![Gautam Ramakrishnan](/assets/img/avatar_default.png)
RFC 8033 suggests an alternative approach to calculate the queue delay in PIE by using a timestamp on every enqueued packet. This patch adds an implementation of that approach and sets it as the default method to calculate queue delay. The previous method (based on Little's law) to calculate queue delay is set as optional. Signed-off-by: Gautam Ramakrishnan <gautamramk@gmail.com> Signed-off-by: Leslie Monis <lesliemonis@gmail.com> Signed-off-by: Mohit P. Tahiliani <tahiliani@nitk.edu.in> Acked-by: Dave Taht <dave.taht@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
667 lines
18 KiB
C
667 lines
18 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (C) 2013 Cisco Systems, Inc, 2013.
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*
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* Author: Vijay Subramanian <vijaynsu@cisco.com>
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* Author: Mythili Prabhu <mysuryan@cisco.com>
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*
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* ECN support is added by Naeem Khademi <naeemk@ifi.uio.no>
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* University of Oslo, Norway.
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*
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* References:
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* RFC 8033: https://tools.ietf.org/html/rfc8033
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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 <net/pkt_sched.h>
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#include <net/inet_ecn.h>
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#define QUEUE_THRESHOLD 16384
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#define DQCOUNT_INVALID -1
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#define DTIME_INVALID 0xffffffffffffffff
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#define MAX_PROB 0xffffffffffffffff
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#define PIE_SCALE 8
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/* parameters used */
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struct pie_params {
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psched_time_t target; /* user specified target delay in pschedtime */
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u32 tupdate; /* timer frequency (in jiffies) */
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u32 limit; /* number of packets that can be enqueued */
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u32 alpha; /* alpha and beta are between 0 and 32 */
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u32 beta; /* and are used for shift relative to 1 */
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bool ecn; /* true if ecn is enabled */
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bool bytemode; /* to scale drop early prob based on pkt size */
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u8 dq_rate_estimator; /* to calculate delay using Little's law */
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};
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/* variables used */
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struct pie_vars {
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u64 prob; /* probability but scaled by u64 limit. */
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psched_time_t burst_time;
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psched_time_t qdelay;
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psched_time_t qdelay_old;
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u64 dq_count; /* measured in bytes */
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psched_time_t dq_tstamp; /* drain rate */
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u64 accu_prob; /* accumulated drop probability */
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u32 avg_dq_rate; /* bytes per pschedtime tick,scaled */
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u32 qlen_old; /* in bytes */
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u8 accu_prob_overflows; /* overflows of accu_prob */
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};
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/* statistics gathering */
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struct pie_stats {
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u32 packets_in; /* total number of packets enqueued */
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u32 dropped; /* packets dropped due to pie_action */
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u32 overlimit; /* dropped due to lack of space in queue */
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u32 maxq; /* maximum queue size */
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u32 ecn_mark; /* packets marked with ECN */
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};
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/* private data for the Qdisc */
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struct pie_sched_data {
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struct pie_params params;
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struct pie_vars vars;
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struct pie_stats stats;
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struct timer_list adapt_timer;
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struct Qdisc *sch;
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};
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static void pie_params_init(struct pie_params *params)
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{
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params->alpha = 2;
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params->beta = 20;
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params->tupdate = usecs_to_jiffies(15 * USEC_PER_MSEC); /* 15 ms */
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params->limit = 1000; /* default of 1000 packets */
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params->target = PSCHED_NS2TICKS(15 * NSEC_PER_MSEC); /* 15 ms */
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params->ecn = false;
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params->bytemode = false;
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params->dq_rate_estimator = false;
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}
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/* private skb vars */
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struct pie_skb_cb {
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psched_time_t enqueue_time;
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};
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static struct pie_skb_cb *get_pie_cb(const struct sk_buff *skb)
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{
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qdisc_cb_private_validate(skb, sizeof(struct pie_skb_cb));
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return (struct pie_skb_cb *)qdisc_skb_cb(skb)->data;
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}
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static psched_time_t pie_get_enqueue_time(const struct sk_buff *skb)
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{
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return get_pie_cb(skb)->enqueue_time;
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}
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static void pie_set_enqueue_time(struct sk_buff *skb)
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{
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get_pie_cb(skb)->enqueue_time = psched_get_time();
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}
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static void pie_vars_init(struct pie_vars *vars)
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{
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vars->dq_count = DQCOUNT_INVALID;
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vars->dq_tstamp = DTIME_INVALID;
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vars->accu_prob = 0;
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vars->avg_dq_rate = 0;
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/* default of 150 ms in pschedtime */
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vars->burst_time = PSCHED_NS2TICKS(150 * NSEC_PER_MSEC);
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vars->accu_prob_overflows = 0;
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}
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static bool drop_early(struct Qdisc *sch, u32 packet_size)
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{
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struct pie_sched_data *q = qdisc_priv(sch);
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u64 rnd;
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u64 local_prob = q->vars.prob;
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u32 mtu = psched_mtu(qdisc_dev(sch));
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/* If there is still burst allowance left skip random early drop */
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if (q->vars.burst_time > 0)
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return false;
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/* If current delay is less than half of target, and
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* if drop prob is low already, disable early_drop
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*/
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if ((q->vars.qdelay < q->params.target / 2) &&
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(q->vars.prob < MAX_PROB / 5))
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return false;
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/* If we have fewer than 2 mtu-sized packets, disable drop_early,
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* similar to min_th in RED
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*/
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if (sch->qstats.backlog < 2 * mtu)
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return false;
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/* If bytemode is turned on, use packet size to compute new
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* probablity. Smaller packets will have lower drop prob in this case
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*/
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if (q->params.bytemode && packet_size <= mtu)
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local_prob = (u64)packet_size * div_u64(local_prob, mtu);
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else
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local_prob = q->vars.prob;
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if (local_prob == 0) {
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q->vars.accu_prob = 0;
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q->vars.accu_prob_overflows = 0;
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}
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if (local_prob > MAX_PROB - q->vars.accu_prob)
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q->vars.accu_prob_overflows++;
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q->vars.accu_prob += local_prob;
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if (q->vars.accu_prob_overflows == 0 &&
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q->vars.accu_prob < (MAX_PROB / 100) * 85)
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return false;
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if (q->vars.accu_prob_overflows == 8 &&
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q->vars.accu_prob >= MAX_PROB / 2)
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return true;
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prandom_bytes(&rnd, 8);
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if (rnd < local_prob) {
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q->vars.accu_prob = 0;
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q->vars.accu_prob_overflows = 0;
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return true;
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}
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return false;
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}
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static int pie_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 pie_sched_data *q = qdisc_priv(sch);
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bool enqueue = false;
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if (unlikely(qdisc_qlen(sch) >= sch->limit)) {
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q->stats.overlimit++;
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goto out;
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}
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if (!drop_early(sch, skb->len)) {
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enqueue = true;
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} else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) &&
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INET_ECN_set_ce(skb)) {
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/* If packet is ecn capable, mark it if drop probability
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* is lower than 10%, else drop it.
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*/
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q->stats.ecn_mark++;
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enqueue = true;
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}
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/* we can enqueue the packet */
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if (enqueue) {
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/* Set enqueue time only when dq_rate_estimator is disabled. */
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if (!q->params.dq_rate_estimator)
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pie_set_enqueue_time(skb);
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q->stats.packets_in++;
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if (qdisc_qlen(sch) > q->stats.maxq)
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q->stats.maxq = qdisc_qlen(sch);
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return qdisc_enqueue_tail(skb, sch);
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}
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out:
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q->stats.dropped++;
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q->vars.accu_prob = 0;
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q->vars.accu_prob_overflows = 0;
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return qdisc_drop(skb, sch, to_free);
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}
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static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = {
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[TCA_PIE_TARGET] = {.type = NLA_U32},
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[TCA_PIE_LIMIT] = {.type = NLA_U32},
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[TCA_PIE_TUPDATE] = {.type = NLA_U32},
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[TCA_PIE_ALPHA] = {.type = NLA_U32},
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[TCA_PIE_BETA] = {.type = NLA_U32},
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[TCA_PIE_ECN] = {.type = NLA_U32},
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[TCA_PIE_BYTEMODE] = {.type = NLA_U32},
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[TCA_PIE_DQ_RATE_ESTIMATOR] = {.type = NLA_U32},
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};
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static int pie_change(struct Qdisc *sch, struct nlattr *opt,
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struct netlink_ext_ack *extack)
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{
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struct pie_sched_data *q = qdisc_priv(sch);
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struct nlattr *tb[TCA_PIE_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_deprecated(tb, TCA_PIE_MAX, opt, pie_policy,
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NULL);
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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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/* convert from microseconds to pschedtime */
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if (tb[TCA_PIE_TARGET]) {
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/* target is in us */
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u32 target = nla_get_u32(tb[TCA_PIE_TARGET]);
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/* convert to pschedtime */
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q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC);
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}
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/* tupdate is in jiffies */
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if (tb[TCA_PIE_TUPDATE])
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q->params.tupdate =
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usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE]));
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if (tb[TCA_PIE_LIMIT]) {
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u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]);
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q->params.limit = limit;
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sch->limit = limit;
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}
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if (tb[TCA_PIE_ALPHA])
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q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]);
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if (tb[TCA_PIE_BETA])
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q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]);
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if (tb[TCA_PIE_ECN])
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q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]);
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if (tb[TCA_PIE_BYTEMODE])
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q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]);
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if (tb[TCA_PIE_DQ_RATE_ESTIMATOR])
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q->params.dq_rate_estimator =
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nla_get_u32(tb[TCA_PIE_DQ_RATE_ESTIMATOR]);
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/* Drop excess packets if new limit is lower */
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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 = __qdisc_dequeue_head(&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 void pie_process_dequeue(struct Qdisc *sch, struct sk_buff *skb)
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{
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struct pie_sched_data *q = qdisc_priv(sch);
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int qlen = sch->qstats.backlog; /* current queue size in bytes */
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psched_time_t now = psched_get_time();
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u32 dtime = 0;
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/* If dq_rate_estimator is disabled, calculate qdelay using the
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* packet timestamp.
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*/
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if (!q->params.dq_rate_estimator) {
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q->vars.qdelay = now - pie_get_enqueue_time(skb);
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if (q->vars.dq_tstamp != DTIME_INVALID)
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dtime = now - q->vars.dq_tstamp;
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q->vars.dq_tstamp = now;
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if (qlen == 0)
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q->vars.qdelay = 0;
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if (dtime == 0)
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return;
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goto burst_allowance_reduction;
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}
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/* If current queue is about 10 packets or more and dq_count is unset
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* we have enough packets to calculate the drain rate. Save
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* current time as dq_tstamp and start measurement cycle.
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*/
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if (qlen >= QUEUE_THRESHOLD && q->vars.dq_count == DQCOUNT_INVALID) {
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q->vars.dq_tstamp = psched_get_time();
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q->vars.dq_count = 0;
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}
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/* Calculate the average drain rate from this value. If queue length
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* has receded to a small value viz., <= QUEUE_THRESHOLD bytes,reset
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* the dq_count to -1 as we don't have enough packets to calculate the
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* drain rate anymore The following if block is entered only when we
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* have a substantial queue built up (QUEUE_THRESHOLD bytes or more)
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* and we calculate the drain rate for the threshold here. dq_count is
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* in bytes, time difference in psched_time, hence rate is in
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* bytes/psched_time.
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*/
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if (q->vars.dq_count != DQCOUNT_INVALID) {
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q->vars.dq_count += skb->len;
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if (q->vars.dq_count >= QUEUE_THRESHOLD) {
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u32 count = q->vars.dq_count << PIE_SCALE;
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dtime = now - q->vars.dq_tstamp;
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if (dtime == 0)
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return;
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count = count / dtime;
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if (q->vars.avg_dq_rate == 0)
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q->vars.avg_dq_rate = count;
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else
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q->vars.avg_dq_rate =
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(q->vars.avg_dq_rate -
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(q->vars.avg_dq_rate >> 3)) + (count >> 3);
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/* If the queue has receded below the threshold, we hold
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* on to the last drain rate calculated, else we reset
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* dq_count to 0 to re-enter the if block when the next
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* packet is dequeued
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*/
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if (qlen < QUEUE_THRESHOLD) {
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q->vars.dq_count = DQCOUNT_INVALID;
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} else {
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q->vars.dq_count = 0;
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q->vars.dq_tstamp = psched_get_time();
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}
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goto burst_allowance_reduction;
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}
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}
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return;
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burst_allowance_reduction:
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if (q->vars.burst_time > 0) {
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if (q->vars.burst_time > dtime)
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q->vars.burst_time -= dtime;
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else
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q->vars.burst_time = 0;
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}
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}
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static void calculate_probability(struct Qdisc *sch)
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{
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struct pie_sched_data *q = qdisc_priv(sch);
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u32 qlen = sch->qstats.backlog; /* queue size in bytes */
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psched_time_t qdelay = 0; /* in pschedtime */
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psched_time_t qdelay_old = 0; /* in pschedtime */
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s64 delta = 0; /* determines the change in probability */
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u64 oldprob;
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u64 alpha, beta;
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u32 power;
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bool update_prob = true;
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if (q->params.dq_rate_estimator) {
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qdelay_old = q->vars.qdelay;
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q->vars.qdelay_old = q->vars.qdelay;
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if (q->vars.avg_dq_rate > 0)
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qdelay = (qlen << PIE_SCALE) / q->vars.avg_dq_rate;
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else
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qdelay = 0;
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} else {
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qdelay = q->vars.qdelay;
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qdelay_old = q->vars.qdelay_old;
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}
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/* If qdelay is zero and qlen is not, it means qlen is very small, less
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* than dequeue_rate, so we do not update probabilty in this round
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*/
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if (qdelay == 0 && qlen != 0)
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update_prob = false;
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/* In the algorithm, alpha and beta are between 0 and 2 with typical
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* value for alpha as 0.125. In this implementation, we use values 0-32
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* passed from user space to represent this. Also, alpha and beta have
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* unit of HZ and need to be scaled before they can used to update
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* probability. alpha/beta are updated locally below by scaling down
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* by 16 to come to 0-2 range.
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*/
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alpha = ((u64)q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
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beta = ((u64)q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
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/* We scale alpha and beta differently depending on how heavy the
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* congestion is. Please see RFC 8033 for details.
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*/
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if (q->vars.prob < MAX_PROB / 10) {
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alpha >>= 1;
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beta >>= 1;
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power = 100;
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while (q->vars.prob < div_u64(MAX_PROB, power) &&
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power <= 1000000) {
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alpha >>= 2;
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beta >>= 2;
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power *= 10;
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}
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}
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/* alpha and beta should be between 0 and 32, in multiples of 1/16 */
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delta += alpha * (u64)(qdelay - q->params.target);
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delta += beta * (u64)(qdelay - qdelay_old);
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oldprob = q->vars.prob;
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/* to ensure we increase probability in steps of no more than 2% */
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if (delta > (s64)(MAX_PROB / (100 / 2)) &&
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q->vars.prob >= MAX_PROB / 10)
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delta = (MAX_PROB / 100) * 2;
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/* Non-linear drop:
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* Tune drop probability to increase quickly for high delays(>= 250ms)
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* 250ms is derived through experiments and provides error protection
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*/
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if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC)))
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delta += MAX_PROB / (100 / 2);
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q->vars.prob += delta;
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if (delta > 0) {
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/* prevent overflow */
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if (q->vars.prob < oldprob) {
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q->vars.prob = MAX_PROB;
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/* 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. If average dq_rate_estimator is enabled, 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->params.dq_rate_estimator || q->vars.avg_dq_rate > 0)) {
|
|
pie_vars_init(&q->vars);
|
|
}
|
|
|
|
if (!q->params.dq_rate_estimator)
|
|
q->vars.qdelay_old = qdelay;
|
|
}
|
|
|
|
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_noflag(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) ||
|
|
nla_put_u32(skb, TCA_PIE_DQ_RATE_ESTIMATOR,
|
|
q->params.dq_rate_estimator))
|
|
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,
|
|
.packets_in = q->stats.packets_in,
|
|
.overlimit = q->stats.overlimit,
|
|
.maxq = q->stats.maxq,
|
|
.dropped = q->stats.dropped,
|
|
.ecn_mark = q->stats.ecn_mark,
|
|
};
|
|
|
|
/* avg_dq_rate is only valid if dq_rate_estimator is enabled */
|
|
st.dq_rate_estimating = q->params.dq_rate_estimator;
|
|
|
|
/* unscale and return dq_rate in bytes per sec */
|
|
if (q->params.dq_rate_estimator)
|
|
st.avg_dq_rate = q->vars.avg_dq_rate *
|
|
(PSCHED_TICKS_PER_SEC) >> PIE_SCALE;
|
|
|
|
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");
|