| /* 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: |
| * RFC 8033: https://tools.ietf.org/html/rfc8033 |
| */ |
| |
| #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 16384 |
| #define DQCOUNT_INVALID -1 |
| #define MAX_PROB 0xffffffffffffffff |
| #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 { |
| u64 prob; /* probability but scaled by u64 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 */ |
| u64 accu_prob; /* accumulated drop probability */ |
| u32 avg_dq_rate; /* bytes per pschedtime tick,scaled */ |
| u32 qlen_old; /* in bytes */ |
| u8 accu_prob_overflows; /* overflows of accu_prob */ |
| }; |
| |
| /* 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; |
| struct Qdisc *sch; |
| }; |
| |
| static void pie_params_init(struct pie_params *params) |
| { |
| params->alpha = 2; |
| params->beta = 20; |
| params->tupdate = usecs_to_jiffies(15 * USEC_PER_MSEC); /* 15 ms */ |
| params->limit = 1000; /* default of 1000 packets */ |
| params->target = PSCHED_NS2TICKS(15 * NSEC_PER_MSEC); /* 15 ms */ |
| params->ecn = false; |
| params->bytemode = false; |
| } |
| |
| static void pie_vars_init(struct pie_vars *vars) |
| { |
| vars->dq_count = DQCOUNT_INVALID; |
| vars->accu_prob = 0; |
| vars->avg_dq_rate = 0; |
| /* default of 150 ms in pschedtime */ |
| vars->burst_time = PSCHED_NS2TICKS(150 * NSEC_PER_MSEC); |
| vars->accu_prob_overflows = 0; |
| } |
| |
| static bool drop_early(struct Qdisc *sch, u32 packet_size) |
| { |
| struct pie_sched_data *q = qdisc_priv(sch); |
| u64 rnd; |
| u64 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 = (u64)packet_size * div_u64(local_prob, mtu); |
| else |
| local_prob = q->vars.prob; |
| |
| if (local_prob == 0) { |
| q->vars.accu_prob = 0; |
| q->vars.accu_prob_overflows = 0; |
| } |
| |
| if (local_prob > MAX_PROB - q->vars.accu_prob) |
| q->vars.accu_prob_overflows++; |
| |
| q->vars.accu_prob += local_prob; |
| |
| if (q->vars.accu_prob_overflows == 0 && |
| q->vars.accu_prob < (MAX_PROB / 100) * 85) |
| return false; |
| if (q->vars.accu_prob_overflows == 8 && |
| q->vars.accu_prob >= MAX_PROB / 2) |
| return true; |
| |
| prandom_bytes(&rnd, 8); |
| if (rnd < local_prob) { |
| q->vars.accu_prob = 0; |
| q->vars.accu_prob_overflows = 0; |
| return true; |
| } |
| |
| return false; |
| } |
| |
| static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch, |
| struct sk_buff **to_free) |
| { |
| 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++; |
| q->vars.accu_prob = 0; |
| q->vars.accu_prob_overflows = 0; |
| return qdisc_drop(skb, sch, to_free); |
| } |
| |
| 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 netlink_ext_ack *extack) |
| { |
| struct pie_sched_data *q = qdisc_priv(sch); |
| struct nlattr *tb[TCA_PIE_MAX + 1]; |
| unsigned int qlen, dropped = 0; |
| int err; |
| |
| if (!opt) |
| return -EINVAL; |
| |
| err = nla_parse_nested(tb, TCA_PIE_MAX, opt, pie_policy, NULL); |
| 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 = __qdisc_dequeue_head(&sch->q); |
| |
| dropped += qdisc_pkt_len(skb); |
| qdisc_qstats_backlog_dec(sch, skb); |
| rtnl_qdisc_drop(skb, sch); |
| } |
| qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped); |
| |
| 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 */ |
| s64 delta = 0; /* determines the change in probability */ |
| u64 oldprob; |
| u64 alpha, beta; |
| u32 power; |
| 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 scaling down |
| * by 16 to come to 0-2 range. |
| */ |
| alpha = ((u64)q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; |
| beta = ((u64)q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; |
| |
| /* We scale alpha and beta differently depending on how heavy the |
| * congestion is. Please see RFC 8033 for details. |
| */ |
| if (q->vars.prob < MAX_PROB / 10) { |
| alpha >>= 1; |
| beta >>= 1; |
| |
| power = 100; |
| while (q->vars.prob < div_u64(MAX_PROB, power) && |
| power <= 1000000) { |
| alpha >>= 2; |
| beta >>= 2; |
| power *= 10; |
| } |
| } |
| |
| /* alpha and beta should be between 0 and 32, in multiples of 1/16 */ |
| delta += alpha * (u64)(qdelay - q->params.target); |
| delta += beta * (u64)(qdelay - qdelay_old); |
| |
| oldprob = q->vars.prob; |
| |
| /* to ensure we increase probability in steps of no more than 2% */ |
| if (delta > (s64)(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) |
| /* Reduce drop probability to 98.4% */ |
| q->vars.prob -= q->vars.prob / 64u; |
| |
| 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(struct timer_list *t) |
| { |
| struct pie_sched_data *q = from_timer(q, t, adapt_timer); |
| struct Qdisc *sch = q->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 netlink_ext_ack *extack) |
| { |
| struct pie_sched_data *q = qdisc_priv(sch); |
| |
| pie_params_init(&q->params); |
| pie_vars_init(&q->vars); |
| sch->limit = q->params.limit; |
| |
| q->sch = sch; |
| timer_setup(&q->adapt_timer, pie_timer, 0); |
| |
| if (opt) { |
| int err = pie_change(sch, opt, extack); |
| |
| 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) |
| 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 = qdisc_dequeue_head(sch); |
| |
| 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"); |