Release 4.7 include/net/codel_impl.h
#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;
}
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static void codel_vars_init(struct codel_vars *vars)
{
memset(vars, 0, sizeof(*vars));
}
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static void codel_stats_init(struct codel_stats *stats)
{
stats->maxpacket = 0;
}
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/*
* 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;
}
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/*
* 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);
}
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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;
}
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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;
}
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#endif
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