dn_aqm_codel.h

/*
 * Codel - The Controlled-Delay Active Queue Management algorithm.
 * 
 * Copyright (C) 2016 Centre for Advanced Internet Architectures,
 *  Swinburne University of Technology, Melbourne, Australia.
 * Portions of this code were made possible in part by a gift from 
 *  The Comcast Innovation Fund.
 * Implemented by Rasool Al-Saadi <[email protected]>
 * 
 * Copyright (C) 2011-2014 Kathleen Nichols <[email protected]>.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * o  Redistributions of source code must retain the above copyright
 *  notice, this list of conditions, and the following disclaimer,
 *  without modification.
 *
 * o  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.
 * 
 * o  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.
 */

#ifndef _IP_DN_AQM_CODEL_H
#define _IP_DN_AQM_CODEL_H

// XXX How to choose MTAG?
#define FIX_POINT_BITS 16 

enum {
	CODEL_ECN_ENABLED = 1
};

/* Codel parameters */
struct dn_aqm_codel_parms {
	aqm_time_t	target;
	aqm_time_t	interval;
	uint32_t	flags;
};

/* codel status variables */
struct codel_status {
	uint32_t	count;	/* number of dropped pkts since entering drop state */
	uint16_t	dropping;	/* dropping state */
	aqm_time_t	drop_next_time;	/* time for next drop */
	aqm_time_t	first_above_time;	/* time for first ts over target we observed */
	uint16_t	isqrt;	/* last isqrt for control low */
	uint16_t	maxpkt_size;	/* max packet size seen so far */
};

struct mbuf *codel_extract_head(struct dn_queue *, aqm_time_t *);
aqm_time_t control_law(struct codel_status *,
	struct dn_aqm_codel_parms *, aqm_time_t );

__inline static struct mbuf *
codel_dodequeue(struct dn_queue *q, aqm_time_t now, uint16_t *ok_to_drop)
{
	struct mbuf * m;
	struct dn_aqm_codel_parms *cprms;
	struct codel_status *cst;
	aqm_time_t  pkt_ts, sojourn_time;

	*ok_to_drop = 0;
	m = codel_extract_head(q, &pkt_ts);

	cst = q->aqm_status;

	if (m == NULL) {
		/* queue is empty - we can't be above target */
		cst->first_above_time= 0;
		return m;
	}

	cprms = q->fs->aqmcfg;

	/* To span a large range of bandwidths, CoDel runs two
	 * different AQMs in parallel. One is sojourn-time-based
	 * and takes effect when the time to send an MTU-sized
	 * packet is less than target.  The 1st term of the "if"
	 * below does this.  The other is backlog-based and takes
	 * effect when the time to send an MTU-sized packet is >=
	* target. The goal here is to keep the output link
	* utilization high by never allowing the queue to get
	* smaller than the amount that arrives in a typical
	 * interarrival time (MTU-sized packets arriving spaced
	 * by the amount of time it takes to send such a packet on
	 * the bottleneck). The 2nd term of the "if" does this.
	 */
	sojourn_time = now - pkt_ts;
	if (sojourn_time < cprms->target || q->ni.len_bytes <= cst->maxpkt_size) {
		/* went below - stay below for at least interval */
		cst->first_above_time = 0;
	} else {
		if (cst->first_above_time == 0) {
			/* just went above from below. if still above at
			 * first_above_time, will say it's ok to drop. */
			cst->first_above_time = now + cprms->interval;
		} else if (now >= cst->first_above_time) {
			*ok_to_drop = 1;
		}
	}
	return m;
}

/* 
 * Dequeue a packet from queue 'q'
 */
__inline static struct mbuf * 
codel_dequeue(struct dn_queue *q)
{
	struct mbuf *m;
	struct dn_aqm_codel_parms *cprms;
	struct codel_status *cst;
	aqm_time_t now;
	uint16_t ok_to_drop;

	cst = q->aqm_status;
	cprms = q->fs->aqmcfg;
	now = AQM_UNOW;

	m = codel_dodequeue(q, now, &ok_to_drop);
	if (cst->dropping) {
		if (!ok_to_drop) {
			/* sojourn time below target - leave dropping state */
			cst->dropping = false;
		}
		/*
		 * Time for the next drop. Drop current packet and dequeue
		 * next.  If the dequeue doesn't take us out of dropping
		 * state, 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 (now >= cst->drop_next_time && cst->dropping) {
			/* mark the packet */
			if (cprms->flags & CODEL_ECN_ENABLED && ecn_mark(m)) {
				cst->count++;
				/* schedule the next mark. */
				cst->drop_next_time = control_law(cst, cprms,
					cst->drop_next_time);
				return m;
			}

			/* drop the packet */
			update_stats(q, 0, 1);
			FREE_PKT(m);
			m = codel_dodequeue(q, now, &ok_to_drop);

			if (!ok_to_drop) {
				/* leave dropping state */
				cst->dropping = false;
			} else {
				cst->count++;
				/* schedule the next drop. */
				cst->drop_next_time = control_law(cst, cprms,
					cst->drop_next_time);
			}
		}
	/* If we get here we're not in dropping state. The 'ok_to_drop'
	 * return from dodequeue means that the sojourn time has been
	 * above 'target' for 'interval' so enter dropping state.
	 */
	} else if (ok_to_drop) {
		/* if ECN option is disabled or the packet cannot be marked,
		 * drop the packet and extract another.
		 */
		if (!(cprms->flags & CODEL_ECN_ENABLED) || !ecn_mark(m)) {
			update_stats(q, 0, 1);
			FREE_PKT(m);
			m = codel_dodequeue(q, now, &ok_to_drop);
		}

		cst->dropping = true;

		/* If min went above target close to when it last went
		 * below, assume that the drop rate that controlled the
		 * queue on the last cycle is a good starting point to
		 * control it now. ('drop_next' will be at most 'interval'
		 * later than the time of the last drop so 'now - drop_next'
		 * is a good approximation of the time from the last drop
		 * until now.)
		 */
		cst->count = (cst->count > 2 && ((aqm_stime_t)now - 
			(aqm_stime_t)cst->drop_next_time) < 8* cprms->interval)?
				cst->count - 2 : 1;
		/* we don't have to set initial guess for Newton's method isqrt as
		 * we initilaize  isqrt in control_law function when count == 1 */
		cst->drop_next_time = control_law(cst, cprms, now);
	}

	return m;
}

#endif