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C
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/* * 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) 2012,2015 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. * */
/* 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 */
#include <net/inet_ecn.h>
static void codel_params_init(struct codel_params *params){ params->interval = MS2TIME(100); params->target = MS2TIME(5); params->ce_threshold = CODEL_DISABLED_THRESHOLD; params->ce_threshold_mask = 0; params->ce_threshold_selector = 0; 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 = 0;}
/* * 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. * * Clamp the increment to at least 1 tick: a very small interval (or a * large count) can truncate it to zero, stalling the dropping loop. */static codel_time_t codel_control_law(codel_time_t t, codel_time_t interval, u32 rec_inv_sqrt){ return t + max_t(u32, 1, reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT));}
static bool codel_should_drop(const struct sk_buff *skb, void *ctx, struct codel_vars *vars, struct codel_params *params, struct codel_stats *stats, codel_skb_len_t skb_len_func, codel_skb_time_t skb_time_func, u32 *backlog, codel_time_t now){ bool ok_to_drop; u32 skb_len;
if (!skb) { vars->first_above_time = 0; return false; }
skb_len = skb_len_func(skb); WRITE_ONCE(vars->ldelay, now - skb_time_func(skb));
if (unlikely(skb_len > stats->maxpacket)) WRITE_ONCE(stats->maxpacket, skb_len);
if (codel_time_before(vars->ldelay, params->target) || *backlog <= params->mtu) { /* 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;}
static struct sk_buff *codel_dequeue(void *ctx, u32 *backlog, struct codel_params *params, struct codel_vars *vars, struct codel_stats *stats, codel_skb_len_t skb_len_func, codel_skb_time_t skb_time_func, codel_skb_drop_t drop_func, codel_skb_dequeue_t dequeue_func){ struct sk_buff *skb = dequeue_func(vars, ctx); unsigned int drops = 0; codel_time_t now; bool drop;
if (!skb) { vars->first_above_time = 0; WRITE_ONCE(vars->dropping, false); return skb; } now = codel_get_time(); drop = codel_should_drop(skb, ctx, vars, params, stats, skb_len_func, skb_time_func, backlog, now); if (vars->dropping) { if (!drop) { /* sojourn time below target - leave dropping state */ WRITE_ONCE(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)) { if (++drops > CODEL_MAX_DROPS_PER_DEQUEUE) { /* fell far behind the schedule */ WRITE_ONCE(vars->drop_next, codel_control_law(now, params->interval, vars->rec_inv_sqrt)); break; } /* dont care of possible wrap * since there is no more divide. */ WRITE_ONCE(vars->count, vars->count + 1); codel_Newton_step(vars); if (params->ecn && INET_ECN_set_ce(skb)) { WRITE_ONCE(stats->ecn_mark, stats->ecn_mark + 1); WRITE_ONCE(vars->drop_next, codel_control_law(vars->drop_next, params->interval, vars->rec_inv_sqrt)); goto end; } stats->drop_len += skb_len_func(skb); drop_func(skb, ctx); stats->drop_count++; skb = dequeue_func(vars, ctx); if (!codel_should_drop(skb, ctx, vars, params, stats, skb_len_func, skb_time_func, backlog, now)) { /* leave dropping state */ WRITE_ONCE(vars->dropping, false); } else { /* and schedule the next drop */ WRITE_ONCE(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)) { WRITE_ONCE(stats->ecn_mark, stats->ecn_mark + 1); } else { stats->drop_len += skb_len_func(skb); drop_func(skb, ctx); stats->drop_count++;
skb = dequeue_func(vars, ctx); drop = codel_should_drop(skb, ctx, vars, params, stats, skb_len_func, skb_time_func, backlog, now); } WRITE_ONCE(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)) { WRITE_ONCE(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 { WRITE_ONCE(vars->count, 1); vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT; } WRITE_ONCE(vars->lastcount, vars->count); WRITE_ONCE(vars->drop_next, codel_control_law(now, params->interval, vars->rec_inv_sqrt)); }end: if (skb && codel_time_after(vars->ldelay, params->ce_threshold)) { bool set_ce = true;
if (params->ce_threshold_mask) { int dsfield = skb_get_dsfield(skb);
set_ce = (dsfield >= 0 && (((u8)dsfield & params->ce_threshold_mask) == params->ce_threshold_selector)); } if (set_ce && INET_ECN_set_ce(skb)) WRITE_ONCE(stats->ce_mark, stats->ce_mark + 1); } return skb;}
#endif