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-rw-r--r--include/net/codel.h355
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diff --git a/include/net/codel.h b/include/net/codel.h
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+#ifndef __NET_SCHED_CODEL_H
+#define __NET_SCHED_CODEL_H
+
+/*
+ * Codel - The Controlled-Delay Active Queue Management algorithm
+ *
+ * Copyright (C) 2011-2012 Kathleen Nichols <nichols@pollere.com>
+ * Copyright (C) 2011-2012 Van Jacobson <van@pollere.net>
+ * Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net>
+ * Copyright (C) 2012 Eric Dumazet <edumazet@google.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions, and the following disclaimer,
+ * without modification.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * 3. The names of the authors may not be used to endorse or promote products
+ * derived from this software without specific prior written permission.
+ *
+ * Alternatively, provided that this notice is retained in full, this
+ * software may be distributed under the terms of the GNU General
+ * Public License ("GPL") version 2, in which case the provisions of the
+ * GPL apply INSTEAD OF those given above.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ */
+
+#include <linux/types.h>
+#include <linux/ktime.h>
+#include <linux/skbuff.h>
+#include <net/pkt_sched.h>
+#include <net/inet_ecn.h>
+
+/* Controlling Queue Delay (CoDel) algorithm
+ * =========================================
+ * Source : Kathleen Nichols and Van Jacobson
+ * http://queue.acm.org/detail.cfm?id=2209336
+ *
+ * Implemented on linux by Dave Taht and Eric Dumazet
+ */
+
+
+/* CoDel uses a 1024 nsec clock, encoded in u32
+ * This gives a range of 2199 seconds, because of signed compares
+ */
+typedef u32 codel_time_t;
+typedef s32 codel_tdiff_t;
+#define CODEL_SHIFT 10
+#define MS2TIME(a) ((a * NSEC_PER_MSEC) >> CODEL_SHIFT)
+
+static inline codel_time_t codel_get_time(void)
+{
+ u64 ns = ktime_to_ns(ktime_get());
+
+ return ns >> CODEL_SHIFT;
+}
+
+/* Dealing with timer wrapping, according to RFC 1982, as desc in wikipedia:
+ * https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
+ * codel_time_after(a,b) returns true if the time a is after time b.
+ */
+#define codel_time_after(a, b) \
+ (typecheck(codel_time_t, a) && \
+ typecheck(codel_time_t, b) && \
+ ((s32)((a) - (b)) > 0))
+#define codel_time_before(a, b) codel_time_after(b, a)
+
+#define codel_time_after_eq(a, b) \
+ (typecheck(codel_time_t, a) && \
+ typecheck(codel_time_t, b) && \
+ ((s32)((a) - (b)) >= 0))
+#define codel_time_before_eq(a, b) codel_time_after_eq(b, a)
+
+/* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
+struct codel_skb_cb {
+ codel_time_t enqueue_time;
+};
+
+static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
+{
+ qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb));
+ return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data;
+}
+
+static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
+{
+ return get_codel_cb(skb)->enqueue_time;
+}
+
+static void codel_set_enqueue_time(struct sk_buff *skb)
+{
+ get_codel_cb(skb)->enqueue_time = codel_get_time();
+}
+
+static inline u32 codel_time_to_us(codel_time_t val)
+{
+ u64 valns = ((u64)val << CODEL_SHIFT);
+
+ do_div(valns, NSEC_PER_USEC);
+ return (u32)valns;
+}
+
+/**
+ * struct codel_params - contains codel parameters
+ * @target: target queue size (in time units)
+ * @interval: width of moving time window
+ * @ecn: is Explicit Congestion Notification enabled
+ */
+struct codel_params {
+ codel_time_t target;
+ codel_time_t interval;
+ bool ecn;
+};
+
+/**
+ * struct codel_vars - contains codel variables
+ * @count: how many drops we've done since the last time we
+ * entered dropping state
+ * @lastcount: count at entry to dropping state
+ * @dropping: set to true if in dropping state
+ * @rec_inv_sqrt: reciprocal value of sqrt(count) >> 1
+ * @first_above_time: when we went (or will go) continuously above target
+ * for interval
+ * @drop_next: time to drop next packet, or when we dropped last
+ * @ldelay: sojourn time of last dequeued packet
+ */
+struct codel_vars {
+ u32 count;
+ u32 lastcount;
+ bool dropping;
+ u16 rec_inv_sqrt;
+ codel_time_t first_above_time;
+ codel_time_t drop_next;
+ codel_time_t ldelay;
+};
+
+#define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */
+/* needed shift to get a Q0.32 number from rec_inv_sqrt */
+#define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS)
+
+/**
+ * struct codel_stats - contains codel shared variables and stats
+ * @maxpacket: largest packet we've seen so far
+ * @drop_count: temp count of dropped packets in dequeue()
+ * ecn_mark: number of packets we ECN marked instead of dropping
+ */
+struct codel_stats {
+ u32 maxpacket;
+ u32 drop_count;
+ u32 ecn_mark;
+};
+
+static void codel_params_init(struct codel_params *params)
+{
+ params->interval = MS2TIME(100);
+ params->target = MS2TIME(5);
+ params->ecn = false;
+}
+
+static void codel_vars_init(struct codel_vars *vars)
+{
+ memset(vars, 0, sizeof(*vars));
+}
+
+static void codel_stats_init(struct codel_stats *stats)
+{
+ stats->maxpacket = 256;
+}
+
+/*
+ * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
+ * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
+ *
+ * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
+ */
+static void codel_Newton_step(struct codel_vars *vars)
+{
+ u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
+ u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
+ u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
+
+ val >>= 2; /* avoid overflow in following multiply */
+ val = (val * invsqrt) >> (32 - 2 + 1);
+
+ vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
+}
+
+/*
+ * CoDel control_law is t + interval/sqrt(count)
+ * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
+ * both sqrt() and divide operation.
+ */
+static codel_time_t codel_control_law(codel_time_t t,
+ codel_time_t interval,
+ u32 rec_inv_sqrt)
+{
+ return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
+}
+
+static bool codel_should_drop(const struct sk_buff *skb,
+ struct Qdisc *sch,
+ struct codel_vars *vars,
+ struct codel_params *params,
+ struct codel_stats *stats,
+ codel_time_t now)
+{
+ bool ok_to_drop;
+
+ if (!skb) {
+ vars->first_above_time = 0;
+ return false;
+ }
+
+ vars->ldelay = now - codel_get_enqueue_time(skb);
+ sch->qstats.backlog -= qdisc_pkt_len(skb);
+
+ if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket))
+ stats->maxpacket = qdisc_pkt_len(skb);
+
+ if (codel_time_before(vars->ldelay, params->target) ||
+ sch->qstats.backlog <= stats->maxpacket) {
+ /* went below - stay below for at least interval */
+ vars->first_above_time = 0;
+ return false;
+ }
+ ok_to_drop = false;
+ if (vars->first_above_time == 0) {
+ /* just went above from below. If we stay above
+ * for at least interval we'll say it's ok to drop
+ */
+ vars->first_above_time = now + params->interval;
+ } else if (codel_time_after(now, vars->first_above_time)) {
+ ok_to_drop = true;
+ }
+ return ok_to_drop;
+}
+
+typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
+ struct Qdisc *sch);
+
+static struct sk_buff *codel_dequeue(struct Qdisc *sch,
+ struct codel_params *params,
+ struct codel_vars *vars,
+ struct codel_stats *stats,
+ codel_skb_dequeue_t dequeue_func)
+{
+ struct sk_buff *skb = dequeue_func(vars, sch);
+ codel_time_t now;
+ bool drop;
+
+ if (!skb) {
+ vars->dropping = false;
+ return skb;
+ }
+ now = codel_get_time();
+ drop = codel_should_drop(skb, sch, vars, params, stats, now);
+ if (vars->dropping) {
+ if (!drop) {
+ /* sojourn time below target - leave dropping state */
+ vars->dropping = false;
+ } else if (codel_time_after_eq(now, vars->drop_next)) {
+ /* It's time for the next drop. Drop the current
+ * packet and dequeue the next. The dequeue might
+ * take us out of dropping state.
+ * If not, schedule the next drop.
+ * A large backlog might result in drop rates so high
+ * that the next drop should happen now,
+ * hence the while loop.
+ */
+ while (vars->dropping &&
+ codel_time_after_eq(now, vars->drop_next)) {
+ vars->count++; /* dont care of possible wrap
+ * since there is no more divide
+ */
+ codel_Newton_step(vars);
+ if (params->ecn && INET_ECN_set_ce(skb)) {
+ stats->ecn_mark++;
+ vars->drop_next =
+ codel_control_law(vars->drop_next,
+ params->interval,
+ vars->rec_inv_sqrt);
+ goto end;
+ }
+ qdisc_drop(skb, sch);
+ stats->drop_count++;
+ skb = dequeue_func(vars, sch);
+ if (!codel_should_drop(skb, sch,
+ vars, params, stats, now)) {
+ /* leave dropping state */
+ vars->dropping = false;
+ } else {
+ /* and schedule the next drop */
+ vars->drop_next =
+ codel_control_law(vars->drop_next,
+ params->interval,
+ vars->rec_inv_sqrt);
+ }
+ }
+ }
+ } else if (drop) {
+ u32 delta;
+
+ if (params->ecn && INET_ECN_set_ce(skb)) {
+ stats->ecn_mark++;
+ } else {
+ qdisc_drop(skb, sch);
+ stats->drop_count++;
+
+ skb = dequeue_func(vars, sch);
+ drop = codel_should_drop(skb, sch, vars, params,
+ stats, now);
+ }
+ vars->dropping = true;
+ /* if min went above target close to when we last went below it
+ * assume that the drop rate that controlled the queue on the
+ * last cycle is a good starting point to control it now.
+ */
+ delta = vars->count - vars->lastcount;
+ if (delta > 1 &&
+ codel_time_before(now - vars->drop_next,
+ 16 * params->interval)) {
+ vars->count = delta;
+ /* we dont care if rec_inv_sqrt approximation
+ * is not very precise :
+ * Next Newton steps will correct it quadratically.
+ */
+ codel_Newton_step(vars);
+ } else {
+ vars->count = 1;
+ vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
+ }
+ vars->lastcount = vars->count;
+ vars->drop_next = codel_control_law(now, params->interval,
+ vars->rec_inv_sqrt);
+ }
+end:
+ return skb;
+}
+#endif
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