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Diffstat (limited to '')
| -rw-r--r-- | include/net/codel_impl.h | 255 |
1 files changed, 255 insertions, 0 deletions
diff --git a/include/net/codel_impl.h b/include/net/codel_impl.h new file mode 100644 index 000000000..d289b91dc --- /dev/null +++ b/include/net/codel_impl.h @@ -0,0 +1,255 @@ +#ifndef __NET_SCHED_CODEL_IMPL_H +#define __NET_SCHED_CODEL_IMPL_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) 2012,2015 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 + */ + +static void codel_params_init(struct codel_params *params) +{ + params->interval = MS2TIME(100); + params->target = MS2TIME(5); + params->ce_threshold = CODEL_DISABLED_THRESHOLD; + 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. + */ +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, + 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); + vars->ldelay = now - skb_time_func(skb); + + if (unlikely(skb_len > stats->maxpacket)) + 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); + codel_time_t now; + bool drop; + + if (!skb) { + 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 */ + 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; + } + 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 */ + 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 { + 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); + } + 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: + if (skb && codel_time_after(vars->ldelay, params->ce_threshold) && + INET_ECN_set_ce(skb)) + stats->ce_mark++; + return skb; +} + +#endif |