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: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
index fb556dc594d3e799b12d956f86652a8077666d04..e41e0d4de24b12095acc6620eb765c5dfdd25dda 100644 (file)
--- a/include/linux/pkt_sched.h
+++ b/include/linux/pkt_sched.h
@@ -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 {

diff --git a/include/net/red.h b/include/net/red.h
index b72a3b83393604b29845514942a5cb8ad8729970..24606b22d01ef73292bf5e6e007635ec2e9ad019 100644 (file)
--- a/include/net/red.h
+++ b/include/net/red.h
@@ -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

diff --git a/lib/reciprocal_div.c b/lib/reciprocal_div.c
index 6a3bd48fa2a06e500d6695ac936a6ff4143775e4..75510e94f7d0b2fcd5736a4e0aeb9ff282da11d1 100644 (file)
--- a/lib/reciprocal_div.c
+++ b/lib/reciprocal_div.c
@@ -1,5 +1,6 @@
 #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);

diff --git a/net/sched/sch_red.c b/net/sched/sch_red.c
index d617161f8dd3904ddda7ac23da1178ccd03a79c4..8f5a85bf9d109b72dd3689a03080c25954a6dd5e 100644 (file)
--- a/net/sched/sch_red.c
+++ b/net/sched/sch_red.c
@@ -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: