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Commit 8af2a218 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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sch_red: Adaptative RED AQM 

Adaptative RED AQM for linux, based on paper from Sally FLoyd,
Ramakrishna Gummadi, and Scott Shenker, August 2001 :

http://icir.org/floyd/papers/adaptiveRed.pdf



Goal of Adaptative RED is to make max_p a dynamic value between 1% and
50% to reach the target average queue : (max_th - min_th) / 2

Every 500 ms:
 if (avg > target and max_p <= 0.5)
  increase max_p : max_p += alpha;
 else if (avg < target and max_p >= 0.01)
  decrease max_p : max_p *= beta;

target :[min_th + 0.4*(min_th - max_th),
          min_th + 0.6*(min_th - max_th)].
alpha : min(0.01, max_p / 4)
beta : 0.9
max_P is a Q0.32 fixed point number (unsigned, with 32 bits mantissa)

Changes against our RED implementation are :

max_p is no longer a negative power of two (1/(2^Plog)), but a Q0.32
fixed point number, to allow full range described in Adatative paper.

To deliver a random number, we now use a reciprocal divide (thats really
a multiply), but this operation is done once per marked/droped packet
when in RED_BETWEEN_TRESH window, so added cost (compared to previous
AND operation) is near zero.

dump operation gives current max_p value in a new TCA_RED_MAX_P
attribute.

Example on a 10Mbit link :

tc qdisc add dev $DEV parent 1:1 handle 10: est 1sec 8sec red \
   limit 400000 min 30000 max 90000 avpkt 1000 \
   burst 55 ecn adaptative bandwidth 10Mbit

# tc -s -d qdisc show dev eth3
...
qdisc red 10: parent 1:1 limit 400000b min 30000b max 90000b ecn
adaptative ewma 5 max_p=0.113335 Scell_log 15
 Sent 50414282 bytes 34504 pkt (dropped 35, overlimits 1392 requeues 0)
 rate 9749Kbit 831pps backlog 72056b 16p requeues 0
  marked 1357 early 35 pdrop 0 other 0

Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 57459185

include/linux/pkt_sched.h

+4 −2
Original line number Diff line number Diff line
@@ -181,6 +181,7 @@ enum { 
	TCA_RED_UNSPEC,

	TCA_RED_PARMS,

	TCA_RED_STAB,

	TCA_RED_MAX_P,

	__TCA_RED_MAX,

};
@@ -196,6 +197,7 @@ struct tc_red_qopt { 
	unsigned char	flags;

#define TC_RED_ECN		1

#define TC_RED_HARDDROP		2

#define TC_RED_ADAPTATIVE	4

};



struct tc_red_xstats {

include/net/red.h

+84 −17
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ 
#include <net/pkt_sched.h>

#include <net/inet_ecn.h>

#include <net/dsfield.h>

#include <linux/reciprocal_div.h>



/*	Random Early Detection (RED) algorithm.

	=======================================
@@ -87,6 +88,29 @@ 
	etc.

 */



/*

 * Adaptative RED : An Algorithm for Increasing the Robustness of RED's AQM

 * (Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker) August 2001

 *

 * Every 500 ms:

 *  if (avg > target and max_p <= 0.5)

 *   increase max_p : max_p += alpha;

 *  else if (avg < target and max_p >= 0.01)

 *   decrease max_p : max_p *= beta;

 *

 * target :[qth_min + 0.4*(qth_min - qth_max),

 *          qth_min + 0.6*(qth_min - qth_max)].

 * alpha : min(0.01, max_p / 4)

 * beta : 0.9

 * max_P is a Q0.32 fixed point number (with 32 bits mantissa)

 * max_P between 0.01 and 0.5 (1% - 50%) [ Its no longer a negative power of two ]

 */

#define RED_ONE_PERCENT ((u32)DIV_ROUND_CLOSEST(1ULL<<32, 100))



#define MAX_P_MIN (1 * RED_ONE_PERCENT)

#define MAX_P_MAX (50 * RED_ONE_PERCENT)

#define MAX_P_ALPHA(val) min(MAX_P_MIN, val / 4)



#define RED_STAB_SIZE	256

#define RED_STAB_MASK	(RED_STAB_SIZE - 1)
@@ -101,10 +125,14 @@ struct red_stats { 


struct red_parms {

	/* Parameters */

	u32		qth_min;	/* Min avg length threshold: A scaled */

	u32		qth_max;	/* Max avg length threshold: A scaled */

	u32		qth_min;	/* Min avg length threshold: Wlog scaled */

	u32		qth_max;	/* Max avg length threshold: Wlog scaled */

	u32		Scell_max;

	u32		Rmask;		/* Cached random mask, see red_rmask */

	u32		max_P;		/* probability, [0 .. 1.0] 32 scaled */

	u32		max_P_reciprocal; /* reciprocal_value(max_P / qth_delta) */

	u32		qth_delta;	/* max_th - min_th */

	u32		target_min;	/* min_th + 0.4*(max_th - min_th) */

	u32		target_max;	/* min_th + 0.6*(max_th - min_th) */

	u8		Scell_log;

	u8		Wlog;		/* log(W)		*/

	u8		Plog;		/* random number bits	*/
@@ -115,19 +143,22 @@ struct red_parms { 
					   number generation */

	u32		qR;		/* Cached random number */



	unsigned long	qavg;		/* Average queue length: A scaled */

	unsigned long	qavg;		/* Average queue length: Wlog scaled */

	ktime_t		qidlestart;	/* Start of current idle period */

};



static inline u32 red_rmask(u8 Plog)

static inline u32 red_maxp(u8 Plog)

{

	return Plog < 32 ? ((1 << Plog) - 1) : ~0UL;

	return Plog < 32 ? (~0U >> Plog) : ~0U;

}





static inline void red_set_parms(struct red_parms *p,

				 u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,

				 u8 Scell_log, u8 *stab)

{

	int delta = qth_max - qth_min;



	/* Reset average queue length, the value is strictly bound

	 * to the parameters below, reseting hurts a bit but leaving

	 * it might result in an unreasonable qavg for a while. --TGR
@@ -139,14 +170,29 @@ static inline void red_set_parms(struct red_parms *p, 
	p->qth_max	= qth_max << Wlog;

	p->Wlog		= Wlog;

	p->Plog		= Plog;

	p->Rmask	= red_rmask(Plog);

	if (delta < 0)

		delta = 1;

	p->qth_delta	= delta;

	p->max_P	= red_maxp(Plog);

	p->max_P	*= delta; /* max_P = (qth_max-qth_min)/2^Plog */



	p->max_P_reciprocal  = reciprocal_value(p->max_P / delta);



	/* RED Adaptative target :

	 * [min_th + 0.4*(min_th - max_th),

	 *  min_th + 0.6*(min_th - max_th)].

	 */

	delta /= 5;

	p->target_min = qth_min + 2*delta;

	p->target_max = qth_min + 3*delta;



	p->Scell_log	= Scell_log;

	p->Scell_max	= (255 << Scell_log);



	memcpy(p->Stab, stab, sizeof(p->Stab));

}



static inline int red_is_idling(struct red_parms *p)

static inline int red_is_idling(const struct red_parms *p)

{

	return p->qidlestart.tv64 != 0;

}
@@ -168,7 +214,7 @@ static inline void red_restart(struct red_parms *p) 
	p->qcount = -1;

}



static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p)

static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p)

{

	s64 delta = ktime_us_delta(ktime_get(), p->qidlestart);

	long us_idle = min_t(s64, delta, p->Scell_max);
@@ -215,7 +261,7 @@ static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p) 
	}

}



static inline unsigned long red_calc_qavg_no_idle_time(struct red_parms *p,

static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p,

						       unsigned int backlog)

{

	/*
@@ -230,7 +276,7 @@ static inline unsigned long red_calc_qavg_no_idle_time(struct red_parms *p, 
	return p->qavg + (backlog - (p->qavg >> p->Wlog));

}



static inline unsigned long red_calc_qavg(struct red_parms *p,

static inline unsigned long red_calc_qavg(const struct red_parms *p,

					  unsigned int backlog)

{

	if (!red_is_idling(p))
@@ -239,23 +285,24 @@ static inline unsigned long red_calc_qavg(struct red_parms *p, 
		return red_calc_qavg_from_idle_time(p);

}



static inline u32 red_random(struct red_parms *p)



static inline u32 red_random(const struct red_parms *p)

{

	return net_random() & p->Rmask;

	return reciprocal_divide(net_random(), p->max_P_reciprocal);

}



static inline int red_mark_probability(struct red_parms *p, unsigned long qavg)

static inline int red_mark_probability(const struct red_parms *p, unsigned long qavg)

{

	/* The formula used below causes questions.



	   OK. qR is random number in the interval 0..Rmask

	   OK. qR is random number in the interval

		(0..1/max_P)*(qth_max-qth_min)

	   i.e. 0..(2^Plog). If we used floating point

	   arithmetics, it would be: (2^Plog)*rnd_num,

	   where rnd_num is less 1.



	   Taking into account, that qavg have fixed

	   point at Wlog, and Plog is related to max_P by

	   max_P = (qth_max-qth_min)/2^Plog; two lines

	   point at Wlog, two lines

	   below have the following floating point equivalent:



	   max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
@@ -315,4 +362,24 @@ static inline int red_action(struct red_parms *p, unsigned long qavg) 
	return RED_DONT_MARK;

}



static inline void red_adaptative_algo(struct red_parms *p)

{

	unsigned long qavg;

	u32 max_p_delta;



	qavg = p->qavg;

	if (red_is_idling(p))

		qavg = red_calc_qavg_from_idle_time(p);



	/* p->qavg is fixed point number with point at Wlog */

	qavg >>= p->Wlog;



	if (qavg > p->target_max && p->max_P <= MAX_P_MAX)

		p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */

	else if (qavg < p->target_min && p->max_P >= MAX_P_MIN)

		p->max_P = (p->max_P/10)*9; /* maxp = maxp * Beta */



	max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta);

	p->max_P_reciprocal = reciprocal_value(max_p_delta);

}

#endif

lib/reciprocal_div.c

+2 −0
Original line number Diff line number Diff line 
#include <asm/div64.h>

#include <linux/reciprocal_div.h>

#include <linux/export.h>



u32 reciprocal_value(u32 k)

{
@@ -7,3 +8,4 @@ u32 reciprocal_value(u32 k) 
	do_div(val, k);

	return (u32)val;

}

EXPORT_SYMBOL(reciprocal_value);

net/sched/sch_red.c

+21 −0
Original line number Diff line number Diff line
@@ -39,6 +39,7 @@ 
struct red_sched_data {

	u32			limit;		/* HARD maximal queue length */

	unsigned char		flags;

	struct timer_list	adapt_timer;

	struct red_parms	parms;

	struct red_stats	stats;

	struct Qdisc		*qdisc;
@@ -161,6 +162,8 @@ static void red_reset(struct Qdisc *sch) 
static void red_destroy(struct Qdisc *sch)

{

	struct red_sched_data *q = qdisc_priv(sch);



	del_timer_sync(&q->adapt_timer);

	qdisc_destroy(q->qdisc);

}
@@ -209,6 +212,10 @@ static int red_change(struct Qdisc *sch, struct nlattr *opt) 
				 ctl->Plog, ctl->Scell_log,

				 nla_data(tb[TCA_RED_STAB]));



	del_timer(&q->adapt_timer);

	if (ctl->flags & TC_RED_ADAPTATIVE)

		mod_timer(&q->adapt_timer, jiffies + HZ/2);



	if (!q->qdisc->q.qlen)

		red_start_of_idle_period(&q->parms);
@@ -216,11 +223,24 @@ static int red_change(struct Qdisc *sch, struct nlattr *opt) 
	return 0;

}



static inline void red_adaptative_timer(unsigned long arg)

{

	struct Qdisc *sch = (struct Qdisc *)arg;

	struct red_sched_data *q = qdisc_priv(sch);

	spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));



	spin_lock(root_lock);

	red_adaptative_algo(&q->parms);

	mod_timer(&q->adapt_timer, jiffies + HZ/2);

	spin_unlock(root_lock);

}



static int red_init(struct Qdisc *sch, struct nlattr *opt)

{

	struct red_sched_data *q = qdisc_priv(sch);



	q->qdisc = &noop_qdisc;

	setup_timer(&q->adapt_timer, red_adaptative_timer, (unsigned long)sch);

	return red_change(sch, opt);

}
@@ -243,6 +263,7 @@ static int red_dump(struct Qdisc *sch, struct sk_buff *skb) 
	if (opts == NULL)

		goto nla_put_failure;

	NLA_PUT(skb, TCA_RED_PARMS, sizeof(opt), &opt);

	NLA_PUT_U32(skb, TCA_RED_MAX_P, q->parms.max_P);

	return nla_nest_end(skb, opts);



nla_put_failure: