sch_codel.c

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/*
 * Codel - The Controlled-Delay Active Queue Management algorithm
 *
 *  Copyright (C) 2011-2012 Kathleen Nichols <[email protected]>
 *  Copyright (C) 2011-2012 Van Jacobson <[email protected]>
 *
 *  Implemented on linux by :
 *  Copyright (C) 2012 Michael D. Taht <[email protected]>
 *  Copyright (C) 2012 Eric Dumazet <[email protected]>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions, and the following disclaimer,
 *    without modification.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The names of the authors may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * Alternatively, provided that this notice is retained in full, this
 * software may be distributed under the terms of the GNU General
 * Public License ("GPL") version 2, in which case the provisions of the
 * GPL apply INSTEAD OF those given above.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 *
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <linux/prefetch.h>
#include <net/pkt_sched.h>
#include <net/codel.h>


#define DEFAULT_CODEL_LIMIT 1000

struct codel_sched_data {
    struct codel_params params;
    struct codel_vars   vars;
    struct codel_stats  stats;
    u32         drop_overlimit;
};

/* This is the specific function called from codel_dequeue()
 * to dequeue a packet from queue. Note: backlog is handled in
 * codel, we dont need to reduce it here.
 */
static struct sk_buff *dequeue(struct codel_vars *vars, struct Qdisc *sch)
{
    struct sk_buff *skb = __skb_dequeue(&sch->q);

    prefetch(&skb->end); /* we'll need skb_shinfo() */
    return skb;
}

static struct sk_buff *codel_qdisc_dequeue(struct Qdisc *sch)
{
    struct codel_sched_data *q = qdisc_priv(sch);
    struct sk_buff *skb;

    skb = codel_dequeue(sch, &q->params, &q->vars, &q->stats, dequeue);

    /* We cant call qdisc_tree_decrease_qlen() if our qlen is 0,
     * or HTB crashes. Defer it for next round.
     */
    if (q->stats.drop_count && sch->q.qlen) {
        qdisc_tree_decrease_qlen(sch, q->stats.drop_count);
        q->stats.drop_count = 0;
    }
    if (skb)
        qdisc_bstats_update(sch, skb);
    return skb;
}

static int codel_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
    struct codel_sched_data *q;

    if (likely(qdisc_qlen(sch) < sch->limit)) {
        codel_set_enqueue_time(skb);
        return qdisc_enqueue_tail(skb, sch);
    }
    q = qdisc_priv(sch);
    q->drop_overlimit++;
    return qdisc_drop(skb, sch);
}

static const struct nla_policy codel_policy[TCA_CODEL_MAX + 1] = {
    [TCA_CODEL_TARGET]  = { .type = NLA_U32 },
    [TCA_CODEL_LIMIT]   = { .type = NLA_U32 },
    [TCA_CODEL_INTERVAL]    = { .type = NLA_U32 },
    [TCA_CODEL_ECN]     = { .type = NLA_U32 },
};

static int codel_change(struct Qdisc *sch, struct nlattr *opt)
{
    struct codel_sched_data *q = qdisc_priv(sch);
    struct nlattr *tb[TCA_CODEL_MAX + 1];
    unsigned int qlen;
    int err;

    if (!opt)
        return -EINVAL;

    err = nla_parse_nested(tb, TCA_CODEL_MAX, opt, codel_policy);
    if (err < 0)
        return err;

    sch_tree_lock(sch);

    if (tb[TCA_CODEL_TARGET]) {
        u32 target = nla_get_u32(tb[TCA_CODEL_TARGET]);

        q->params.target = ((u64)target * NSEC_PER_USEC) >> CODEL_SHIFT;
    }

    if (tb[TCA_CODEL_INTERVAL]) {
        u32 interval = nla_get_u32(tb[TCA_CODEL_INTERVAL]);

        q->params.interval = ((u64)interval * NSEC_PER_USEC) >> CODEL_SHIFT;
    }

    if (tb[TCA_CODEL_LIMIT])
        sch->limit = nla_get_u32(tb[TCA_CODEL_LIMIT]);

    if (tb[TCA_CODEL_ECN])
        q->params.ecn = !!nla_get_u32(tb[TCA_CODEL_ECN]);

    qlen = sch->q.qlen;
    while (sch->q.qlen > sch->limit) {
        struct sk_buff *skb = __skb_dequeue(&sch->q);

        sch->qstats.backlog -= qdisc_pkt_len(skb);
        qdisc_drop(skb, sch);
    }
    qdisc_tree_decrease_qlen(sch, qlen - sch->q.qlen);

    sch_tree_unlock(sch);
    return 0;
}

static int codel_init(struct Qdisc *sch, struct nlattr *opt)
{
    struct codel_sched_data *q = qdisc_priv(sch);

    sch->limit = DEFAULT_CODEL_LIMIT;

    codel_params_init(&q->params);
    codel_vars_init(&q->vars);
    codel_stats_init(&q->stats);

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

        if (err)
            return err;
    }

    if (sch->limit >= 1)
        sch->flags |= TCQ_F_CAN_BYPASS;
    else
        sch->flags &= ~TCQ_F_CAN_BYPASS;

    return 0;
}

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

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

    if (nla_put_u32(skb, TCA_CODEL_TARGET,
            codel_time_to_us(q->params.target)) ||
        nla_put_u32(skb, TCA_CODEL_LIMIT,
            sch->limit) ||
        nla_put_u32(skb, TCA_CODEL_INTERVAL,
            codel_time_to_us(q->params.interval)) ||
        nla_put_u32(skb, TCA_CODEL_ECN,
            q->params.ecn))
        goto nla_put_failure;

    return nla_nest_end(skb, opts);

nla_put_failure:
    nla_nest_cancel(skb, opts);
    return -1;
}

static int codel_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
{
    const struct codel_sched_data *q = qdisc_priv(sch);
    struct tc_codel_xstats st = {
        .maxpacket  = q->stats.maxpacket,
        .count      = q->vars.count,
        .lastcount  = q->vars.lastcount,
        .drop_overlimit = q->drop_overlimit,
        .ldelay     = codel_time_to_us(q->vars.ldelay),
        .dropping   = q->vars.dropping,
        .ecn_mark   = q->stats.ecn_mark,
    };

    if (q->vars.dropping) {
        codel_tdiff_t delta = q->vars.drop_next - codel_get_time();

        if (delta >= 0)
            st.drop_next = codel_time_to_us(delta);
        else
            st.drop_next = -codel_time_to_us(-delta);
    }

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

static void codel_reset(struct Qdisc *sch)
{
    struct codel_sched_data *q = qdisc_priv(sch);

    qdisc_reset_queue(sch);
    codel_vars_init(&q->vars);
}

static struct Qdisc_ops codel_qdisc_ops __read_mostly = {
    .id     =   "codel",
    .priv_size  =   sizeof(struct codel_sched_data),

    .enqueue    =   codel_qdisc_enqueue,
    .dequeue    =   codel_qdisc_dequeue,
    .peek       =   qdisc_peek_dequeued,
    .init       =   codel_init,
    .reset      =   codel_reset,
    .change     =   codel_change,
    .dump       =   codel_dump,
    .dump_stats =   codel_dump_stats,
    .owner      =   THIS_MODULE,
};

static int __init codel_module_init(void)
{
    return register_qdisc(&codel_qdisc_ops);
}

static void __exit codel_module_exit(void)
{
    unregister_qdisc(&codel_qdisc_ops);
}

module_init(codel_module_init)
module_exit(codel_module_exit)

MODULE_DESCRIPTION("Controlled Delay queue discipline");
MODULE_AUTHOR("Dave Taht");
MODULE_AUTHOR("Eric Dumazet");
MODULE_LICENSE("Dual BSD/GPL");