf 100644
--- a/net/sched/Makefile
+++ b/net/sched/Makefile
@@ -33,6 +33,8 @@
obj-$(CONFIG_NET_SCH_NETEM) += sch_netem.o
obj-$(CONFIG_NET_SCH_DRR) += sch_drr.o
obj-$(CONFIG_NET_SCH_MQPRIO) += sch_mqprio.o
+obj-$(CONFIG_NET_SCH_CHOKE) += sch_choke.o
+
obj-$(CONFIG_NET_CLS_U32) += cls_u32.o
obj-$(CONFIG_NET_CLS_ROUTE4) += cls_route.o
obj-$(CONFIG_NET_CLS_FW) += cls_fw.o
diff --git a/net/sched/sch_choke.c b/net/sched/sch_choke.c
new file mode 100644
index 0000000..a1cec18
--- /dev/null
+++ b/net/sched/sch_choke.c
@@ -0,0 +1,676 @@
+/*
+ * net/sched/sch_choke.c CHOKE scheduler
+ *
+ * Copyright (c) 2011 Stephen Hemminger <shemminger@vyatta.com>
+ * 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.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+#include <linux/reciprocal_div.h>
+#include <net/pkt_sched.h>
+#include <net/inet_ecn.h>
+#include <net/red.h>
+#include <linux/ip.h>
+#include <net/ip.h>
+#include <linux/ipv6.h>
+#include <net/ipv6.h>
+
+/*
+ CHOKe stateless AQM for fair bandwidth allocation
+ =================================================
+
+ CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for
+ unresponsive flows) is a variant of RED that penalizes misbehaving flows but
+ maintains no flow state. The difference from RED is an additional step
+ during the enqueuing process. If average queue size is over the
+ low threshold (qmin), a packet is chosen at random from the queue.
+ If both the new and chosen packet are from the same flow, both
+ are dropped. Unlike RED, CHOKe is not really a "classful" qdisc because it
+ needs to access packets in queue randomly. It has a minimal class
+ interface to allow overriding the builtin flow classifier with
+ filters.
+
+ Source:
+ R. Pan, B. Prabhakar, and K. Psounis, "CHOKe, A Stateless
+ Active Queue Management Scheme for Approximating Fair Bandwidth Allocation",
+ IEEE INFOCOM, 2000.
+
+ A. Tang, J. Wang, S. Low, "Understanding CHOKe: Throughput and Spatial
+ Characteristics", IEEE/ACM Transactions on Networking, 2004
+
+ */
+
+/* Upper bound on size of sk_buff table (packets) */
+#define CHOKE_MAX_QUEUE (128*1024 - 1)
+
+struct choke_sched_data {
+/* Parameters */
+ u32 limit;
+ unsigned char flags;
+
+ struct red_parms parms;
+
+/* Variables */
+ struct tcf_proto *filter_list;
+ struct {
+ u32 prob_drop; /* Early probability drops */
+ u32 prob_mark; /* Early probability marks */
+ u32 forced_drop; /* Forced drops, qavg > max_thresh */
+ u32 forced_mark; /* Forced marks, qavg > max_thresh */
+ u32 pdrop; /* Drops due to queue limits */
+ u32 other; /* Drops due to drop() calls */
+ u32 matched; /* Drops to flow match */
+ } stats;
+
+ unsigned int head;
+ unsigned int tail;
+
+ unsigned int tab_mask; /* size - 1 */
+
+ struct sk_buff **tab;
+};
+
+/* deliver a random number between 0 and N - 1 */
+static u32 random_N(unsigned int N)
+{
+ return reciprocal_divide(random32(), N);
+}
+
+/* number of elements in queue including holes */
+static unsigned int choke_len(const struct choke_sched_data *q)
+{
+ return (q->tail - q->head) & q->tab_mask;
+}
+
+/* Is ECN parameter configured */
+static int use_ecn(const struct choke_sched_data *q)
+{
+ return q->flags & TC_RED_ECN;
+}
+
+/* Should packets over max just be dropped (versus marked) */
+static int use_harddrop(const struct choke_sched_data *q)
+{
+ return q->flags & TC_RED_HARDDROP;
+}
+
+/* Move head pointer forward to skip over holes */
+static void choke_zap_head_holes(struct choke_sched_data *q)
+{
+ do {
+ q->head = (q->head + 1) & q->tab_mask;
+ if (q->head == q->tail)
+ break;
+ } while (q->tab[q->head] == NULL);
+}
+
+/* Move tail pointer backwards to reuse holes */
+static void choke_zap_tail_holes(struct choke_sched_data *q)
+{
+ do {
+ q->tail = (q->tail - 1) & q->tab_mask;
+ if (q->head == q->tail)
+ break;
+ } while (q->tab[q->tail] == NULL);
+}
+
+/* Drop packet from queue array by creating a "hole" */
+static void choke_drop_by_idx(struct Qdisc *sch, unsigned int idx)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+ struct sk_buff *skb = q->tab[idx];
+
+ q->tab[idx] = NULL;
+
+ if (idx == q->head)
+ choke_zap_head_holes(q);
+ if (idx == q->tail)
+ choke_zap_tail_holes(q);
+
+ sch->qstats.backlog -= qdisc_pkt_len(skb);
+ qdisc_drop(skb, sch);
+ qdisc_tree_decrease_qlen(sch, 1);
+ --sch->q.qlen;
+}
+
+/*
+ * Compare flow of two packets
+ * Returns true only if source and destination address and port match.
+ * false for special cases
+ */
+static bool choke_match_flow(struct sk_buff *skb1,
+ struct sk_buff *skb2)
+{
+ int off1, off2, poff;
+ const u32 *ports1, *ports2;
+ u8 ip_proto;
+ __u32 hash1;
+
+ if (skb1->protocol != skb2->protocol)
+ return false;
+
+ /* Use hash value as quick check
+ * Assumes that __skb_get_rxhash makes IP header and ports linear
+ */
+ hash1 = skb_get_rxhash(skb1);
+ if (!hash1 || hash1 != skb_get_rxhash(skb2))
+ return false;
+
+ /* Probably match, but be sure to avoid hash collisions */
+ off1 = skb_network_offset(skb1);
+ off2 = skb_network_offset(skb2);
+
+ switch (skb1->protocol) {
+ case __constant_htons(ETH_P_IP): {
+ const struct iphdr *ip1, *ip2;
+
+ ip1 = (const struct iphdr *) (skb1->data + off1);
+ ip2 = (const struct iphdr *) (skb2->data + off2);
+
+ ip_proto = ip1->protocol;
+ if (ip_proto != ip2->protocol ||
+ ip1->saddr != ip2->saddr || ip1->daddr != ip2->daddr)
+ return false;
+
+ if ((ip1->frag_off | ip2->frag_off) & htons(IP_MF | IP_OFFSET))
+ ip_proto = 0;
+ off1 += ip1->ihl * 4;
+ off2 += ip2->ihl * 4;
+ break;
+ }
+
+ case __constant_htons(ETH_P_IPV6): {
+ const struct ipv6hdr *ip1, *ip2;
+
+ ip1 = (const struct ipv6hdr *) (skb1->data + off1);
+ ip2 = (const struct ipv6hdr *) (skb2->data + off2);
+
+ ip_proto = ip1->nexthdr;
+ if (ip_proto != ip2->nexthdr ||
+ ipv6_addr_cmp(&ip1->saddr, &ip2->saddr) ||
+ ipv6_addr_cmp(&ip1->daddr, &ip2->daddr))
+ return false;
+ off1 += 40;
+ off2 += 40;
+ }
+
+ default: /* Maybe compare MAC header here? */
+ return false;
+ }
+
+ poff = proto_ports_offset(ip_proto);
+ if (poff < 0)
+ return true;
+
+ off1 += poff;
+ off2 += poff;
+
+ ports1 = (__force u32 *)(skb1->data + off1);
+ ports2 = (__force u32 *)(skb2->data + off2);
+ return *ports1 == *ports2;
+}
+
+static inline void choke_set_classid(struct sk_buff *skb, u16 classid)
+{
+ *(unsigned int *)(qdisc_skb_cb(skb)->data) = classid;
+}
+
+static u16 choke_get_classid(const struct sk_buff *skb)
+{
+ return *(unsigned int *)(qdisc_skb_cb(skb)->data);
+}
+
+/*
+ * Classify flow using either:
+ * 1. pre-existing classification result in skb
+ * 2. fast internal classification
+ * 3. use TC filter based classification
+ */
+static bool choke_classify(struct sk_buff *skb,
+ struct Qdisc *sch, int *qerr)
+
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+ 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
+ choke_set_classid(skb, TC_H_MIN(res.classid));
+ return true;
+ }
+
+ return false;
+}
+
+/*
+ * Select a packet at random from queue
+ * HACK: since queue can have holes from previous deletion; retry several
+ * times to find a random skb but then just give up and return the head
+ * Will return NULL if queue is empty (q->head == q->tail)
+ */
+static struct sk_buff *choke_peek_random(const struct choke_sched_data *q,
+ unsigned int *pidx)
+{
+ struct sk_buff *skb;
+ int retrys = 3;
+
+ do {
+ *pidx = (q->head + random_N(choke_len(q))) & q->tab_mask;
+ skb = q->tab[*pidx];
+ if (skb)
+ return skb;
+ } while (--retrys > 0);
+
+ return q->tab[*pidx = q->head];
+}
+
+/*
+ * Compare new packet with random packet in queue
+ * returns true if matched and sets *pidx
+ */
+static bool choke_match_random(const struct choke_sched_data *q,
+ struct sk_buff *nskb,
+ unsigned int *pidx)
+{
+ struct sk_buff *oskb;
+
+ if (q->head == q->tail)
+ return false;
+
+ oskb = choke_peek_random(q, pidx);
+ if (q->filter_list)
+ return choke_get_classid(nskb) == choke_get_classid(oskb);
+
+ return choke_match_flow(oskb, nskb);
+}
+
+static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+ struct red_parms *p = &q->parms;
+ int ret = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
+
+ if (q->filter_list) {
+ /* If using external classifiers, get result and record it. */
+ if (!choke_classify(skb, sch, &ret))
+ goto other_drop; /* Packet was eaten by filter */
+ }
+
+ /* Compute average queue usage (see RED) */
+ p->qavg = red_calc_qavg(p, sch->q.qlen);
+ if (red_is_idling(p))
+ red_end_of_idle_period(p);
+
+ /* Is queue small? */
+ if (p->qavg <= p->qth_min)
+ p->qcount = -1;
+ else {
+ unsigned int idx;
+
+ /* Draw a packet at random from queue and compare flow */
+ if (choke_match_random(q, skb, &idx)) {
+ q->stats.matched++;
+ choke_drop_by_idx(sch, idx);
+ goto congestion_drop;
+ }
+
+ /* Queue is large, always mark/drop */
+ if (p->qavg > p->qth_max) {
+ p->qcount = -1;
+
+ sch->qstats.overlimits++;
+ if (use_harddrop(q) || !use_ecn(q) ||
+ !INET_ECN_set_ce(skb)) {
+ q->stats.forced_drop++;
+ goto congestion_drop;
+ }
+
+ q->stats.forced_mark++;
+ } else if (++p->qcount) {
+ if (red_mark_probability(p, p->qavg)) {
+ p->qcount = 0;
+ p->qR = red_random(p);
+
+ sch->qstats.overlimits++;
+ if (!use_ecn(q) || !INET_ECN_set_ce(skb)) {
+ q->stats.prob_drop++;
+ goto congestion_drop;
+ }
+
+ q->stats.prob_mark++;
+ }
+ } else
+ p->qR = red_random(p);
+ }
+
+ /* Admit new packet */
+ if (sch->q.qlen < q->limit) {
+ q->tab[q->tail] = skb;
+ q->tail = (q->tail + 1) & q->tab_mask;
+ ++sch->q.qlen;
+ sch->qstats.backlog += qdisc_pkt_len(skb);
+ return NET_XMIT_SUCCESS;
+ }
+
+ q->stats.pdrop++;
+ sch->qstats.drops++;
+ kfree_skb(skb);
+ return NET_XMIT_DROP;
+
+ congestion_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 *choke_dequeue(struct Qdisc *sch)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+ struct sk_buff *skb;
+
+ if (q->head == q->tail) {
+ if (!red_is_idling(&q->parms))
+ red_start_of_idle_period(&q->parms);
+ return NULL;
+ }
+
+ skb = q->tab[q->head];
+ q->tab[q->head] = NULL;
+ choke_zap_head_holes(q);
+ --sch->q.qlen;
+ sch->qstats.backlog -= qdisc_pkt_len(skb);
+ qdisc_bstats_update(sch, skb);
+
+ return skb;
+}
+
+static unsigned int choke_drop(struct Qdisc *sch)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+ unsigned int len;
+
+ len = qdisc_queue_drop(sch);
+ if (len > 0)
+ q->stats.other++;
+ else {
+ if (!red_is_idling(&q->parms))
+ red_start_of_idle_period(&q->parms);
+ }
+
+ return len;
+}
+
+static void choke_reset(struct Qdisc *sch)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+
+ red_restart(&q->parms);
+}
+
+static const struct nla_policy choke_policy[TCA_CHOKE_MAX + 1] = {
+ [TCA_CHOKE_PARMS] = { .len = sizeof(struct tc_red_qopt) },
+ [TCA_CHOKE_STAB] = { .len = RED_STAB_SIZE },
+};
+
+
+static void choke_free(void *addr)
+{
+ if (addr) {
+ if (is_vmalloc_addr(addr))
+ vfree(addr);
+ else
+ kfree(addr);
+ }
+}
+
+static int choke_change(struct Qdisc *sch, struct nlattr *opt)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+ struct nlattr *tb[TCA_CHOKE_MAX + 1];
+ const struct tc_red_qopt *ctl;
+ int err;
+ struct sk_buff **old = NULL;
+ unsigned int mask;
+
+ if (opt == NULL)
+ return -EINVAL;
+
+ err = nla_parse_nested(tb, TCA_CHOKE_MAX, opt, choke_policy);
+ if (err < 0)
+ return err;
+
+ if (tb[TCA_CHOKE_PARMS] == NULL ||
+ tb[TCA_CHOKE_STAB] == NULL)
+ return -EINVAL;
+
+ ctl = nla_data(tb[TCA_CHOKE_PARMS]);
+
+ if (ctl->limit > CHOKE_MAX_QUEUE)
+ return -EINVAL;
+
+ mask = roundup_pow_of_two(ctl->limit + 1) - 1;
+ if (mask != q->tab_mask) {
+ struct sk_buff **ntab;
+
+ ntab = kcalloc(mask + 1, sizeof(struct sk_buff *), GFP_KERNEL);
+ if (!ntab)
+ ntab = vzalloc((mask + 1) * sizeof(struct sk_buff *));
+ if (!ntab)
+ return -ENOMEM;
+
+ sch_tree_lock(sch);
+ old = q->tab;
+ if (old) {
+ unsigned int oqlen = sch->q.qlen, tail = 0;
+
+ while (q->head != q->tail) {
+ struct sk_buff *skb = q->tab[q->head];
+
+ q->head = (q->head + 1) & q->tab_mask;
+ if (!skb)
+ continue;
+ if (tail < mask) {
+ ntab[tail++] = skb;
+ continue;
+ }
+ sch->qstats.backlog -= qdisc_pkt_len(skb);
+ --sch->q.qlen;
+ qdisc_drop(skb, sch);
+ }
+ qdisc_tree_decrease_qlen(sch, oqlen - sch->q.qlen);
+ q->head = 0;
+ q->tail = tail;
+ }
+
+ q->tab_mask = mask;
+ q->tab = ntab;
+ } else
+ sch_tree_lock(sch);
+
+ q->flags = ctl->flags;
+ q->limit = ctl->limit;
+
+ red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
+ ctl->Plog, ctl->Scell_log,
+ nla_data(tb[TCA_CHOKE_STAB]));
+
+ if (q->head == q->tail)
+ red_end_of_idle_period(&q->parms);
+
+ sch_tree_unlock(sch);
+ choke_free(old);
+ return 0;
+}
+
+static int choke_init(struct Qdisc *sch, struct nlattr *opt)
+{
+ return choke_change(sch, opt);
+}
+
+static int choke_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+ struct nlattr *opts = NULL;
+ struct tc_red_qopt opt = {
+ .limit = q->limit,
+ .flags = q->flags,
+ .qth_min = q->parms.qth_min >> q->parms.Wlog,
+ .qth_max = q->parms.qth_max >> q->parms.Wlog,
+ .Wlog = q->parms.Wlog,
+ .Plog = q->parms.Plog,
+ .Scell_log = q->parms.Scell_log,
+ };
+
+ opts = nla_nest_start(skb, TCA_OPTIONS);
+ if (opts == NULL)
+ goto nla_put_failure;
+
+ NLA_PUT(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt);
+ return nla_nest_end(skb, opts);
+
+nla_put_failure:
+ nla_nest_cancel(skb, opts);
+ return -EMSGSIZE;
+}
+
+static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+ struct tc_choke_xstats st = {
+ .early = q->stats.prob_drop + q->stats.forced_drop,
+ .marked = q->stats.prob_mark + q->stats.forced_mark,
+ .pdrop = q->stats.pdrop,
+ .other = q->stats.other,
+ .matched = q->stats.matched,
+ };
+
+ return gnet_stats_copy_app(d, &st, sizeof(st));
+}
+
+static void choke_destroy(struct Qdisc *sch)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+
+ tcf_destroy_chain(&q->filter_list);
+ choke_free(q->tab);
+}
+
+static struct Qdisc *choke_leaf(struct Qdisc *sch, unsigned long arg)
+{
+ return NULL;
+}
+
+static unsigned long choke_get(struct Qdisc *sch, u32 classid)
+{
+ return 0;
+}
+
+static void choke_put(struct Qdisc *q, unsigned long cl)
+{
+}
+
+static unsigned long choke_bind(struct Qdisc *sch, unsigned long parent,
+ u32 classid)
+{
+ return 0;
+}
+
+static struct tcf_proto **choke_find_tcf(struct Qdisc *sch, unsigned long cl)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+
+ if (cl)
+ return NULL;
+ return &q->filter_list;
+}
+
+static int choke_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 void choke_walk(struct Qdisc *sch, struct qdisc_walker *arg)
+{
+ if (!arg->stop) {
+ if (arg->fn(sch, 1, arg) < 0) {
+ arg->stop = 1;
+ return;
+ }
+ arg->count++;
+ }
+}
+
+static const struct Qdisc_class_ops choke_class_ops = {
+ .leaf = choke_leaf,
+ .get = choke_get,
+ .put = choke_put,
+ .tcf_chain = choke_find_tcf,
+ .bind_tcf = choke_bind,
+ .unbind_tcf = choke_put,
+ .dump = choke_dump_class,
+ .walk = choke_walk,
+};
+
+static struct sk_buff *choke_peek_head(struct Qdisc *sch)
+{
+ struct choke_sched_data *q = qdisc_priv(sch);
+
+ return (q->head != q->tail) ? q->tab[q->head] : NULL;
+}
+
+static struct Qdisc_ops choke_qdisc_ops __read_mostly = {
+ .id = "choke",
+ .priv_size = sizeof(struct choke_sched_data),
+
+ .enqueue = choke_enqueue,
+ .dequeue = choke_dequeue,
+ .peek = choke_peek_head,
+ .drop = choke_drop,
+ .init = choke_init,
+ .destroy = choke_destroy,
+ .reset = choke_reset,
+ .change = choke_change,
+ .dump = choke_dump,
+ .dump_stats = choke_dump_stats,
+ .owner = THIS_MODULE,
+};
+
+static int __init choke_module_init(void)
+{
+ return register_qdisc(&choke_qdisc_ops);
+}
+
+static void __exit choke_module_exit(void)
+{
+ unregister_qdisc(&choke_qdisc_ops);
+}
+
+module_init(choke_module_init)
+module_exit(choke_module_exit)
+
+MODULE_LICENSE("GPL");