![Eric Dumazet](/assets/img/avatar_default.png)
Qdisc performance suffers when packets are dropped at enqueue() time because drops (kfree_skb()) are done while qdisc lock is held, delaying a dequeue() draining the queue. Nominal throughput can be reduced by 50 % when this happens, at a time we would like the dequeue() to proceed as fast as possible. Even FQ is vulnerable to this problem, while one of FQ goals was to provide some flow isolation. This patch adds a 'struct sk_buff **to_free' parameter to all qdisc->enqueue(), and in qdisc_drop() helper. I measured a performance increase of up to 12 %, but this patch is a prereq so that future batches in enqueue() can fly. Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
308 lines
8.4 KiB
C
308 lines
8.4 KiB
C
/*
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* Codel - The Controlled-Delay Active Queue Management algorithm
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*
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* Copyright (C) 2011-2012 Kathleen Nichols <nichols@pollere.com>
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* Copyright (C) 2011-2012 Van Jacobson <van@pollere.net>
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*
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* Implemented on linux by :
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* Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net>
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* Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions, and the following disclaimer,
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* without modification.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The names of the authors may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* Alternatively, provided that this notice is retained in full, this
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* software may be distributed under the terms of the GNU General
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* Public License ("GPL") version 2, in which case the provisions of the
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* GPL apply INSTEAD OF those given above.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*
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*/
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/errno.h>
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#include <linux/skbuff.h>
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#include <linux/prefetch.h>
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#include <net/pkt_sched.h>
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#include <net/codel.h>
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#include <net/codel_impl.h>
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#include <net/codel_qdisc.h>
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#define DEFAULT_CODEL_LIMIT 1000
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struct codel_sched_data {
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struct codel_params params;
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struct codel_vars vars;
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struct codel_stats stats;
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u32 drop_overlimit;
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};
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/* This is the specific function called from codel_dequeue()
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* to dequeue a packet from queue. Note: backlog is handled in
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* codel, we dont need to reduce it here.
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*/
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static struct sk_buff *dequeue_func(struct codel_vars *vars, void *ctx)
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{
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struct Qdisc *sch = ctx;
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struct sk_buff *skb = __skb_dequeue(&sch->q);
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if (skb)
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sch->qstats.backlog -= qdisc_pkt_len(skb);
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prefetch(&skb->end); /* we'll need skb_shinfo() */
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return skb;
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}
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static void drop_func(struct sk_buff *skb, void *ctx)
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{
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struct Qdisc *sch = ctx;
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kfree_skb(skb);
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qdisc_qstats_drop(sch);
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}
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static struct sk_buff *codel_qdisc_dequeue(struct Qdisc *sch)
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{
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struct codel_sched_data *q = qdisc_priv(sch);
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struct sk_buff *skb;
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skb = codel_dequeue(sch, &sch->qstats.backlog, &q->params, &q->vars,
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&q->stats, qdisc_pkt_len, codel_get_enqueue_time,
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drop_func, dequeue_func);
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/* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
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* or HTB crashes. Defer it for next round.
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*/
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if (q->stats.drop_count && sch->q.qlen) {
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qdisc_tree_reduce_backlog(sch, q->stats.drop_count, q->stats.drop_len);
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q->stats.drop_count = 0;
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q->stats.drop_len = 0;
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}
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if (skb)
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qdisc_bstats_update(sch, skb);
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return skb;
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}
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static int codel_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
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struct sk_buff **to_free)
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{
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struct codel_sched_data *q;
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if (likely(qdisc_qlen(sch) < sch->limit)) {
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codel_set_enqueue_time(skb);
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return qdisc_enqueue_tail(skb, sch);
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}
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q = qdisc_priv(sch);
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q->drop_overlimit++;
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return qdisc_drop(skb, sch, to_free);
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}
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static const struct nla_policy codel_policy[TCA_CODEL_MAX + 1] = {
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[TCA_CODEL_TARGET] = { .type = NLA_U32 },
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[TCA_CODEL_LIMIT] = { .type = NLA_U32 },
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[TCA_CODEL_INTERVAL] = { .type = NLA_U32 },
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[TCA_CODEL_ECN] = { .type = NLA_U32 },
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[TCA_CODEL_CE_THRESHOLD]= { .type = NLA_U32 },
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};
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static int codel_change(struct Qdisc *sch, struct nlattr *opt)
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{
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struct codel_sched_data *q = qdisc_priv(sch);
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struct nlattr *tb[TCA_CODEL_MAX + 1];
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unsigned int qlen, dropped = 0;
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int err;
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if (!opt)
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return -EINVAL;
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err = nla_parse_nested(tb, TCA_CODEL_MAX, opt, codel_policy);
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if (err < 0)
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return err;
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sch_tree_lock(sch);
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if (tb[TCA_CODEL_TARGET]) {
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u32 target = nla_get_u32(tb[TCA_CODEL_TARGET]);
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q->params.target = ((u64)target * NSEC_PER_USEC) >> CODEL_SHIFT;
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}
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if (tb[TCA_CODEL_CE_THRESHOLD]) {
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u64 val = nla_get_u32(tb[TCA_CODEL_CE_THRESHOLD]);
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q->params.ce_threshold = (val * NSEC_PER_USEC) >> CODEL_SHIFT;
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}
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if (tb[TCA_CODEL_INTERVAL]) {
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u32 interval = nla_get_u32(tb[TCA_CODEL_INTERVAL]);
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q->params.interval = ((u64)interval * NSEC_PER_USEC) >> CODEL_SHIFT;
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}
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if (tb[TCA_CODEL_LIMIT])
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sch->limit = nla_get_u32(tb[TCA_CODEL_LIMIT]);
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if (tb[TCA_CODEL_ECN])
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q->params.ecn = !!nla_get_u32(tb[TCA_CODEL_ECN]);
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qlen = sch->q.qlen;
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while (sch->q.qlen > sch->limit) {
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struct sk_buff *skb = __skb_dequeue(&sch->q);
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dropped += qdisc_pkt_len(skb);
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qdisc_qstats_backlog_dec(sch, skb);
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rtnl_qdisc_drop(skb, sch);
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}
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qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped);
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sch_tree_unlock(sch);
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return 0;
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}
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static int codel_init(struct Qdisc *sch, struct nlattr *opt)
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{
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struct codel_sched_data *q = qdisc_priv(sch);
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sch->limit = DEFAULT_CODEL_LIMIT;
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codel_params_init(&q->params);
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codel_vars_init(&q->vars);
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codel_stats_init(&q->stats);
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q->params.mtu = psched_mtu(qdisc_dev(sch));
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if (opt) {
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int err = codel_change(sch, opt);
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if (err)
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return err;
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}
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if (sch->limit >= 1)
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sch->flags |= TCQ_F_CAN_BYPASS;
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else
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sch->flags &= ~TCQ_F_CAN_BYPASS;
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return 0;
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}
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static int codel_dump(struct Qdisc *sch, struct sk_buff *skb)
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{
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struct codel_sched_data *q = qdisc_priv(sch);
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struct nlattr *opts;
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opts = nla_nest_start(skb, TCA_OPTIONS);
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if (opts == NULL)
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goto nla_put_failure;
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if (nla_put_u32(skb, TCA_CODEL_TARGET,
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codel_time_to_us(q->params.target)) ||
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nla_put_u32(skb, TCA_CODEL_LIMIT,
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sch->limit) ||
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nla_put_u32(skb, TCA_CODEL_INTERVAL,
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codel_time_to_us(q->params.interval)) ||
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nla_put_u32(skb, TCA_CODEL_ECN,
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q->params.ecn))
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goto nla_put_failure;
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if (q->params.ce_threshold != CODEL_DISABLED_THRESHOLD &&
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nla_put_u32(skb, TCA_CODEL_CE_THRESHOLD,
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codel_time_to_us(q->params.ce_threshold)))
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goto nla_put_failure;
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return nla_nest_end(skb, opts);
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nla_put_failure:
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nla_nest_cancel(skb, opts);
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return -1;
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}
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static int codel_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
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{
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const struct codel_sched_data *q = qdisc_priv(sch);
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struct tc_codel_xstats st = {
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.maxpacket = q->stats.maxpacket,
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.count = q->vars.count,
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.lastcount = q->vars.lastcount,
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.drop_overlimit = q->drop_overlimit,
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.ldelay = codel_time_to_us(q->vars.ldelay),
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.dropping = q->vars.dropping,
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.ecn_mark = q->stats.ecn_mark,
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.ce_mark = q->stats.ce_mark,
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};
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if (q->vars.dropping) {
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codel_tdiff_t delta = q->vars.drop_next - codel_get_time();
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if (delta >= 0)
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st.drop_next = codel_time_to_us(delta);
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else
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st.drop_next = -codel_time_to_us(-delta);
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}
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return gnet_stats_copy_app(d, &st, sizeof(st));
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}
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static void codel_reset(struct Qdisc *sch)
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{
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struct codel_sched_data *q = qdisc_priv(sch);
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qdisc_reset_queue(sch);
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codel_vars_init(&q->vars);
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}
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static struct Qdisc_ops codel_qdisc_ops __read_mostly = {
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.id = "codel",
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.priv_size = sizeof(struct codel_sched_data),
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.enqueue = codel_qdisc_enqueue,
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.dequeue = codel_qdisc_dequeue,
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.peek = qdisc_peek_dequeued,
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.init = codel_init,
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.reset = codel_reset,
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.change = codel_change,
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.dump = codel_dump,
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.dump_stats = codel_dump_stats,
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.owner = THIS_MODULE,
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};
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static int __init codel_module_init(void)
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{
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return register_qdisc(&codel_qdisc_ops);
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}
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static void __exit codel_module_exit(void)
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{
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unregister_qdisc(&codel_qdisc_ops);
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}
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module_init(codel_module_init)
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module_exit(codel_module_exit)
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MODULE_DESCRIPTION("Controlled Delay queue discipline");
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MODULE_AUTHOR("Dave Taht");
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MODULE_AUTHOR("Eric Dumazet");
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MODULE_LICENSE("Dual BSD/GPL");
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