Commit 8af2a218 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller

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
......@@ -181,6 +181,7 @@ enum {
TCA_RED_UNSPEC,
TCA_RED_PARMS,
TCA_RED_STAB,
TCA_RED_MAX_P,
__TCA_RED_MAX,
};
......@@ -194,8 +195,9 @@ struct tc_red_qopt {
unsigned char Plog; /* log(P_max/(qth_max-qth_min)) */
unsigned char Scell_log; /* cell size for idle damping */
unsigned char flags;
#define TC_RED_ECN 1
#define TC_RED_HARDDROP 2
#define TC_RED_ECN 1
#define TC_RED_HARDDROP 2
#define TC_RED_ADAPTATIVE 4
};
struct tc_red_xstats {
......
......@@ -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
#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);
......@@ -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:
......
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