linux/include/net/codel.h at master · fabgithub/linux · GitHub

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#ifndef __NET_SCHED_CODEL_H

#define __NET_SCHED_CODEL_H

* Codel - The Controlled-Delay Active Queue Management algorithm

* 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>

#include <linux/reciprocal_div.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;

}

#define codel_time_after(a, b) ((s32)(a) - (s32)(b) > 0)

#define codel_time_after_eq(a, b) ((s32)(a) - (s32)(b) >= 0)

#define codel_time_before(a, b) ((s32)(a) - (s32)(b) < 0)

#define codel_time_before_eq(a, b) ((s32)(a) - (s32)(b) <= 0)

/* 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_divide(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

linux/include/net/codel.h at master · fabgithub/linux · GitHub

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