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@xxxxxxxxx> --- include/linux/pkt_sched.h | 6 +- include/net/red.h | 101 +++++++++++++++++++++++++++++------- lib/reciprocal_div.c | 2 net/sched/sch_red.c | 21 +++++++ 4 files changed, 111 insertions(+), 19 deletions(-) diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h index fb556dc..e41e0d4 100644 --- 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 b72a3b8..f4e9533 100644 --- 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 6a3bd48..75510e9 100644 --- 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 d617161..8f5a85b 100644 --- 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: -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
