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>
This commit is contained in:
Eric Dumazet
David S. Miller
parent
57459185a1
commit
8af2a218de
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@ -181,6 +181,7 @@ enum {
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TCA_RED_UNSPEC,
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TCA_RED_PARMS,
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TCA_RED_STAB,
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TCA_RED_MAX_P,
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__TCA_RED_MAX,
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};
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@ -194,8 +195,9 @@ struct tc_red_qopt {
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unsigned char Plog; /* log(P_max/(qth_max-qth_min)) */
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unsigned char Scell_log; /* cell size for idle damping */
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unsigned char flags;
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#define TC_RED_ECN 1
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#define TC_RED_HARDDROP 2
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#define TC_RED_ECN 1
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#define TC_RED_HARDDROP 2
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#define TC_RED_ADAPTATIVE 4
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};
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struct tc_red_xstats {
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@ -5,6 +5,7 @@
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#include <net/pkt_sched.h>
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#include <net/inet_ecn.h>
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#include <net/dsfield.h>
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#include <linux/reciprocal_div.h>
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/* Random Early Detection (RED) algorithm.
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=======================================
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@ -87,6 +88,29 @@
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etc.
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*/
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/*
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* Adaptative RED : An Algorithm for Increasing the Robustness of RED's AQM
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* (Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker) August 2001
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*
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* Every 500 ms:
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* if (avg > target and max_p <= 0.5)
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* increase max_p : max_p += alpha;
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* else if (avg < target and max_p >= 0.01)
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* decrease max_p : max_p *= beta;
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*
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* target :[qth_min + 0.4*(qth_min - qth_max),
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* qth_min + 0.6*(qth_min - qth_max)].
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* alpha : min(0.01, max_p / 4)
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* beta : 0.9
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* max_P is a Q0.32 fixed point number (with 32 bits mantissa)
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* max_P between 0.01 and 0.5 (1% - 50%) [ Its no longer a negative power of two ]
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*/
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#define RED_ONE_PERCENT ((u32)DIV_ROUND_CLOSEST(1ULL<<32, 100))
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#define MAX_P_MIN (1 * RED_ONE_PERCENT)
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#define MAX_P_MAX (50 * RED_ONE_PERCENT)
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#define MAX_P_ALPHA(val) min(MAX_P_MIN, val / 4)
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#define RED_STAB_SIZE 256
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#define RED_STAB_MASK (RED_STAB_SIZE - 1)
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@ -101,10 +125,14 @@ struct red_stats {
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struct red_parms {
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/* Parameters */
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u32 qth_min; /* Min avg length threshold: A scaled */
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u32 qth_max; /* Max avg length threshold: A scaled */
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u32 qth_min; /* Min avg length threshold: Wlog scaled */
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u32 qth_max; /* Max avg length threshold: Wlog scaled */
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u32 Scell_max;
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u32 Rmask; /* Cached random mask, see red_rmask */
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u32 max_P; /* probability, [0 .. 1.0] 32 scaled */
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u32 max_P_reciprocal; /* reciprocal_value(max_P / qth_delta) */
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u32 qth_delta; /* max_th - min_th */
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u32 target_min; /* min_th + 0.4*(max_th - min_th) */
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u32 target_max; /* min_th + 0.6*(max_th - min_th) */
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u8 Scell_log;
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u8 Wlog; /* log(W) */
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u8 Plog; /* random number bits */
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@ -115,19 +143,22 @@ struct red_parms {
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number generation */
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u32 qR; /* Cached random number */
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unsigned long qavg; /* Average queue length: A scaled */
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unsigned long qavg; /* Average queue length: Wlog scaled */
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ktime_t qidlestart; /* Start of current idle period */
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};
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static inline u32 red_rmask(u8 Plog)
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static inline u32 red_maxp(u8 Plog)
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{
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return Plog < 32 ? ((1 << Plog) - 1) : ~0UL;
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return Plog < 32 ? (~0U >> Plog) : ~0U;
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}
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static inline void red_set_parms(struct red_parms *p,
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u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
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u8 Scell_log, u8 *stab)
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{
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int delta = qth_max - qth_min;
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/* Reset average queue length, the value is strictly bound
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* to the parameters below, reseting hurts a bit but leaving
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* it might result in an unreasonable qavg for a while. --TGR
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@ -139,14 +170,29 @@ static inline void red_set_parms(struct red_parms *p,
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p->qth_max = qth_max << Wlog;
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p->Wlog = Wlog;
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p->Plog = Plog;
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p->Rmask = red_rmask(Plog);
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if (delta < 0)
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delta = 1;
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p->qth_delta = delta;
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p->max_P = red_maxp(Plog);
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p->max_P *= delta; /* max_P = (qth_max-qth_min)/2^Plog */
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p->max_P_reciprocal = reciprocal_value(p->max_P / delta);
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/* RED Adaptative target :
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* [min_th + 0.4*(min_th - max_th),
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* min_th + 0.6*(min_th - max_th)].
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*/
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delta /= 5;
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p->target_min = qth_min + 2*delta;
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p->target_max = qth_min + 3*delta;
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p->Scell_log = Scell_log;
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p->Scell_max = (255 << Scell_log);
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memcpy(p->Stab, stab, sizeof(p->Stab));
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}
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static inline int red_is_idling(struct red_parms *p)
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static inline int red_is_idling(const struct red_parms *p)
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{
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return p->qidlestart.tv64 != 0;
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}
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@ -168,7 +214,7 @@ static inline void red_restart(struct red_parms *p)
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p->qcount = -1;
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}
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static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p)
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static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p)
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{
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s64 delta = ktime_us_delta(ktime_get(), p->qidlestart);
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long us_idle = min_t(s64, delta, p->Scell_max);
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@ -215,7 +261,7 @@ static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p)
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}
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}
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static inline unsigned long red_calc_qavg_no_idle_time(struct red_parms *p,
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static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p,
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unsigned int backlog)
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{
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/*
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@ -230,7 +276,7 @@ static inline unsigned long red_calc_qavg_no_idle_time(struct red_parms *p,
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return p->qavg + (backlog - (p->qavg >> p->Wlog));
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}
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static inline unsigned long red_calc_qavg(struct red_parms *p,
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static inline unsigned long red_calc_qavg(const struct red_parms *p,
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unsigned int backlog)
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{
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if (!red_is_idling(p))
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@ -239,23 +285,24 @@ static inline unsigned long red_calc_qavg(struct red_parms *p,
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return red_calc_qavg_from_idle_time(p);
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}
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static inline u32 red_random(struct red_parms *p)
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static inline u32 red_random(const struct red_parms *p)
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{
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return net_random() & p->Rmask;
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return reciprocal_divide(net_random(), p->max_P_reciprocal);
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}
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static inline int red_mark_probability(struct red_parms *p, unsigned long qavg)
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static inline int red_mark_probability(const struct red_parms *p, unsigned long qavg)
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{
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/* The formula used below causes questions.
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OK. qR is random number in the interval 0..Rmask
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OK. qR is random number in the interval
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(0..1/max_P)*(qth_max-qth_min)
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i.e. 0..(2^Plog). If we used floating point
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arithmetics, it would be: (2^Plog)*rnd_num,
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where rnd_num is less 1.
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Taking into account, that qavg have fixed
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point at Wlog, and Plog is related to max_P by
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max_P = (qth_max-qth_min)/2^Plog; two lines
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point at Wlog, two lines
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below have the following floating point equivalent:
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max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
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@ -315,4 +362,24 @@ static inline int red_action(struct red_parms *p, unsigned long qavg)
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return RED_DONT_MARK;
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}
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static inline void red_adaptative_algo(struct red_parms *p)
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{
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unsigned long qavg;
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u32 max_p_delta;
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qavg = p->qavg;
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if (red_is_idling(p))
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qavg = red_calc_qavg_from_idle_time(p);
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/* p->qavg is fixed point number with point at Wlog */
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qavg >>= p->Wlog;
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if (qavg > p->target_max && p->max_P <= MAX_P_MAX)
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p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */
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else if (qavg < p->target_min && p->max_P >= MAX_P_MIN)
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p->max_P = (p->max_P/10)*9; /* maxp = maxp * Beta */
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max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta);
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p->max_P_reciprocal = reciprocal_value(max_p_delta);
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}
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#endif
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@ -1,5 +1,6 @@
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#include <asm/div64.h>
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#include <linux/reciprocal_div.h>
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#include <linux/export.h>
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u32 reciprocal_value(u32 k)
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{
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@ -7,3 +8,4 @@ u32 reciprocal_value(u32 k)
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do_div(val, k);
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return (u32)val;
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}
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EXPORT_SYMBOL(reciprocal_value);
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@ -39,6 +39,7 @@
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struct red_sched_data {
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u32 limit; /* HARD maximal queue length */
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unsigned char flags;
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struct timer_list adapt_timer;
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struct red_parms parms;
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struct red_stats stats;
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struct Qdisc *qdisc;
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@ -161,6 +162,8 @@ static void red_reset(struct Qdisc *sch)
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static void red_destroy(struct Qdisc *sch)
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{
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struct red_sched_data *q = qdisc_priv(sch);
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del_timer_sync(&q->adapt_timer);
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qdisc_destroy(q->qdisc);
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}
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@ -209,6 +212,10 @@ static int red_change(struct Qdisc *sch, struct nlattr *opt)
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ctl->Plog, ctl->Scell_log,
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nla_data(tb[TCA_RED_STAB]));
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del_timer(&q->adapt_timer);
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if (ctl->flags & TC_RED_ADAPTATIVE)
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mod_timer(&q->adapt_timer, jiffies + HZ/2);
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if (!q->qdisc->q.qlen)
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red_start_of_idle_period(&q->parms);
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@ -216,11 +223,24 @@ static int red_change(struct Qdisc *sch, struct nlattr *opt)
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return 0;
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}
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static inline void red_adaptative_timer(unsigned long arg)
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{
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struct Qdisc *sch = (struct Qdisc *)arg;
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struct red_sched_data *q = qdisc_priv(sch);
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spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));
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spin_lock(root_lock);
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red_adaptative_algo(&q->parms);
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mod_timer(&q->adapt_timer, jiffies + HZ/2);
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spin_unlock(root_lock);
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}
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static int red_init(struct Qdisc *sch, struct nlattr *opt)
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{
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struct red_sched_data *q = qdisc_priv(sch);
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q->qdisc = &noop_qdisc;
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setup_timer(&q->adapt_timer, red_adaptative_timer, (unsigned long)sch);
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return red_change(sch, opt);
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}
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@ -243,6 +263,7 @@ static int red_dump(struct Qdisc *sch, struct sk_buff *skb)
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if (opts == NULL)
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goto nla_put_failure;
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NLA_PUT(skb, TCA_RED_PARMS, sizeof(opt), &opt);
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NLA_PUT_U32(skb, TCA_RED_MAX_P, q->parms.max_P);
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return nla_nest_end(skb, opts);
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nla_put_failure:
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