/* Copyright (C) 2013 Cisco Systems, Inc, 2013. * * 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. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * Author: Vijay Subramanian <vijaynsu@cisco.com> * Author: Mythili Prabhu <mysuryan@cisco.com> * * ECN support is added by Naeem Khademi <naeemk@ifi.uio.no> * University of Oslo, Norway. * * References: * IETF draft submission: http://tools.ietf.org/html/draft-pan-aqm-pie-00 * IEEE Conference on High Performance Switching and Routing 2013 : * "PIE: A * Lightweight Control Scheme to Address the Bufferbloat Problem" */ #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 <net/pkt_sched.h> #include <net/inet_ecn.h> #define QUEUE_THRESHOLD 10000 #define DQCOUNT_INVALID -1 #define MAX_PROB 0xffffffff #define PIE_SCALE 8 /* parameters used */ struct pie_params { psched_time_t target; /* user specified target delay in pschedtime */ u32 tupdate; /* timer frequency (in jiffies) */ u32 limit; /* number of packets that can be enqueued */ u32 alpha; /* alpha and beta are between 0 and 32 */ u32 beta; /* and are used for shift relative to 1 */ bool ecn; /* true if ecn is enabled */ bool bytemode; /* to scale drop early prob based on pkt size */ }; /* variables used */ struct pie_vars { u32 prob; /* probability but scaled by u32 limit. */ psched_time_t burst_time; psched_time_t qdelay; psched_time_t qdelay_old; u64 dq_count; /* measured in bytes */ psched_time_t dq_tstamp; /* drain rate */ u32 avg_dq_rate; /* bytes per pschedtime tick,scaled */ u32 qlen_old; /* in bytes */ }; /* statistics gathering */ struct pie_stats { u32 packets_in; /* total number of packets enqueued */ u32 dropped; /* packets dropped due to pie_action */ u32 overlimit; /* dropped due to lack of space in queue */ u32 maxq; /* maximum queue size */ u32 ecn_mark; /* packets marked with ECN */ }; /* private data for the Qdisc */ struct pie_sched_data { struct pie_params params; struct pie_vars vars; struct pie_stats stats; struct timer_list adapt_timer; }; static void pie_params_init(struct pie_params *params) { params->alpha = 2; params->beta = 20; params->tupdate = usecs_to_jiffies(30 * USEC_PER_MSEC); /* 30 ms */ params->limit = 1000; /* default of 1000 packets */ params->target = PSCHED_NS2TICKS(20 * NSEC_PER_MSEC); /* 20 ms */ params->ecn = false; params->bytemode = false; } static void pie_vars_init(struct pie_vars *vars) { vars->dq_count = DQCOUNT_INVALID; vars->avg_dq_rate = 0; /* default of 100 ms in pschedtime */ vars->burst_time = PSCHED_NS2TICKS(100 * NSEC_PER_MSEC); } static bool drop_early(struct Qdisc *sch, u32 packet_size) { struct pie_sched_data *q = qdisc_priv(sch); u32 rnd; u32 local_prob = q->vars.prob; u32 mtu = psched_mtu(qdisc_dev(sch)); /* If there is still burst allowance left skip random early drop */ if (q->vars.burst_time > 0) return false; /* If current delay is less than half of target, and * if drop prob is low already, disable early_drop */ if ((q->vars.qdelay < q->params.target / 2) && (q->vars.prob < MAX_PROB / 5)) return false; /* If we have fewer than 2 mtu-sized packets, disable drop_early, * similar to min_th in RED */ if (sch->qstats.backlog < 2 * mtu) return false; /* If bytemode is turned on, use packet size to compute new * probablity. Smaller packets will have lower drop prob in this case */ if (q->params.bytemode && packet_size <= mtu) local_prob = (local_prob / mtu) * packet_size; else local_prob = q->vars.prob; rnd = prandom_u32(); if (rnd < local_prob) return true; return false; } static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch) { struct pie_sched_data *q = qdisc_priv(sch); bool enqueue = false; if (unlikely(qdisc_qlen(sch) >= sch->limit)) { q->stats.overlimit++; goto out; } if (!drop_early(sch, skb->len)) { enqueue = true; } else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) && INET_ECN_set_ce(skb)) { /* If packet is ecn capable, mark it if drop probability * is lower than 10%, else drop it. */ q->stats.ecn_mark++; enqueue = true; } /* we can enqueue the packet */ if (enqueue) { q->stats.packets_in++; if (qdisc_qlen(sch) > q->stats.maxq) q->stats.maxq = qdisc_qlen(sch); return qdisc_enqueue_tail(skb, sch); } out: q->stats.dropped++; return qdisc_drop(skb, sch); } static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = { [TCA_PIE_TARGET] = {.type = NLA_U32}, [TCA_PIE_LIMIT] = {.type = NLA_U32}, [TCA_PIE_TUPDATE] = {.type = NLA_U32}, [TCA_PIE_ALPHA] = {.type = NLA_U32}, [TCA_PIE_BETA] = {.type = NLA_U32}, [TCA_PIE_ECN] = {.type = NLA_U32}, [TCA_PIE_BYTEMODE] = {.type = NLA_U32}, }; static int pie_change(struct Qdisc *sch, struct nlattr *opt) { struct pie_sched_data *q = qdisc_priv(sch); struct nlattr *tb[TCA_PIE_MAX + 1]; unsigned int qlen; int err; if (!opt) return -EINVAL; err = nla_parse_nested(tb, TCA_PIE_MAX, opt, pie_policy); if (err < 0) return err; sch_tree_lock(sch); /* convert from microseconds to pschedtime */ if (tb[TCA_PIE_TARGET]) { /* target is in us */ u32 target = nla_get_u32(tb[TCA_PIE_TARGET]); /* convert to pschedtime */ q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC); } /* tupdate is in jiffies */ if (tb[TCA_PIE_TUPDATE]) q->params.tupdate = usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE])); if (tb[TCA_PIE_LIMIT]) { u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]); q->params.limit = limit; sch->limit = limit; } if (tb[TCA_PIE_ALPHA]) q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]); if (tb[TCA_PIE_BETA]) q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]); if (tb[TCA_PIE_ECN]) q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]); if (tb[TCA_PIE_BYTEMODE]) q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]); /* Drop excess packets if new limit is lower */ qlen = sch->q.qlen; while (sch->q.qlen > sch->limit) { struct sk_buff *skb = __skb_dequeue(&sch->q); qdisc_qstats_backlog_dec(sch, skb); qdisc_drop(skb, sch); } qdisc_tree_decrease_qlen(sch, qlen - sch->q.qlen); sch_tree_unlock(sch); return 0; } static void pie_process_dequeue(struct Qdisc *sch, struct sk_buff *skb) { struct pie_sched_data *q = qdisc_priv(sch); int qlen = sch->qstats.backlog; /* current queue size in bytes */ /* If current queue is about 10 packets or more and dq_count is unset * we have enough packets to calculate the drain rate. Save * current time as dq_tstamp and start measurement cycle. */ if (qlen >= QUEUE_THRESHOLD && q->vars.dq_count == DQCOUNT_INVALID) { q->vars.dq_tstamp = psched_get_time(); q->vars.dq_count = 0; } /* Calculate the average drain rate from this value. If queue length * has receded to a small value viz., <= QUEUE_THRESHOLD bytes,reset * the dq_count to -1 as we don't have enough packets to calculate the * drain rate anymore The following if block is entered only when we * have a substantial queue built up (QUEUE_THRESHOLD bytes or more) * and we calculate the drain rate for the threshold here. dq_count is * in bytes, time difference in psched_time, hence rate is in * bytes/psched_time. */ if (q->vars.dq_count != DQCOUNT_INVALID) { q->vars.dq_count += skb->len; if (q->vars.dq_count >= QUEUE_THRESHOLD) { psched_time_t now = psched_get_time(); u32 dtime = now - q->vars.dq_tstamp; u32 count = q->vars.dq_count << PIE_SCALE; if (dtime == 0) return; count = count / dtime; if (q->vars.avg_dq_rate == 0) q->vars.avg_dq_rate = count; else q->vars.avg_dq_rate = (q->vars.avg_dq_rate - (q->vars.avg_dq_rate >> 3)) + (count >> 3); /* If the queue has receded below the threshold, we hold * on to the last drain rate calculated, else we reset * dq_count to 0 to re-enter the if block when the next * packet is dequeued */ if (qlen < QUEUE_THRESHOLD) q->vars.dq_count = DQCOUNT_INVALID; else { q->vars.dq_count = 0; q->vars.dq_tstamp = psched_get_time(); } if (q->vars.burst_time > 0) { if (q->vars.burst_time > dtime) q->vars.burst_time -= dtime; else q->vars.burst_time = 0; } } } } static void calculate_probability(struct Qdisc *sch) { struct pie_sched_data *q = qdisc_priv(sch); u32 qlen = sch->qstats.backlog; /* queue size in bytes */ psched_time_t qdelay = 0; /* in pschedtime */ psched_time_t qdelay_old = q->vars.qdelay; /* in pschedtime */ s32 delta = 0; /* determines the change in probability */ u32 oldprob; u32 alpha, beta; bool update_prob = true; q->vars.qdelay_old = q->vars.qdelay; if (q->vars.avg_dq_rate > 0) qdelay = (qlen << PIE_SCALE) / q->vars.avg_dq_rate; else qdelay = 0; /* If qdelay is zero and qlen is not, it means qlen is very small, less * than dequeue_rate, so we do not update probabilty in this round */ if (qdelay == 0 && qlen != 0) update_prob = false; /* In the algorithm, alpha and beta are between 0 and 2 with typical * value for alpha as 0.125. In this implementation, we use values 0-32 * passed from user space to represent this. Also, alpha and beta have * unit of HZ and need to be scaled before they can used to update * probability. alpha/beta are updated locally below by 1) scaling them * appropriately 2) scaling down by 16 to come to 0-2 range. * Please see paper for details. * * We scale alpha and beta differently depending on whether we are in * light, medium or high dropping mode. */ if (q->vars.prob < MAX_PROB / 100) { alpha = (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7; beta = (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7; } else if (q->vars.prob < MAX_PROB / 10) { alpha = (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5; beta = (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5; } else { alpha = (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; beta = (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; } /* alpha and beta should be between 0 and 32, in multiples of 1/16 */ delta += alpha * ((qdelay - q->params.target)); delta += beta * ((qdelay - qdelay_old)); oldprob = q->vars.prob; /* to ensure we increase probability in steps of no more than 2% */ if (delta > (s32) (MAX_PROB / (100 / 2)) && q->vars.prob >= MAX_PROB / 10) delta = (MAX_PROB / 100) * 2; /* Non-linear drop: * Tune drop probability to increase quickly for high delays(>= 250ms) * 250ms is derived through experiments and provides error protection */ if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC))) delta += MAX_PROB / (100 / 2); q->vars.prob += delta; if (delta > 0) { /* prevent overflow */ if (q->vars.prob < oldprob) { q->vars.prob = MAX_PROB; /* Prevent normalization error. If probability is at * maximum value already, we normalize it here, and * skip the check to do a non-linear drop in the next * section. */ update_prob = false; } } else { /* prevent underflow */ if (q->vars.prob > oldprob) q->vars.prob = 0; } /* Non-linear drop in probability: Reduce drop probability quickly if * delay is 0 for 2 consecutive Tupdate periods. */ if ((qdelay == 0) && (qdelay_old == 0) && update_prob) q->vars.prob = (q->vars.prob * 98) / 100; q->vars.qdelay = qdelay; q->vars.qlen_old = qlen; /* We restart the measurement cycle if the following conditions are met * 1. If the delay has been low for 2 consecutive Tupdate periods * 2. Calculated drop probability is zero * 3. We have atleast one estimate for the avg_dq_rate ie., * is a non-zero value */ if ((q->vars.qdelay < q->params.target / 2) && (q->vars.qdelay_old < q->params.target / 2) && (q->vars.prob == 0) && (q->vars.avg_dq_rate > 0)) pie_vars_init(&q->vars); } static void pie_timer(unsigned long arg) { struct Qdisc *sch = (struct Qdisc *)arg; struct pie_sched_data *q = qdisc_priv(sch); spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch)); spin_lock(root_lock); calculate_probability(sch); /* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */ if (q->params.tupdate) mod_timer(&q->adapt_timer, jiffies + q->params.tupdate); spin_unlock(root_lock); } static int pie_init(struct Qdisc *sch, struct nlattr *opt) { struct pie_sched_data *q = qdisc_priv(sch); pie_params_init(&q->params); pie_vars_init(&q->vars); sch->limit = q->params.limit; setup_timer(&q->adapt_timer, pie_timer, (unsigned long)sch); if (opt) { int err = pie_change(sch, opt); if (err) return err; } mod_timer(&q->adapt_timer, jiffies + HZ / 2); return 0; } static int pie_dump(struct Qdisc *sch, struct sk_buff *skb) { struct pie_sched_data *q = qdisc_priv(sch); struct nlattr *opts; opts = nla_nest_start(skb, TCA_OPTIONS); if (opts == NULL) goto nla_put_failure; /* convert target from pschedtime to us */ if (nla_put_u32(skb, TCA_PIE_TARGET, ((u32) PSCHED_TICKS2NS(q->params.target)) / NSEC_PER_USEC) || nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) || nla_put_u32(skb, TCA_PIE_TUPDATE, jiffies_to_usecs(q->params.tupdate)) || nla_put_u32(skb, TCA_PIE_ALPHA, q->params.alpha) || nla_put_u32(skb, TCA_PIE_BETA, q->params.beta) || nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) || nla_put_u32(skb, TCA_PIE_BYTEMODE, q->params.bytemode)) goto nla_put_failure; return nla_nest_end(skb, opts); nla_put_failure: nla_nest_cancel(skb, opts); return -1; } static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d) { struct pie_sched_data *q = qdisc_priv(sch); struct tc_pie_xstats st = { .prob = q->vars.prob, .delay = ((u32) PSCHED_TICKS2NS(q->vars.qdelay)) / NSEC_PER_USEC, /* unscale and return dq_rate in bytes per sec */ .avg_dq_rate = q->vars.avg_dq_rate * (PSCHED_TICKS_PER_SEC) >> PIE_SCALE, .packets_in = q->stats.packets_in, .overlimit = q->stats.overlimit, .maxq = q->stats.maxq, .dropped = q->stats.dropped, .ecn_mark = q->stats.ecn_mark, }; return gnet_stats_copy_app(d, &st, sizeof(st)); } static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch) { struct sk_buff *skb; skb = __qdisc_dequeue_head(sch, &sch->q); if (!skb) return NULL; pie_process_dequeue(sch, skb); return skb; } static void pie_reset(struct Qdisc *sch) { struct pie_sched_data *q = qdisc_priv(sch); qdisc_reset_queue(sch); pie_vars_init(&q->vars); } static void pie_destroy(struct Qdisc *sch) { struct pie_sched_data *q = qdisc_priv(sch); q->params.tupdate = 0; del_timer_sync(&q->adapt_timer); } static struct Qdisc_ops pie_qdisc_ops __read_mostly = { .id = "pie", .priv_size = sizeof(struct pie_sched_data), .enqueue = pie_qdisc_enqueue, .dequeue = pie_qdisc_dequeue, .peek = qdisc_peek_dequeued, .init = pie_init, .destroy = pie_destroy, .reset = pie_reset, .change = pie_change, .dump = pie_dump, .dump_stats = pie_dump_stats, .owner = THIS_MODULE, }; static int __init pie_module_init(void) { return register_qdisc(&pie_qdisc_ops); } static void __exit pie_module_exit(void) { unregister_qdisc(&pie_qdisc_ops); } module_init(pie_module_init); module_exit(pie_module_exit); MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler"); MODULE_AUTHOR("Vijay Subramanian"); MODULE_AUTHOR("Mythili Prabhu"); MODULE_LICENSE("GPL");