sch_qfq.c

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/*
 * net/sched/sch_qfq.c         Quick Fair Queueing Scheduler.
 *
 * Copyright (c) 2009 Fabio Checconi, Luigi Rizzo, and Paolo Valente.
 *
 * 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/init.h>
#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/pkt_sched.h>
#include <net/sch_generic.h>
#include <net/pkt_sched.h>
#include <net/pkt_cls.h>


/*  Quick Fair Queueing
    ===================

    Sources:

    Fabio Checconi, Luigi Rizzo, and Paolo Valente: "QFQ: Efficient
    Packet Scheduling with Tight Bandwidth Distribution Guarantees."

    See also:
    http://retis.sssup.it/~fabio/linux/qfq/
 */

/*

  Virtual time computations.

  S, F and V are all computed in fixed point arithmetic with
  FRAC_BITS decimal bits.

  QFQ_MAX_INDEX is the maximum index allowed for a group. We need
    one bit per index.
  QFQ_MAX_WSHIFT is the maximum power of two supported as a weight.

  The layout of the bits is as below:

                   [ MTU_SHIFT ][      FRAC_BITS    ]
                   [ MAX_INDEX    ][ MIN_SLOT_SHIFT ]
                 ^.__grp->index = 0
                 *.__grp->slot_shift

  where MIN_SLOT_SHIFT is derived by difference from the others.

  The max group index corresponds to Lmax/w_min, where
  Lmax=1<<MTU_SHIFT, w_min = 1 .
  From this, and knowing how many groups (MAX_INDEX) we want,
  we can derive the shift corresponding to each group.

  Because we often need to compute
    F = S + len/w_i  and V = V + len/wsum
  instead of storing w_i store the value
    inv_w = (1<<FRAC_BITS)/w_i
  so we can do F = S + len * inv_w * wsum.
  We use W_TOT in the formulas so we can easily move between
  static and adaptive weight sum.

  The per-scheduler-instance data contain all the data structures
  for the scheduler: bitmaps and bucket lists.

 */

/*
 * Maximum number of consecutive slots occupied by backlogged classes
 * inside a group.
 */
#define QFQ_MAX_SLOTS   32

/*
 * Shifts used for class<->group mapping.  We allow class weights that are
 * in the range [1, 2^MAX_WSHIFT], and we try to map each class i to the
 * group with the smallest index that can support the L_i / r_i configured
 * for the class.
 *
 * grp->index is the index of the group; and grp->slot_shift
 * is the shift for the corresponding (scaled) sigma_i.
 */
#define QFQ_MAX_INDEX       24
#define QFQ_MAX_WSHIFT      12

#define QFQ_MAX_WEIGHT      (1<<QFQ_MAX_WSHIFT)
#define QFQ_MAX_WSUM        (16*QFQ_MAX_WEIGHT)

#define FRAC_BITS       30  /* fixed point arithmetic */
#define ONE_FP          (1UL << FRAC_BITS)
#define IWSUM           (ONE_FP/QFQ_MAX_WSUM)

#define QFQ_MTU_SHIFT       16  /* to support TSO/GSO */
#define QFQ_MIN_SLOT_SHIFT  (FRAC_BITS + QFQ_MTU_SHIFT - QFQ_MAX_INDEX)
#define QFQ_MIN_LMAX        256 /* min possible lmax for a class */

/*
 * Possible group states.  These values are used as indexes for the bitmaps
 * array of struct qfq_queue.
 */
enum qfq_state { ER, IR, EB, IB, QFQ_MAX_STATE };

struct qfq_group;

struct qfq_class {
    struct Qdisc_class_common common;

    unsigned int refcnt;
    unsigned int filter_cnt;

    struct gnet_stats_basic_packed bstats;
    struct gnet_stats_queue qstats;
    struct gnet_stats_rate_est rate_est;
    struct Qdisc *qdisc;

    struct hlist_node next; /* Link for the slot list. */
    u64 S, F;       /* flow timestamps (exact) */

    /* group we belong to. In principle we would need the index,
     * which is log_2(lmax/weight), but we never reference it
     * directly, only the group.
     */
    struct qfq_group *grp;

    /* these are copied from the flowset. */
    u32 inv_w;      /* ONE_FP/weight */
    u32 lmax;       /* Max packet size for this flow. */
};

struct qfq_group {
    u64 S, F;           /* group timestamps (approx). */
    unsigned int slot_shift;    /* Slot shift. */
    unsigned int index;     /* Group index. */
    unsigned int front;     /* Index of the front slot. */
    unsigned long full_slots;   /* non-empty slots */

    /* Array of RR lists of active classes. */
    struct hlist_head slots[QFQ_MAX_SLOTS];
};

struct qfq_sched {
    struct tcf_proto *filter_list;
    struct Qdisc_class_hash clhash;

    u64     V;      /* Precise virtual time. */
    u32     wsum;       /* weight sum */

    unsigned long bitmaps[QFQ_MAX_STATE];       /* Group bitmaps. */
    struct qfq_group groups[QFQ_MAX_INDEX + 1]; /* The groups. */
};

static struct qfq_class *qfq_find_class(struct Qdisc *sch, u32 classid)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct Qdisc_class_common *clc;

    clc = qdisc_class_find(&q->clhash, classid);
    if (clc == NULL)
        return NULL;
    return container_of(clc, struct qfq_class, common);
}

static void qfq_purge_queue(struct qfq_class *cl)
{
    unsigned int len = cl->qdisc->q.qlen;

    qdisc_reset(cl->qdisc);
    qdisc_tree_decrease_qlen(cl->qdisc, len);
}

static const struct nla_policy qfq_policy[TCA_QFQ_MAX + 1] = {
    [TCA_QFQ_WEIGHT] = { .type = NLA_U32 },
    [TCA_QFQ_LMAX] = { .type = NLA_U32 },
};

/*
 * Calculate a flow index, given its weight and maximum packet length.
 * index = log_2(maxlen/weight) but we need to apply the scaling.
 * This is used only once at flow creation.
 */
static int qfq_calc_index(u32 inv_w, unsigned int maxlen)
{
    u64 slot_size = (u64)maxlen * inv_w;
    unsigned long size_map;
    int index = 0;

    size_map = slot_size >> QFQ_MIN_SLOT_SHIFT;
    if (!size_map)
        goto out;

    index = __fls(size_map) + 1;    /* basically a log_2 */
    index -= !(slot_size - (1ULL << (index + QFQ_MIN_SLOT_SHIFT - 1)));

    if (index < 0)
        index = 0;
out:
    pr_debug("qfq calc_index: W = %lu, L = %u, I = %d\n",
         (unsigned long) ONE_FP/inv_w, maxlen, index);

    return index;
}

/* Length of the next packet (0 if the queue is empty). */
static unsigned int qdisc_peek_len(struct Qdisc *sch)
{
    struct sk_buff *skb;

    skb = sch->ops->peek(sch);
    return skb ? qdisc_pkt_len(skb) : 0;
}

static void qfq_deactivate_class(struct qfq_sched *, struct qfq_class *);
static void qfq_activate_class(struct qfq_sched *q, struct qfq_class *cl,
                   unsigned int len);

static void qfq_update_class_params(struct qfq_sched *q, struct qfq_class *cl,
                    u32 lmax, u32 inv_w, int delta_w)
{
    int i;

    /* update qfq-specific data */
    cl->lmax = lmax;
    cl->inv_w = inv_w;
    i = qfq_calc_index(cl->inv_w, cl->lmax);

    cl->grp = &q->groups[i];

    q->wsum += delta_w;
}

static void qfq_update_reactivate_class(struct qfq_sched *q,
                    struct qfq_class *cl,
                    u32 inv_w, u32 lmax, int delta_w)
{
    bool need_reactivation = false;
    int i = qfq_calc_index(inv_w, lmax);

    if (&q->groups[i] != cl->grp && cl->qdisc->q.qlen > 0) {
        /*
         * shift cl->F back, to not charge the
         * class for the not-yet-served head
         * packet
         */
        cl->F = cl->S;
        /* remove class from its slot in the old group */
        qfq_deactivate_class(q, cl);
        need_reactivation = true;
    }

    qfq_update_class_params(q, cl, lmax, inv_w, delta_w);

    if (need_reactivation) /* activate in new group */
        qfq_activate_class(q, cl, qdisc_peek_len(cl->qdisc));
}


static int qfq_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
                struct nlattr **tca, unsigned long *arg)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_class *cl = (struct qfq_class *)*arg;
    struct nlattr *tb[TCA_QFQ_MAX + 1];
    u32 weight, lmax, inv_w;
    int err;
    int delta_w;

    if (tca[TCA_OPTIONS] == NULL) {
        pr_notice("qfq: no options\n");
        return -EINVAL;
    }

    err = nla_parse_nested(tb, TCA_QFQ_MAX, tca[TCA_OPTIONS], qfq_policy);
    if (err < 0)
        return err;

    if (tb[TCA_QFQ_WEIGHT]) {
        weight = nla_get_u32(tb[TCA_QFQ_WEIGHT]);
        if (!weight || weight > (1UL << QFQ_MAX_WSHIFT)) {
            pr_notice("qfq: invalid weight %u\n", weight);
            return -EINVAL;
        }
    } else
        weight = 1;

    inv_w = ONE_FP / weight;
    weight = ONE_FP / inv_w;
    delta_w = weight - (cl ? ONE_FP / cl->inv_w : 0);
    if (q->wsum + delta_w > QFQ_MAX_WSUM) {
        pr_notice("qfq: total weight out of range (%u + %u)\n",
              delta_w, q->wsum);
        return -EINVAL;
    }

    if (tb[TCA_QFQ_LMAX]) {
        lmax = nla_get_u32(tb[TCA_QFQ_LMAX]);
        if (lmax < QFQ_MIN_LMAX || lmax > (1UL << QFQ_MTU_SHIFT)) {
            pr_notice("qfq: invalid max length %u\n", lmax);
            return -EINVAL;
        }
    } else
        lmax = psched_mtu(qdisc_dev(sch));

    if (cl != NULL) {
        if (tca[TCA_RATE]) {
            err = gen_replace_estimator(&cl->bstats, &cl->rate_est,
                            qdisc_root_sleeping_lock(sch),
                            tca[TCA_RATE]);
            if (err)
                return err;
        }

        if (lmax == cl->lmax && inv_w == cl->inv_w)
            return 0; /* nothing to update */

        sch_tree_lock(sch);
        qfq_update_reactivate_class(q, cl, inv_w, lmax, delta_w);
        sch_tree_unlock(sch);

        return 0;
    }

    cl = kzalloc(sizeof(struct qfq_class), GFP_KERNEL);
    if (cl == NULL)
        return -ENOBUFS;

    cl->refcnt = 1;
    cl->common.classid = classid;

    qfq_update_class_params(q, cl, lmax, inv_w, delta_w);

    cl->qdisc = qdisc_create_dflt(sch->dev_queue,
                      &pfifo_qdisc_ops, classid);
    if (cl->qdisc == NULL)
        cl->qdisc = &noop_qdisc;

    if (tca[TCA_RATE]) {
        err = gen_new_estimator(&cl->bstats, &cl->rate_est,
                    qdisc_root_sleeping_lock(sch),
                    tca[TCA_RATE]);
        if (err) {
            qdisc_destroy(cl->qdisc);
            kfree(cl);
            return err;
        }
    }

    sch_tree_lock(sch);
    qdisc_class_hash_insert(&q->clhash, &cl->common);
    sch_tree_unlock(sch);

    qdisc_class_hash_grow(sch, &q->clhash);

    *arg = (unsigned long)cl;
    return 0;
}

static void qfq_destroy_class(struct Qdisc *sch, struct qfq_class *cl)
{
    struct qfq_sched *q = qdisc_priv(sch);

    if (cl->inv_w) {
        q->wsum -= ONE_FP / cl->inv_w;
        cl->inv_w = 0;
    }

    gen_kill_estimator(&cl->bstats, &cl->rate_est);
    qdisc_destroy(cl->qdisc);
    kfree(cl);
}

static int qfq_delete_class(struct Qdisc *sch, unsigned long arg)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_class *cl = (struct qfq_class *)arg;

    if (cl->filter_cnt > 0)
        return -EBUSY;

    sch_tree_lock(sch);

    qfq_purge_queue(cl);
    qdisc_class_hash_remove(&q->clhash, &cl->common);

    BUG_ON(--cl->refcnt == 0);
    /*
     * This shouldn't happen: we "hold" one cops->get() when called
     * from tc_ctl_tclass; the destroy method is done from cops->put().
     */

    sch_tree_unlock(sch);
    return 0;
}

static unsigned long qfq_get_class(struct Qdisc *sch, u32 classid)
{
    struct qfq_class *cl = qfq_find_class(sch, classid);

    if (cl != NULL)
        cl->refcnt++;

    return (unsigned long)cl;
}

static void qfq_put_class(struct Qdisc *sch, unsigned long arg)
{
    struct qfq_class *cl = (struct qfq_class *)arg;

    if (--cl->refcnt == 0)
        qfq_destroy_class(sch, cl);
}

static struct tcf_proto **qfq_tcf_chain(struct Qdisc *sch, unsigned long cl)
{
    struct qfq_sched *q = qdisc_priv(sch);

    if (cl)
        return NULL;

    return &q->filter_list;
}

static unsigned long qfq_bind_tcf(struct Qdisc *sch, unsigned long parent,
                  u32 classid)
{
    struct qfq_class *cl = qfq_find_class(sch, classid);

    if (cl != NULL)
        cl->filter_cnt++;

    return (unsigned long)cl;
}

static void qfq_unbind_tcf(struct Qdisc *sch, unsigned long arg)
{
    struct qfq_class *cl = (struct qfq_class *)arg;

    cl->filter_cnt--;
}

static int qfq_graft_class(struct Qdisc *sch, unsigned long arg,
               struct Qdisc *new, struct Qdisc **old)
{
    struct qfq_class *cl = (struct qfq_class *)arg;

    if (new == NULL) {
        new = qdisc_create_dflt(sch->dev_queue,
                    &pfifo_qdisc_ops, cl->common.classid);
        if (new == NULL)
            new = &noop_qdisc;
    }

    sch_tree_lock(sch);
    qfq_purge_queue(cl);
    *old = cl->qdisc;
    cl->qdisc = new;
    sch_tree_unlock(sch);
    return 0;
}

static struct Qdisc *qfq_class_leaf(struct Qdisc *sch, unsigned long arg)
{
    struct qfq_class *cl = (struct qfq_class *)arg;

    return cl->qdisc;
}

static int qfq_dump_class(struct Qdisc *sch, unsigned long arg,
              struct sk_buff *skb, struct tcmsg *tcm)
{
    struct qfq_class *cl = (struct qfq_class *)arg;
    struct nlattr *nest;

    tcm->tcm_parent = TC_H_ROOT;
    tcm->tcm_handle = cl->common.classid;
    tcm->tcm_info   = cl->qdisc->handle;

    nest = nla_nest_start(skb, TCA_OPTIONS);
    if (nest == NULL)
        goto nla_put_failure;
    if (nla_put_u32(skb, TCA_QFQ_WEIGHT, ONE_FP/cl->inv_w) ||
        nla_put_u32(skb, TCA_QFQ_LMAX, cl->lmax))
        goto nla_put_failure;
    return nla_nest_end(skb, nest);

nla_put_failure:
    nla_nest_cancel(skb, nest);
    return -EMSGSIZE;
}

static int qfq_dump_class_stats(struct Qdisc *sch, unsigned long arg,
                struct gnet_dump *d)
{
    struct qfq_class *cl = (struct qfq_class *)arg;
    struct tc_qfq_stats xstats;

    memset(&xstats, 0, sizeof(xstats));
    cl->qdisc->qstats.qlen = cl->qdisc->q.qlen;

    xstats.weight = ONE_FP/cl->inv_w;
    xstats.lmax = cl->lmax;

    if (gnet_stats_copy_basic(d, &cl->bstats) < 0 ||
        gnet_stats_copy_rate_est(d, &cl->bstats, &cl->rate_est) < 0 ||
        gnet_stats_copy_queue(d, &cl->qdisc->qstats) < 0)
        return -1;

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

static void qfq_walk(struct Qdisc *sch, struct qdisc_walker *arg)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_class *cl;
    struct hlist_node *n;
    unsigned int i;

    if (arg->stop)
        return;

    for (i = 0; i < q->clhash.hashsize; i++) {
        hlist_for_each_entry(cl, n, &q->clhash.hash[i], common.hnode) {
            if (arg->count < arg->skip) {
                arg->count++;
                continue;
            }
            if (arg->fn(sch, (unsigned long)cl, arg) < 0) {
                arg->stop = 1;
                return;
            }
            arg->count++;
        }
    }
}

static struct qfq_class *qfq_classify(struct sk_buff *skb, struct Qdisc *sch,
                      int *qerr)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_class *cl;
    struct tcf_result res;
    int result;

    if (TC_H_MAJ(skb->priority ^ sch->handle) == 0) {
        pr_debug("qfq_classify: found %d\n", skb->priority);
        cl = qfq_find_class(sch, skb->priority);
        if (cl != NULL)
            return cl;
    }

    *qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
    result = tc_classify(skb, q->filter_list, &res);
    if (result >= 0) {
#ifdef CONFIG_NET_CLS_ACT
        switch (result) {
        case TC_ACT_QUEUED:
        case TC_ACT_STOLEN:
            *qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
        case TC_ACT_SHOT:
            return NULL;
        }
#endif
        cl = (struct qfq_class *)res.class;
        if (cl == NULL)
            cl = qfq_find_class(sch, res.classid);
        return cl;
    }

    return NULL;
}

/* Generic comparison function, handling wraparound. */
static inline int qfq_gt(u64 a, u64 b)
{
    return (s64)(a - b) > 0;
}

/* Round a precise timestamp to its slotted value. */
static inline u64 qfq_round_down(u64 ts, unsigned int shift)
{
    return ts & ~((1ULL << shift) - 1);
}

/* return the pointer to the group with lowest index in the bitmap */
static inline struct qfq_group *qfq_ffs(struct qfq_sched *q,
                    unsigned long bitmap)
{
    int index = __ffs(bitmap);
    return &q->groups[index];
}
/* Calculate a mask to mimic what would be ffs_from(). */
static inline unsigned long mask_from(unsigned long bitmap, int from)
{
    return bitmap & ~((1UL << from) - 1);
}

/*
 * The state computation relies on ER=0, IR=1, EB=2, IB=3
 * First compute eligibility comparing grp->S, q->V,
 * then check if someone is blocking us and possibly add EB
 */
static int qfq_calc_state(struct qfq_sched *q, const struct qfq_group *grp)
{
    /* if S > V we are not eligible */
    unsigned int state = qfq_gt(grp->S, q->V);
    unsigned long mask = mask_from(q->bitmaps[ER], grp->index);
    struct qfq_group *next;

    if (mask) {
        next = qfq_ffs(q, mask);
        if (qfq_gt(grp->F, next->F))
            state |= EB;
    }

    return state;
}


/*
 * In principle
 *  q->bitmaps[dst] |= q->bitmaps[src] & mask;
 *  q->bitmaps[src] &= ~mask;
 * but we should make sure that src != dst
 */
static inline void qfq_move_groups(struct qfq_sched *q, unsigned long mask,
                   int src, int dst)
{
    q->bitmaps[dst] |= q->bitmaps[src] & mask;
    q->bitmaps[src] &= ~mask;
}

static void qfq_unblock_groups(struct qfq_sched *q, int index, u64 old_F)
{
    unsigned long mask = mask_from(q->bitmaps[ER], index + 1);
    struct qfq_group *next;

    if (mask) {
        next = qfq_ffs(q, mask);
        if (!qfq_gt(next->F, old_F))
            return;
    }

    mask = (1UL << index) - 1;
    qfq_move_groups(q, mask, EB, ER);
    qfq_move_groups(q, mask, IB, IR);
}

/*
 * perhaps
 *
    old_V ^= q->V;
    old_V >>= QFQ_MIN_SLOT_SHIFT;
    if (old_V) {
        ...
    }
 *
 */
static void qfq_make_eligible(struct qfq_sched *q, u64 old_V)
{
    unsigned long vslot = q->V >> QFQ_MIN_SLOT_SHIFT;
    unsigned long old_vslot = old_V >> QFQ_MIN_SLOT_SHIFT;

    if (vslot != old_vslot) {
        unsigned long mask = (1UL << fls(vslot ^ old_vslot)) - 1;
        qfq_move_groups(q, mask, IR, ER);
        qfq_move_groups(q, mask, IB, EB);
    }
}


/*
 * If the weight and lmax (max_pkt_size) of the classes do not change,
 * then QFQ guarantees that the slot index is never higher than
 * 2 + ((1<<QFQ_MTU_SHIFT)/QFQ_MIN_LMAX) * (QFQ_MAX_WEIGHT/QFQ_MAX_WSUM).
 *
 * With the current values of the above constants, the index is
 * then guaranteed to never be higher than 2 + 256 * (1 / 16) = 18.
 *
 * When the weight of a class is increased or the lmax of the class is
 * decreased, a new class with smaller slot size may happen to be
 * activated. The activation of this class should be properly delayed
 * to when the service of the class has finished in the ideal system
 * tracked by QFQ. If the activation of the class is not delayed to
 * this reference time instant, then this class may be unjustly served
 * before other classes waiting for service. This may cause
 * (unfrequently) the above bound to the slot index to be violated for
 * some of these unlucky classes.
 *
 * Instead of delaying the activation of the new class, which is quite
 * complex, the following inaccurate but simple solution is used: if
 * the slot index is higher than QFQ_MAX_SLOTS-2, then the timestamps
 * of the class are shifted backward so as to let the slot index
 * become equal to QFQ_MAX_SLOTS-2. This threshold is used because, if
 * the slot index is above it, then the data structure implementing
 * the bucket list either gets immediately corrupted or may get
 * corrupted on a possible next packet arrival that causes the start
 * time of the group to be shifted backward.
 */
static void qfq_slot_insert(struct qfq_group *grp, struct qfq_class *cl,
                u64 roundedS)
{
    u64 slot = (roundedS - grp->S) >> grp->slot_shift;
    unsigned int i; /* slot index in the bucket list */

    if (unlikely(slot > QFQ_MAX_SLOTS - 2)) {
        u64 deltaS = roundedS - grp->S -
            ((u64)(QFQ_MAX_SLOTS - 2)<<grp->slot_shift);
        cl->S -= deltaS;
        cl->F -= deltaS;
        slot = QFQ_MAX_SLOTS - 2;
    }

    i = (grp->front + slot) % QFQ_MAX_SLOTS;

    hlist_add_head(&cl->next, &grp->slots[i]);
    __set_bit(slot, &grp->full_slots);
}

/* Maybe introduce hlist_first_entry?? */
static struct qfq_class *qfq_slot_head(struct qfq_group *grp)
{
    return hlist_entry(grp->slots[grp->front].first,
               struct qfq_class, next);
}

/*
 * remove the entry from the slot
 */
static void qfq_front_slot_remove(struct qfq_group *grp)
{
    struct qfq_class *cl = qfq_slot_head(grp);

    BUG_ON(!cl);
    hlist_del(&cl->next);
    if (hlist_empty(&grp->slots[grp->front]))
        __clear_bit(0, &grp->full_slots);
}

/*
 * Returns the first full queue in a group. As a side effect,
 * adjust the bucket list so the first non-empty bucket is at
 * position 0 in full_slots.
 */
static struct qfq_class *qfq_slot_scan(struct qfq_group *grp)
{
    unsigned int i;

    pr_debug("qfq slot_scan: grp %u full %#lx\n",
         grp->index, grp->full_slots);

    if (grp->full_slots == 0)
        return NULL;

    i = __ffs(grp->full_slots);  /* zero based */
    if (i > 0) {
        grp->front = (grp->front + i) % QFQ_MAX_SLOTS;
        grp->full_slots >>= i;
    }

    return qfq_slot_head(grp);
}

/*
 * adjust the bucket list. When the start time of a group decreases,
 * we move the index down (modulo QFQ_MAX_SLOTS) so we don't need to
 * move the objects. The mask of occupied slots must be shifted
 * because we use ffs() to find the first non-empty slot.
 * This covers decreases in the group's start time, but what about
 * increases of the start time ?
 * Here too we should make sure that i is less than 32
 */
static void qfq_slot_rotate(struct qfq_group *grp, u64 roundedS)
{
    unsigned int i = (grp->S - roundedS) >> grp->slot_shift;

    grp->full_slots <<= i;
    grp->front = (grp->front - i) % QFQ_MAX_SLOTS;
}

static void qfq_update_eligible(struct qfq_sched *q, u64 old_V)
{
    struct qfq_group *grp;
    unsigned long ineligible;

    ineligible = q->bitmaps[IR] | q->bitmaps[IB];
    if (ineligible) {
        if (!q->bitmaps[ER]) {
            grp = qfq_ffs(q, ineligible);
            if (qfq_gt(grp->S, q->V))
                q->V = grp->S;
        }
        qfq_make_eligible(q, old_V);
    }
}

/*
 * Updates the class, returns true if also the group needs to be updated.
 */
static bool qfq_update_class(struct qfq_group *grp, struct qfq_class *cl)
{
    unsigned int len = qdisc_peek_len(cl->qdisc);

    cl->S = cl->F;
    if (!len)
        qfq_front_slot_remove(grp); /* queue is empty */
    else {
        u64 roundedS;

        cl->F = cl->S + (u64)len * cl->inv_w;
        roundedS = qfq_round_down(cl->S, grp->slot_shift);
        if (roundedS == grp->S)
            return false;

        qfq_front_slot_remove(grp);
        qfq_slot_insert(grp, cl, roundedS);
    }

    return true;
}

static struct sk_buff *qfq_dequeue(struct Qdisc *sch)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_group *grp;
    struct qfq_class *cl;
    struct sk_buff *skb;
    unsigned int len;
    u64 old_V;

    if (!q->bitmaps[ER])
        return NULL;

    grp = qfq_ffs(q, q->bitmaps[ER]);

    cl = qfq_slot_head(grp);
    skb = qdisc_dequeue_peeked(cl->qdisc);
    if (!skb) {
        WARN_ONCE(1, "qfq_dequeue: non-workconserving leaf\n");
        return NULL;
    }

    sch->q.qlen--;
    qdisc_bstats_update(sch, skb);

    old_V = q->V;
    len = qdisc_pkt_len(skb);
    q->V += (u64)len * IWSUM;
    pr_debug("qfq dequeue: len %u F %lld now %lld\n",
         len, (unsigned long long) cl->F, (unsigned long long) q->V);

    if (qfq_update_class(grp, cl)) {
        u64 old_F = grp->F;

        cl = qfq_slot_scan(grp);
        if (!cl)
            __clear_bit(grp->index, &q->bitmaps[ER]);
        else {
            u64 roundedS = qfq_round_down(cl->S, grp->slot_shift);
            unsigned int s;

            if (grp->S == roundedS)
                goto skip_unblock;
            grp->S = roundedS;
            grp->F = roundedS + (2ULL << grp->slot_shift);
            __clear_bit(grp->index, &q->bitmaps[ER]);
            s = qfq_calc_state(q, grp);
            __set_bit(grp->index, &q->bitmaps[s]);
        }

        qfq_unblock_groups(q, grp->index, old_F);
    }

skip_unblock:
    qfq_update_eligible(q, old_V);

    return skb;
}

/*
 * Assign a reasonable start time for a new flow k in group i.
 * Admissible values for \hat(F) are multiples of \sigma_i
 * no greater than V+\sigma_i . Larger values mean that
 * we had a wraparound so we consider the timestamp to be stale.
 *
 * If F is not stale and F >= V then we set S = F.
 * Otherwise we should assign S = V, but this may violate
 * the ordering in ER. So, if we have groups in ER, set S to
 * the F_j of the first group j which would be blocking us.
 * We are guaranteed not to move S backward because
 * otherwise our group i would still be blocked.
 */
static void qfq_update_start(struct qfq_sched *q, struct qfq_class *cl)
{
    unsigned long mask;
    u64 limit, roundedF;
    int slot_shift = cl->grp->slot_shift;

    roundedF = qfq_round_down(cl->F, slot_shift);
    limit = qfq_round_down(q->V, slot_shift) + (1ULL << slot_shift);

    if (!qfq_gt(cl->F, q->V) || qfq_gt(roundedF, limit)) {
        /* timestamp was stale */
        mask = mask_from(q->bitmaps[ER], cl->grp->index);
        if (mask) {
            struct qfq_group *next = qfq_ffs(q, mask);
            if (qfq_gt(roundedF, next->F)) {
                if (qfq_gt(limit, next->F))
                    cl->S = next->F;
                else /* preserve timestamp correctness */
                    cl->S = limit;
                return;
            }
        }
        cl->S = q->V;
    } else  /* timestamp is not stale */
        cl->S = cl->F;
}

static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_class *cl;
    int err = 0;

    cl = qfq_classify(skb, sch, &err);
    if (cl == NULL) {
        if (err & __NET_XMIT_BYPASS)
            sch->qstats.drops++;
        kfree_skb(skb);
        return err;
    }
    pr_debug("qfq_enqueue: cl = %x\n", cl->common.classid);

    if (unlikely(cl->lmax < qdisc_pkt_len(skb))) {
        pr_debug("qfq: increasing maxpkt from %u to %u for class %u",
              cl->lmax, qdisc_pkt_len(skb), cl->common.classid);
        qfq_update_reactivate_class(q, cl, cl->inv_w,
                        qdisc_pkt_len(skb), 0);
    }

    err = qdisc_enqueue(skb, cl->qdisc);
    if (unlikely(err != NET_XMIT_SUCCESS)) {
        pr_debug("qfq_enqueue: enqueue failed %d\n", err);
        if (net_xmit_drop_count(err)) {
            cl->qstats.drops++;
            sch->qstats.drops++;
        }
        return err;
    }

    bstats_update(&cl->bstats, skb);
    ++sch->q.qlen;

    /* If the new skb is not the head of queue, then done here. */
    if (cl->qdisc->q.qlen != 1)
        return err;

    /* If reach this point, queue q was idle */
    qfq_activate_class(q, cl, qdisc_pkt_len(skb));

    return err;
}

/*
 * Handle class switch from idle to backlogged.
 */
static void qfq_activate_class(struct qfq_sched *q, struct qfq_class *cl,
                   unsigned int pkt_len)
{
    struct qfq_group *grp = cl->grp;
    u64 roundedS;
    int s;

    qfq_update_start(q, cl);

    /* compute new finish time and rounded start. */
    cl->F = cl->S + (u64)pkt_len * cl->inv_w;
    roundedS = qfq_round_down(cl->S, grp->slot_shift);

    /*
     * insert cl in the correct bucket.
     * If cl->S >= grp->S we don't need to adjust the
     * bucket list and simply go to the insertion phase.
     * Otherwise grp->S is decreasing, we must make room
     * in the bucket list, and also recompute the group state.
     * Finally, if there were no flows in this group and nobody
     * was in ER make sure to adjust V.
     */
    if (grp->full_slots) {
        if (!qfq_gt(grp->S, cl->S))
            goto skip_update;

        /* create a slot for this cl->S */
        qfq_slot_rotate(grp, roundedS);
        /* group was surely ineligible, remove */
        __clear_bit(grp->index, &q->bitmaps[IR]);
        __clear_bit(grp->index, &q->bitmaps[IB]);
    } else if (!q->bitmaps[ER] && qfq_gt(roundedS, q->V))
        q->V = roundedS;

    grp->S = roundedS;
    grp->F = roundedS + (2ULL << grp->slot_shift);
    s = qfq_calc_state(q, grp);
    __set_bit(grp->index, &q->bitmaps[s]);

    pr_debug("qfq enqueue: new state %d %#lx S %lld F %lld V %lld\n",
         s, q->bitmaps[s],
         (unsigned long long) cl->S,
         (unsigned long long) cl->F,
         (unsigned long long) q->V);

skip_update:
    qfq_slot_insert(grp, cl, roundedS);
}


static void qfq_slot_remove(struct qfq_sched *q, struct qfq_group *grp,
                struct qfq_class *cl)
{
    unsigned int i, offset;
    u64 roundedS;

    roundedS = qfq_round_down(cl->S, grp->slot_shift);
    offset = (roundedS - grp->S) >> grp->slot_shift;
    i = (grp->front + offset) % QFQ_MAX_SLOTS;

    hlist_del(&cl->next);
    if (hlist_empty(&grp->slots[i]))
        __clear_bit(offset, &grp->full_slots);
}

/*
 * called to forcibly destroy a queue.
 * If the queue is not in the front bucket, or if it has
 * other queues in the front bucket, we can simply remove
 * the queue with no other side effects.
 * Otherwise we must propagate the event up.
 */
static void qfq_deactivate_class(struct qfq_sched *q, struct qfq_class *cl)
{
    struct qfq_group *grp = cl->grp;
    unsigned long mask;
    u64 roundedS;
    int s;

    cl->F = cl->S;
    qfq_slot_remove(q, grp, cl);

    if (!grp->full_slots) {
        __clear_bit(grp->index, &q->bitmaps[IR]);
        __clear_bit(grp->index, &q->bitmaps[EB]);
        __clear_bit(grp->index, &q->bitmaps[IB]);

        if (test_bit(grp->index, &q->bitmaps[ER]) &&
            !(q->bitmaps[ER] & ~((1UL << grp->index) - 1))) {
            mask = q->bitmaps[ER] & ((1UL << grp->index) - 1);
            if (mask)
                mask = ~((1UL << __fls(mask)) - 1);
            else
                mask = ~0UL;
            qfq_move_groups(q, mask, EB, ER);
            qfq_move_groups(q, mask, IB, IR);
        }
        __clear_bit(grp->index, &q->bitmaps[ER]);
    } else if (hlist_empty(&grp->slots[grp->front])) {
        cl = qfq_slot_scan(grp);
        roundedS = qfq_round_down(cl->S, grp->slot_shift);
        if (grp->S != roundedS) {
            __clear_bit(grp->index, &q->bitmaps[ER]);
            __clear_bit(grp->index, &q->bitmaps[IR]);
            __clear_bit(grp->index, &q->bitmaps[EB]);
            __clear_bit(grp->index, &q->bitmaps[IB]);
            grp->S = roundedS;
            grp->F = roundedS + (2ULL << grp->slot_shift);
            s = qfq_calc_state(q, grp);
            __set_bit(grp->index, &q->bitmaps[s]);
        }
    }

    qfq_update_eligible(q, q->V);
}

static void qfq_qlen_notify(struct Qdisc *sch, unsigned long arg)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_class *cl = (struct qfq_class *)arg;

    if (cl->qdisc->q.qlen == 0)
        qfq_deactivate_class(q, cl);
}

static unsigned int qfq_drop(struct Qdisc *sch)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_group *grp;
    unsigned int i, j, len;

    for (i = 0; i <= QFQ_MAX_INDEX; i++) {
        grp = &q->groups[i];
        for (j = 0; j < QFQ_MAX_SLOTS; j++) {
            struct qfq_class *cl;
            struct hlist_node *n;

            hlist_for_each_entry(cl, n, &grp->slots[j], next) {

                if (!cl->qdisc->ops->drop)
                    continue;

                len = cl->qdisc->ops->drop(cl->qdisc);
                if (len > 0) {
                    sch->q.qlen--;
                    if (!cl->qdisc->q.qlen)
                        qfq_deactivate_class(q, cl);

                    return len;
                }
            }
        }
    }

    return 0;
}

static int qfq_init_qdisc(struct Qdisc *sch, struct nlattr *opt)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_group *grp;
    int i, j, err;

    err = qdisc_class_hash_init(&q->clhash);
    if (err < 0)
        return err;

    for (i = 0; i <= QFQ_MAX_INDEX; i++) {
        grp = &q->groups[i];
        grp->index = i;
        grp->slot_shift = QFQ_MTU_SHIFT + FRAC_BITS
                   - (QFQ_MAX_INDEX - i);
        for (j = 0; j < QFQ_MAX_SLOTS; j++)
            INIT_HLIST_HEAD(&grp->slots[j]);
    }

    return 0;
}

static void qfq_reset_qdisc(struct Qdisc *sch)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_group *grp;
    struct qfq_class *cl;
    struct hlist_node *n, *tmp;
    unsigned int i, j;

    for (i = 0; i <= QFQ_MAX_INDEX; i++) {
        grp = &q->groups[i];
        for (j = 0; j < QFQ_MAX_SLOTS; j++) {
            hlist_for_each_entry_safe(cl, n, tmp,
                          &grp->slots[j], next) {
                qfq_deactivate_class(q, cl);
            }
        }
    }

    for (i = 0; i < q->clhash.hashsize; i++) {
        hlist_for_each_entry(cl, n, &q->clhash.hash[i], common.hnode)
            qdisc_reset(cl->qdisc);
    }
    sch->q.qlen = 0;
}

static void qfq_destroy_qdisc(struct Qdisc *sch)
{
    struct qfq_sched *q = qdisc_priv(sch);
    struct qfq_class *cl;
    struct hlist_node *n, *next;
    unsigned int i;

    tcf_destroy_chain(&q->filter_list);

    for (i = 0; i < q->clhash.hashsize; i++) {
        hlist_for_each_entry_safe(cl, n, next, &q->clhash.hash[i],
                      common.hnode) {
            qfq_destroy_class(sch, cl);
        }
    }
    qdisc_class_hash_destroy(&q->clhash);
}

static const struct Qdisc_class_ops qfq_class_ops = {
    .change     = qfq_change_class,
    .delete     = qfq_delete_class,
    .get        = qfq_get_class,
    .put        = qfq_put_class,
    .tcf_chain  = qfq_tcf_chain,
    .bind_tcf   = qfq_bind_tcf,
    .unbind_tcf = qfq_unbind_tcf,
    .graft      = qfq_graft_class,
    .leaf       = qfq_class_leaf,
    .qlen_notify    = qfq_qlen_notify,
    .dump       = qfq_dump_class,
    .dump_stats = qfq_dump_class_stats,
    .walk       = qfq_walk,
};

static struct Qdisc_ops qfq_qdisc_ops __read_mostly = {
    .cl_ops     = &qfq_class_ops,
    .id     = "qfq",
    .priv_size  = sizeof(struct qfq_sched),
    .enqueue    = qfq_enqueue,
    .dequeue    = qfq_dequeue,
    .peek       = qdisc_peek_dequeued,
    .drop       = qfq_drop,
    .init       = qfq_init_qdisc,
    .reset      = qfq_reset_qdisc,
    .destroy    = qfq_destroy_qdisc,
    .owner      = THIS_MODULE,
};

static int __init qfq_init(void)
{
    return register_qdisc(&qfq_qdisc_ops);
}

static void __exit qfq_exit(void)
{
    unregister_qdisc(&qfq_qdisc_ops);
}

module_init(qfq_init);
module_exit(qfq_exit);
MODULE_LICENSE("GPL");