343 строки
10 KiB
C
343 строки
10 KiB
C
#ifndef __NET_SCHED_CODEL_H
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#define __NET_SCHED_CODEL_H
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/*
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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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* Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net>
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* Copyright (C) 2012 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/types.h>
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#include <linux/ktime.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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#include <linux/reciprocal_div.h>
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/* Controlling Queue Delay (CoDel) algorithm
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* =========================================
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* Source : Kathleen Nichols and Van Jacobson
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* http://queue.acm.org/detail.cfm?id=2209336
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*
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* Implemented on linux by Dave Taht and Eric Dumazet
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*/
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/* CoDel uses a 1024 nsec clock, encoded in u32
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* This gives a range of 2199 seconds, because of signed compares
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*/
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typedef u32 codel_time_t;
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typedef s32 codel_tdiff_t;
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#define CODEL_SHIFT 10
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#define MS2TIME(a) ((a * NSEC_PER_MSEC) >> CODEL_SHIFT)
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static inline codel_time_t codel_get_time(void)
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{
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u64 ns = ktime_to_ns(ktime_get());
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return ns >> CODEL_SHIFT;
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}
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#define codel_time_after(a, b) ((s32)(a) - (s32)(b) > 0)
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#define codel_time_after_eq(a, b) ((s32)(a) - (s32)(b) >= 0)
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#define codel_time_before(a, b) ((s32)(a) - (s32)(b) < 0)
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#define codel_time_before_eq(a, b) ((s32)(a) - (s32)(b) <= 0)
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/* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
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struct codel_skb_cb {
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codel_time_t enqueue_time;
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};
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static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
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{
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qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb));
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return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data;
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}
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static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
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{
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return get_codel_cb(skb)->enqueue_time;
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}
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static void codel_set_enqueue_time(struct sk_buff *skb)
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{
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get_codel_cb(skb)->enqueue_time = codel_get_time();
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}
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static inline u32 codel_time_to_us(codel_time_t val)
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{
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u64 valns = ((u64)val << CODEL_SHIFT);
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do_div(valns, NSEC_PER_USEC);
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return (u32)valns;
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}
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/**
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* struct codel_params - contains codel parameters
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* @target: target queue size (in time units)
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* @interval: width of moving time window
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* @ecn: is Explicit Congestion Notification enabled
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*/
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struct codel_params {
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codel_time_t target;
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codel_time_t interval;
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bool ecn;
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};
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/**
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* struct codel_vars - contains codel variables
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* @count: how many drops we've done since the last time we
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* entered dropping state
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* @lastcount: count at entry to dropping state
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* @dropping: set to true if in dropping state
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* @rec_inv_sqrt: reciprocal value of sqrt(count) >> 1
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* @first_above_time: when we went (or will go) continuously above target
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* for interval
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* @drop_next: time to drop next packet, or when we dropped last
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* @ldelay: sojourn time of last dequeued packet
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*/
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struct codel_vars {
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u32 count;
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u32 lastcount;
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bool dropping;
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u16 rec_inv_sqrt;
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codel_time_t first_above_time;
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codel_time_t drop_next;
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codel_time_t ldelay;
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};
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#define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */
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/* needed shift to get a Q0.32 number from rec_inv_sqrt */
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#define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS)
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/**
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* struct codel_stats - contains codel shared variables and stats
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* @maxpacket: largest packet we've seen so far
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* @drop_count: temp count of dropped packets in dequeue()
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* ecn_mark: number of packets we ECN marked instead of dropping
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*/
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struct codel_stats {
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u32 maxpacket;
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u32 drop_count;
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u32 ecn_mark;
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};
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static void codel_params_init(struct codel_params *params)
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{
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params->interval = MS2TIME(100);
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params->target = MS2TIME(5);
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params->ecn = false;
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}
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static void codel_vars_init(struct codel_vars *vars)
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{
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memset(vars, 0, sizeof(*vars));
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}
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static void codel_stats_init(struct codel_stats *stats)
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{
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stats->maxpacket = 256;
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}
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/*
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* http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
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* new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
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*
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* Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
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*/
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static void codel_Newton_step(struct codel_vars *vars)
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{
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u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
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u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
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u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
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val >>= 2; /* avoid overflow in following multiply */
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val = (val * invsqrt) >> (32 - 2 + 1);
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vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
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}
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/*
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* CoDel control_law is t + interval/sqrt(count)
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* We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
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* both sqrt() and divide operation.
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*/
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static codel_time_t codel_control_law(codel_time_t t,
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codel_time_t interval,
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u32 rec_inv_sqrt)
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{
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return t + reciprocal_divide(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
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}
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static bool codel_should_drop(const struct sk_buff *skb,
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struct Qdisc *sch,
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struct codel_vars *vars,
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struct codel_params *params,
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struct codel_stats *stats,
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codel_time_t now)
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{
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bool ok_to_drop;
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if (!skb) {
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vars->first_above_time = 0;
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return false;
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}
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vars->ldelay = now - codel_get_enqueue_time(skb);
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sch->qstats.backlog -= qdisc_pkt_len(skb);
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if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket))
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stats->maxpacket = qdisc_pkt_len(skb);
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if (codel_time_before(vars->ldelay, params->target) ||
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sch->qstats.backlog <= stats->maxpacket) {
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/* went below - stay below for at least interval */
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vars->first_above_time = 0;
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return false;
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}
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ok_to_drop = false;
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if (vars->first_above_time == 0) {
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/* just went above from below. If we stay above
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* for at least interval we'll say it's ok to drop
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*/
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vars->first_above_time = now + params->interval;
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} else if (codel_time_after(now, vars->first_above_time)) {
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ok_to_drop = true;
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}
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return ok_to_drop;
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}
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typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
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struct Qdisc *sch);
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static struct sk_buff *codel_dequeue(struct Qdisc *sch,
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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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codel_skb_dequeue_t dequeue_func)
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{
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struct sk_buff *skb = dequeue_func(vars, sch);
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codel_time_t now;
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bool drop;
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if (!skb) {
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vars->dropping = false;
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return skb;
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}
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now = codel_get_time();
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drop = codel_should_drop(skb, sch, vars, params, stats, now);
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if (vars->dropping) {
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if (!drop) {
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/* sojourn time below target - leave dropping state */
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vars->dropping = false;
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} else if (codel_time_after_eq(now, vars->drop_next)) {
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/* It's time for the next drop. Drop the current
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* packet and dequeue the next. The dequeue might
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* take us out of dropping state.
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* If not, schedule the next drop.
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* A large backlog might result in drop rates so high
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* that the next drop should happen now,
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* hence the while loop.
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*/
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while (vars->dropping &&
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codel_time_after_eq(now, vars->drop_next)) {
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vars->count++; /* dont care of possible wrap
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* since there is no more divide
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*/
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codel_Newton_step(vars);
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if (params->ecn && INET_ECN_set_ce(skb)) {
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stats->ecn_mark++;
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vars->drop_next =
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codel_control_law(vars->drop_next,
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params->interval,
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vars->rec_inv_sqrt);
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goto end;
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}
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qdisc_drop(skb, sch);
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stats->drop_count++;
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skb = dequeue_func(vars, sch);
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if (!codel_should_drop(skb, sch,
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vars, params, stats, now)) {
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/* leave dropping state */
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vars->dropping = false;
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} else {
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/* and schedule the next drop */
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vars->drop_next =
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codel_control_law(vars->drop_next,
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params->interval,
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vars->rec_inv_sqrt);
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}
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}
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}
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} else if (drop) {
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if (params->ecn && INET_ECN_set_ce(skb)) {
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stats->ecn_mark++;
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} else {
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qdisc_drop(skb, sch);
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stats->drop_count++;
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skb = dequeue_func(vars, sch);
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drop = codel_should_drop(skb, sch, vars, params,
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stats, now);
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}
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vars->dropping = true;
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/* if min went above target close to when we last went below it
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* assume that the drop rate that controlled the queue on the
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* last cycle is a good starting point to control it now.
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*/
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if (codel_time_before(now - vars->drop_next,
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16 * params->interval)) {
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vars->count = (vars->count - vars->lastcount) | 1;
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/* we dont care if rec_inv_sqrt approximation
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* is not very precise :
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* Next Newton steps will correct it quadratically.
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*/
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codel_Newton_step(vars);
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} else {
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vars->count = 1;
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vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
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}
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vars->lastcount = vars->count;
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vars->drop_next = codel_control_law(now, params->interval,
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vars->rec_inv_sqrt);
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}
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end:
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return skb;
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}
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#endif
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