sch_fq.c

/*
 * net/sched/sch_fq.c Fair Queue Packet Scheduler (per flow pacing)
 *
 *  Copyright (C) 2013 Eric Dumazet <edumazet@google.com>
 *
 *	This program is free software; you can redistribute it and/or
 *	modify it under the terms of the GNU General Public License
 *	as published by the Free Software Foundation; either version
 *	2 of the License, or (at your option) any later version.
 *
 *  Meant to be mostly used for localy generated traffic :
 *  Fast classification depends on skb->sk being set before reaching us.
 *  If not, (router workload), we use rxhash as fallback, with 32 bits wide hash.
 *  All packets belonging to a socket are considered as a 'flow'.
 *
 *  Flows are dynamically allocated and stored in a hash table of RB trees
 *  They are also part of one Round Robin 'queues' (new or old flows)
 *
 *  Burst avoidance (aka pacing) capability :
 *
 *  Transport (eg TCP) can set in sk->sk_pacing_rate a rate, enqueue a
 *  bunch of packets, and this packet scheduler adds delay between
 *  packets to respect rate limitation.
 *
 *  enqueue() :
 *   - lookup one RB tree (out of 1024 or more) to find the flow.
 *     If non existent flow, create it, add it to the tree.
 *     Add skb to the per flow list of skb (fifo).
 *   - Use a special fifo for high prio packets
 *
 *  dequeue() : serves flows in Round Robin
 *  Note : When a flow becomes empty, we do not immediately remove it from
 *  rb trees, for performance reasons (its expected to send additional packets,
 *  or SLAB cache will reuse socket for another flow)
 */

#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/slab.h>
#include <linux/rbtree.h>
#include <linux/hash.h>
#include <linux/prefetch.h>
#include <linux/vmalloc.h>
#include <net/netlink.h>
#include <net/pkt_sched.h>
#include <net/sock.h>
#include <net/tcp_states.h>

/*
 * Per flow structure, dynamically allocated
 */
struct fq_flow {
	struct sk_buff	*head;		/* list of skbs for this flow : first skb */
	union {
		struct sk_buff *tail;	/* last skb in the list */
		unsigned long  age;	/* jiffies when flow was emptied, for gc */
	};
	struct rb_node	fq_node; 	/* anchor in fq_root[] trees */
	struct sock	*sk;
	int		qlen;		/* number of packets in flow queue */
	int		credit;
	u32		socket_hash;	/* sk_hash */
	struct fq_flow *next;		/* next pointer in RR lists, or &detached */

	struct rb_node  rate_node;	/* anchor in q->delayed tree */
	u64		time_next_packet;
};

struct fq_flow_head {
	struct fq_flow *first;
	struct fq_flow *last;
};

struct fq_sched_data {
	struct fq_flow_head new_flows;

	struct fq_flow_head old_flows;

	struct rb_root	delayed;	/* for rate limited flows */
	u64		time_next_delayed_flow;

	struct fq_flow	internal;	/* for non classified or high prio packets */
	u32		quantum;
	u32		initial_quantum;
	u32		flow_refill_delay;
	u32		flow_max_rate;	/* optional max rate per flow */
	u32		flow_plimit;	/* max packets per flow */
	struct rb_root	*fq_root;
	u8		rate_enable;
	u8		fq_trees_log;

	u32		flows;
	u32		inactive_flows;
	u32		throttled_flows;

	u64		stat_gc_flows;
	u64		stat_internal_packets;
	u64		stat_tcp_retrans;
	u64		stat_throttled;
	u64		stat_flows_plimit;
	u64		stat_pkts_too_long;
	u64		stat_allocation_errors;
	struct qdisc_watchdog watchdog;
};

/* special value to mark a detached flow (not on old/new list) */
static struct fq_flow detached, throttled;

static void fq_flow_set_detached(struct fq_flow *f)
{
	f->next = &detached;
	f->age = jiffies;
}

static bool fq_flow_is_detached(const struct fq_flow *f)
{
	return f->next == &detached;
}

static void fq_flow_set_throttled(struct fq_sched_data *q, struct fq_flow *f)
{
	struct rb_node **p = &q->delayed.rb_node, *parent = NULL;

	while (*p) {
		struct fq_flow *aux;

		parent = *p;
		aux = container_of(parent, struct fq_flow, rate_node);
		if (f->time_next_packet >= aux->time_next_packet)
			p = &parent->rb_right;
		else
			p = &parent->rb_left;
	}
	rb_link_node(&f->rate_node, parent, p);
	rb_insert_color(&f->rate_node, &q->delayed);
	q->throttled_flows++;
	q->stat_throttled++;

	f->next = &throttled;
	if (q->time_next_delayed_flow > f->time_next_packet)
		q->time_next_delayed_flow = f->time_next_packet;
}


static struct kmem_cache *fq_flow_cachep __read_mostly;

static void fq_flow_add_tail(struct fq_flow_head *head, struct fq_flow *flow)
{
	if (head->first)
		head->last->next = flow;
	else
		head->first = flow;
	head->last = flow;
	flow->next = NULL;
}

/* limit number of collected flows per round */
#define FQ_GC_MAX 8
#define FQ_GC_AGE (3*HZ)

static bool fq_gc_candidate(const struct fq_flow *f)
{
	return fq_flow_is_detached(f) &&
	       time_after(jiffies, f->age + FQ_GC_AGE);
}

static void fq_gc(struct fq_sched_data *q,
		  struct rb_root *root,
		  struct sock *sk)
{
	struct fq_flow *f, *tofree[FQ_GC_MAX];
	struct rb_node **p, *parent;
	int fcnt = 0;

	p = &root->rb_node;
	parent = NULL;
	while (*p) {
		parent = *p;

		f = container_of(parent, struct fq_flow, fq_node);
		if (f->sk == sk)
			break;

		if (fq_gc_candidate(f)) {
			tofree[fcnt++] = f;
			if (fcnt == FQ_GC_MAX)
				break;
		}

		if (f->sk > sk)
			p = &parent->rb_right;
		else
			p = &parent->rb_left;
	}

	q->flows -= fcnt;
	q->inactive_flows -= fcnt;
	q->stat_gc_flows += fcnt;
	while (fcnt) {
		struct fq_flow *f = tofree[--fcnt];

		rb_erase(&f->fq_node, root);
		kmem_cache_free(fq_flow_cachep, f);
	}
}

static struct fq_flow *fq_classify(struct sk_buff *skb, struct fq_sched_data *q)
{
	struct rb_node **p, *parent;
	struct sock *sk = skb->sk;
	struct rb_root *root;
	struct fq_flow *f;

	/* warning: no starvation prevention... */
	if (unlikely((skb->priority & TC_PRIO_MAX) == TC_PRIO_CONTROL))
		return &q->internal;

	if (unlikely(!sk)) {
		/* By forcing low order bit to 1, we make sure to not
		 * collide with a local flow (socket pointers are word aligned)
		 */
		sk = (struct sock *)(skb_get_hash(skb) | 1L);
	}

	root = &q->fq_root[hash_32((u32)(long)sk, q->fq_trees_log)];

	if (q->flows >= (2U << q->fq_trees_log) &&
	    q->inactive_flows > q->flows/2)
		fq_gc(q, root, sk);

	p = &root->rb_node;
	parent = NULL;
	while (*p) {
		parent = *p;

		f = container_of(parent, struct fq_flow, fq_node);
		if (f->sk == sk) {
			/* socket might have been reallocated, so check
			 * if its sk_hash is the same.
			 * It not, we need to refill credit with
			 * initial quantum
			 */
			if (unlikely(skb->sk &&
				     f->socket_hash != sk->sk_hash)) {
				f->credit = q->initial_quantum;
				f->socket_hash = sk->sk_hash;
				f->time_next_packet = 0ULL;
			}
			return f;
		}
		if (f->sk > sk)
			p = &parent->rb_right;
		else
			p = &parent->rb_left;
	}

	f = kmem_cache_zalloc(fq_flow_cachep, GFP_ATOMIC | __GFP_NOWARN);
	if (unlikely(!f)) {
		q->stat_allocation_errors++;
		return &q->internal;
	}
	fq_flow_set_detached(f);
	f->sk = sk;
	if (skb->sk)
		f->socket_hash = sk->sk_hash;
	f->credit = q->initial_quantum;

	rb_link_node(&f->fq_node, parent, p);
	rb_insert_color(&f->fq_node, root);

	q->flows++;
	q->inactive_flows++;
	return f;
}


/* remove one skb from head of flow queue */
static struct sk_buff *fq_dequeue_head(struct Qdisc *sch, struct fq_flow *flow)
{
	struct sk_buff *skb = flow->head;

	if (skb) {
		flow->head = skb->next;
		skb->next = NULL;
		flow->qlen--;
		sch->qstats.backlog -= qdisc_pkt_len(skb);
		sch->q.qlen--;
	}
	return skb;
}

/* We might add in the future detection of retransmits
 * For the time being, just return false
 */
static bool skb_is_retransmit(struct sk_buff *skb)
{
	return false;
}

/* add skb to flow queue
 * flow queue is a linked list, kind of FIFO, except for TCP retransmits
 * We special case tcp retransmits to be transmitted before other packets.
 * We rely on fact that TCP retransmits are unlikely, so we do not waste
 * a separate queue or a pointer.
 * head->  [retrans pkt 1]
 *         [retrans pkt 2]
 *         [ normal pkt 1]
 *         [ normal pkt 2]
 *         [ normal pkt 3]
 * tail->  [ normal pkt 4]
 */
static void flow_queue_add(struct fq_flow *flow, struct sk_buff *skb)
{
	struct sk_buff *prev, *head = flow->head;

	skb->next = NULL;
	if (!head) {
		flow->head = skb;
		flow->tail = skb;
		return;
	}
	if (likely(!skb_is_retransmit(skb))) {
		flow->tail->next = skb;
		flow->tail = skb;
		return;
	}

	/* This skb is a tcp retransmit,
	 * find the last retrans packet in the queue
	 */
	prev = NULL;
	while (skb_is_retransmit(head)) {
		prev = head;
		head = head->next;
		if (!head)
			break;
	}
	if (!prev) { /* no rtx packet in queue, become the new head */
		skb->next = flow->head;
		flow->head = skb;
	} else {
		if (prev == flow->tail)
			flow->tail = skb;
		else
			skb->next = prev->next;
		prev->next = skb;
	}
}

static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
	struct fq_sched_data *q = qdisc_priv(sch);
	struct fq_flow *f;

	if (unlikely(sch->q.qlen >= sch->limit))
		return qdisc_drop(skb, sch);

	f = fq_classify(skb, q);
	if (unlikely(f->qlen >= q->flow_plimit && f != &q->internal)) {
		q->stat_flows_plimit++;
		return qdisc_drop(skb, sch);
	}

	f->qlen++;
	if (skb_is_retransmit(skb))
		q->stat_tcp_retrans++;
	sch->qstats.backlog += qdisc_pkt_len(skb);
	if (fq_flow_is_detached(f)) {
		fq_flow_add_tail(&q->new_flows, f);
		if (time_after(jiffies, f->age + q->flow_refill_delay))
			f->credit = max_t(u32, f->credit, q->quantum);
		q->inactive_flows--;
		qdisc_unthrottled(sch);
	}

	/* Note: this overwrites f->age */
	flow_queue_add(f, skb);

	if (unlikely(f == &q->internal)) {
		q->stat_internal_packets++;
		qdisc_unthrottled(sch);
	}
	sch->q.qlen++;

	return NET_XMIT_SUCCESS;
}

static void fq_check_throttled(struct fq_sched_data *q, u64 now)
{
	struct rb_node *p;

	if (q->time_next_delayed_flow > now)
		return;

	q->time_next_delayed_flow = ~0ULL;
	while ((p = rb_first(&q->delayed)) != NULL) {
		struct fq_flow *f = container_of(p, struct fq_flow, rate_node);

		if (f->time_next_packet > now) {
			q->time_next_delayed_flow = f->time_next_packet;
			break;
		}
		rb_erase(p, &q->delayed);
		q->throttled_flows--;
		fq_flow_add_tail(&q->old_flows, f);
	}
}

static struct sk_buff *fq_dequeue(struct Qdisc *sch)
{
	struct fq_sched_data *q = qdisc_priv(sch);
	u64 now = ktime_to_ns(ktime_get());
	struct fq_flow_head *head;
	struct sk_buff *skb;
	struct fq_flow *f;
	u32 rate;

	skb = fq_dequeue_head(sch, &q->internal);
	if (skb)
		goto out;
	fq_check_throttled(q, now);
begin:
	head = &q->new_flows;
	if (!head->first) {
		head = &q->old_flows;
		if (!head->first) {
			if (q->time_next_delayed_flow != ~0ULL)
				qdisc_watchdog_schedule_ns(&q->watchdog,
							   q->time_next_delayed_flow);
			return NULL;
		}
	}
	f = head->first;

	if (f->credit <= 0) {
		f->credit += q->quantum;
		head->first = f->next;
		fq_flow_add_tail(&q->old_flows, f);
		goto begin;
	}

	if (unlikely(f->head && now < f->time_next_packet)) {
		head->first = f->next;
		fq_flow_set_throttled(q, f);
		goto begin;
	}

	skb = fq_dequeue_head(sch, f);
	if (!skb) {
		head->first = f->next;
		/* force a pass through old_flows to prevent starvation */
		if ((head == &q->new_flows) && q->old_flows.first) {
			fq_flow_add_tail(&q->old_flows, f);
		} else {
			fq_flow_set_detached(f);
			q->inactive_flows++;
		}
		goto begin;
	}
	prefetch(&skb->end);
	f->time_next_packet = now;
	f->credit -= qdisc_pkt_len(skb);

	if (f->credit > 0 || !q->rate_enable)
		goto out;

	rate = q->flow_max_rate;
	if (skb->sk && skb->sk->sk_state != TCP_TIME_WAIT)
		rate = min(skb->sk->sk_pacing_rate, rate);

	if (rate != ~0U) {
		u32 plen = max(qdisc_pkt_len(skb), q->quantum);
		u64 len = (u64)plen * NSEC_PER_SEC;

		if (likely(rate))
			do_div(len, rate);
		/* Since socket rate can change later,
		 * clamp the delay to 125 ms.
		 * TODO: maybe segment the too big skb, as in commit
		 * e43ac79a4bc ("sch_tbf: segment too big GSO packets")
		 */
		if (unlikely(len > 125 * NSEC_PER_MSEC)) {
			len = 125 * NSEC_PER_MSEC;
			q->stat_pkts_too_long++;
		}

		f->time_next_packet = now + len;
	}
out:
	qdisc_bstats_update(sch, skb);
	qdisc_unthrottled(sch);
	return skb;
}

static void fq_reset(struct Qdisc *sch)
{
	struct fq_sched_data *q = qdisc_priv(sch);
	struct rb_root *root;
	struct sk_buff *skb;
	struct rb_node *p;
	struct fq_flow *f;
	unsigned int idx;

	while ((skb = fq_dequeue_head(sch, &q->internal)) != NULL)
		kfree_skb(skb);

	if (!q->fq_root)
		return;

	for (idx = 0; idx < (1U << q->fq_trees_log); idx++) {
		root = &q->fq_root[idx];
		while ((p = rb_first(root)) != NULL) {
			f = container_of(p, struct fq_flow, fq_node);
			rb_erase(p, root);

			while ((skb = fq_dequeue_head(sch, f)) != NULL)
				kfree_skb(skb);

			kmem_cache_free(fq_flow_cachep, f);
		}
	}
	q->new_flows.first	= NULL;
	q->old_flows.first	= NULL;
	q->delayed		= RB_ROOT;
	q->flows		= 0;
	q->inactive_flows	= 0;
	q->throttled_flows	= 0;
}

static void fq_rehash(struct fq_sched_data *q,
		      struct rb_root *old_array, u32 old_log,
		      struct rb_root *new_array, u32 new_log)
{
	struct rb_node *op, **np, *parent;
	struct rb_root *oroot, *nroot;
	struct fq_flow *of, *nf;
	int fcnt = 0;
	u32 idx;

	for (idx = 0; idx < (1U << old_log); idx++) {
		oroot = &old_array[idx];
		while ((op = rb_first(oroot)) != NULL) {
			rb_erase(op, oroot);
			of = container_of(op, struct fq_flow, fq_node);
			if (fq_gc_candidate(of)) {
				fcnt++;
				kmem_cache_free(fq_flow_cachep, of);
				continue;
			}
			nroot = &new_array[hash_32((u32)(long)of->sk, new_log)];

			np = &nroot->rb_node;
			parent = NULL;
			while (*np) {
				parent = *np;

				nf = container_of(parent, struct fq_flow, fq_node);
				BUG_ON(nf->sk == of->sk);

				if (nf->sk > of->sk)
					np = &parent->rb_right;
				else
					np = &parent->rb_left;
			}

			rb_link_node(&of->fq_node, parent, np);
			rb_insert_color(&of->fq_node, nroot);
		}
	}
	q->flows -= fcnt;
	q->inactive_flows -= fcnt;
	q->stat_gc_flows += fcnt;
}

static void *fq_alloc_node(size_t sz, int node)
{
	void *ptr;

	ptr = kmalloc_node(sz, GFP_KERNEL | __GFP_REPEAT | __GFP_NOWARN, node);
	if (!ptr)
		ptr = vmalloc_node(sz, node);
	return ptr;
}

static void fq_free(void *addr)
{
	kvfree(addr);
}

static int fq_resize(struct Qdisc *sch, u32 log)
{
	struct fq_sched_data *q = qdisc_priv(sch);
	struct rb_root *array;
	void *old_fq_root;
	u32 idx;

	if (q->fq_root && log == q->fq_trees_log)
		return 0;

	/* If XPS was setup, we can allocate memory on right NUMA node */
	array = fq_alloc_node(sizeof(struct rb_root) << log,
			      netdev_queue_numa_node_read(sch->dev_queue));
	if (!array)
		return -ENOMEM;

	for (idx = 0; idx < (1U << log); idx++)
		array[idx] = RB_ROOT;

	sch_tree_lock(sch);

	old_fq_root = q->fq_root;
	if (old_fq_root)
		fq_rehash(q, old_fq_root, q->fq_trees_log, array, log);

	q->fq_root = array;
	q->fq_trees_log = log;

	sch_tree_unlock(sch);

	fq_free(old_fq_root);

	return 0;
}

static const struct nla_policy fq_policy[TCA_FQ_MAX + 1] = {
	[TCA_FQ_PLIMIT]			= { .type = NLA_U32 },
	[TCA_FQ_FLOW_PLIMIT]		= { .type = NLA_U32 },
	[TCA_FQ_QUANTUM]		= { .type = NLA_U32 },
	[TCA_FQ_INITIAL_QUANTUM]	= { .type = NLA_U32 },
	[TCA_FQ_RATE_ENABLE]		= { .type = NLA_U32 },
	[TCA_FQ_FLOW_DEFAULT_RATE]	= { .type = NLA_U32 },
	[TCA_FQ_FLOW_MAX_RATE]		= { .type = NLA_U32 },
	[TCA_FQ_BUCKETS_LOG]		= { .type = NLA_U32 },
	[TCA_FQ_FLOW_REFILL_DELAY]	= { .type = NLA_U32 },
};

static int fq_change(struct Qdisc *sch, struct nlattr *opt)
{
	struct fq_sched_data *q = qdisc_priv(sch);
	struct nlattr *tb[TCA_FQ_MAX + 1];
	int err, drop_count = 0;
	u32 fq_log;

	if (!opt)
		return -EINVAL;

	err = nla_parse_nested(tb, TCA_FQ_MAX, opt, fq_policy);
	if (err < 0)
		return err;

	sch_tree_lock(sch);

	fq_log = q->fq_trees_log;

	if (tb[TCA_FQ_BUCKETS_LOG]) {
		u32 nval = nla_get_u32(tb[TCA_FQ_BUCKETS_LOG]);

		if (nval >= 1 && nval <= ilog2(256*1024))
			fq_log = nval;
		else
			err = -EINVAL;
	}
	if (tb[TCA_FQ_PLIMIT])
		sch->limit = nla_get_u32(tb[TCA_FQ_PLIMIT]);

	if (tb[TCA_FQ_FLOW_PLIMIT])
		q->flow_plimit = nla_get_u32(tb[TCA_FQ_FLOW_PLIMIT]);

	if (tb[TCA_FQ_QUANTUM])
		q->quantum = nla_get_u32(tb[TCA_FQ_QUANTUM]);

	if (tb[TCA_FQ_INITIAL_QUANTUM])
		q->initial_quantum = nla_get_u32(tb[TCA_FQ_INITIAL_QUANTUM]);

	if (tb[TCA_FQ_FLOW_DEFAULT_RATE])
		pr_warn_ratelimited("sch_fq: defrate %u ignored.\n",
				    nla_get_u32(tb[TCA_FQ_FLOW_DEFAULT_RATE]));

	if (tb[TCA_FQ_FLOW_MAX_RATE])
		q->flow_max_rate = nla_get_u32(tb[TCA_FQ_FLOW_MAX_RATE]);

	if (tb[TCA_FQ_RATE_ENABLE]) {
		u32 enable = nla_get_u32(tb[TCA_FQ_RATE_ENABLE]);

		if (enable <= 1)
			q->rate_enable = enable;
		else
			err = -EINVAL;
	}

	if (tb[TCA_FQ_FLOW_REFILL_DELAY]) {
		u32 usecs_delay = nla_get_u32(tb[TCA_FQ_FLOW_REFILL_DELAY]) ;

		q->flow_refill_delay = usecs_to_jiffies(usecs_delay);
	}

	if (!err) {
		sch_tree_unlock(sch);
		err = fq_resize(sch, fq_log);
		sch_tree_lock(sch);
	}
	while (sch->q.qlen > sch->limit) {
		struct sk_buff *skb = fq_dequeue(sch);

		if (!skb)
			break;
		kfree_skb(skb);
		drop_count++;
	}
	qdisc_tree_decrease_qlen(sch, drop_count);

	sch_tree_unlock(sch);
	return err;
}

static void fq_destroy(struct Qdisc *sch)
{
	struct fq_sched_data *q = qdisc_priv(sch);

	fq_reset(sch);
	fq_free(q->fq_root);
	qdisc_watchdog_cancel(&q->watchdog);
}

static int fq_init(struct Qdisc *sch, struct nlattr *opt)
{
	struct fq_sched_data *q = qdisc_priv(sch);
	int err;

	sch->limit		= 10000;
	q->flow_plimit		= 100;
	q->quantum		= 2 * psched_mtu(qdisc_dev(sch));
	q->initial_quantum	= 10 * psched_mtu(qdisc_dev(sch));
	q->flow_refill_delay	= msecs_to_jiffies(40);
	q->flow_max_rate	= ~0U;
	q->rate_enable		= 1;
	q->new_flows.first	= NULL;
	q->old_flows.first	= NULL;
	q->delayed		= RB_ROOT;
	q->fq_root		= NULL;
	q->fq_trees_log		= ilog2(1024);
	qdisc_watchdog_init(&q->watchdog, sch);

	if (opt)
		err = fq_change(sch, opt);
	else
		err = fq_resize(sch, q->fq_trees_log);

	return err;
}

static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
{
	struct fq_sched_data *q = qdisc_priv(sch);
	struct nlattr *opts;

	opts = nla_nest_start(skb, TCA_OPTIONS);
	if (opts == NULL)
		goto nla_put_failure;

	/* TCA_FQ_FLOW_DEFAULT_RATE is not used anymore */

	if (nla_put_u32(skb, TCA_FQ_PLIMIT, sch->limit) ||
	    nla_put_u32(skb, TCA_FQ_FLOW_PLIMIT, q->flow_plimit) ||
	    nla_put_u32(skb, TCA_FQ_QUANTUM, q->quantum) ||
	    nla_put_u32(skb, TCA_FQ_INITIAL_QUANTUM, q->initial_quantum) ||
	    nla_put_u32(skb, TCA_FQ_RATE_ENABLE, q->rate_enable) ||
	    nla_put_u32(skb, TCA_FQ_FLOW_MAX_RATE, q->flow_max_rate) ||
	    nla_put_u32(skb, TCA_FQ_FLOW_REFILL_DELAY,
			jiffies_to_usecs(q->flow_refill_delay)) ||
	    nla_put_u32(skb, TCA_FQ_BUCKETS_LOG, q->fq_trees_log))
		goto nla_put_failure;

	return nla_nest_end(skb, opts);

nla_put_failure:
	return -1;
}

static int fq_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
{
	struct fq_sched_data *q = qdisc_priv(sch);
	u64 now = ktime_to_ns(ktime_get());
	struct tc_fq_qd_stats st = {
		.gc_flows		= q->stat_gc_flows,
		.highprio_packets	= q->stat_internal_packets,
		.tcp_retrans		= q->stat_tcp_retrans,
		.throttled		= q->stat_throttled,
		.flows_plimit		= q->stat_flows_plimit,
		.pkts_too_long		= q->stat_pkts_too_long,
		.allocation_errors	= q->stat_allocation_errors,
		.flows			= q->flows,
		.inactive_flows		= q->inactive_flows,
		.throttled_flows	= q->throttled_flows,
		.time_next_delayed_flow	= q->time_next_delayed_flow - now,
	};

	return gnet_stats_copy_app(d, &st, sizeof(st));
}

static struct Qdisc_ops fq_qdisc_ops __read_mostly = {
	.id		=	"fq",
	.priv_size	=	sizeof(struct fq_sched_data),

	.enqueue	=	fq_enqueue,
	.dequeue	=	fq_dequeue,
	.peek		=	qdisc_peek_dequeued,
	.init		=	fq_init,
	.reset		=	fq_reset,
	.destroy	=	fq_destroy,
	.change		=	fq_change,
	.dump		=	fq_dump,
	.dump_stats	=	fq_dump_stats,
	.owner		=	THIS_MODULE,
};

static int __init fq_module_init(void)
{
	int ret;

	fq_flow_cachep = kmem_cache_create("fq_flow_cache",
					   sizeof(struct fq_flow),
					   0, 0, NULL);
	if (!fq_flow_cachep)
		return -ENOMEM;

	ret = register_qdisc(&fq_qdisc_ops);
	if (ret)
		kmem_cache_destroy(fq_flow_cachep);
	return ret;
}

static void __exit fq_module_exit(void)
{
	unregister_qdisc(&fq_qdisc_ops);
	kmem_cache_destroy(fq_flow_cachep);
}

module_init(fq_module_init)
module_exit(fq_module_exit)
MODULE_AUTHOR("Eric Dumazet");
MODULE_LICENSE("GPL");