| #ifndef __NET_SCHED_RED_H |
| #define __NET_SCHED_RED_H |
| |
| #include <linux/types.h> |
| #include <net/pkt_sched.h> |
| #include <net/inet_ecn.h> |
| #include <net/dsfield.h> |
| |
| /* Random Early Detection (RED) algorithm. |
| ======================================= |
| |
| Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways |
| for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking. |
| |
| This file codes a "divisionless" version of RED algorithm |
| as written down in Fig.17 of the paper. |
| |
| Short description. |
| ------------------ |
| |
| When a new packet arrives we calculate the average queue length: |
| |
| avg = (1-W)*avg + W*current_queue_len, |
| |
| W is the filter time constant (chosen as 2^(-Wlog)), it controls |
| the inertia of the algorithm. To allow larger bursts, W should be |
| decreased. |
| |
| if (avg > th_max) -> packet marked (dropped). |
| if (avg < th_min) -> packet passes. |
| if (th_min < avg < th_max) we calculate probability: |
| |
| Pb = max_P * (avg - th_min)/(th_max-th_min) |
| |
| and mark (drop) packet with this probability. |
| Pb changes from 0 (at avg==th_min) to max_P (avg==th_max). |
| max_P should be small (not 1), usually 0.01..0.02 is good value. |
| |
| max_P is chosen as a number, so that max_P/(th_max-th_min) |
| is a negative power of two in order arithmetics to contain |
| only shifts. |
| |
| |
| Parameters, settable by user: |
| ----------------------------- |
| |
| qth_min - bytes (should be < qth_max/2) |
| qth_max - bytes (should be at least 2*qth_min and less limit) |
| Wlog - bits (<32) log(1/W). |
| Plog - bits (<32) |
| |
| Plog is related to max_P by formula: |
| |
| max_P = (qth_max-qth_min)/2^Plog; |
| |
| F.e. if qth_max=128K and qth_min=32K, then Plog=22 |
| corresponds to max_P=0.02 |
| |
| Scell_log |
| Stab |
| |
| Lookup table for log((1-W)^(t/t_ave). |
| |
| |
| NOTES: |
| |
| Upper bound on W. |
| ----------------- |
| |
| If you want to allow bursts of L packets of size S, |
| you should choose W: |
| |
| L + 1 - th_min/S < (1-(1-W)^L)/W |
| |
| th_min/S = 32 th_min/S = 4 |
| |
| log(W) L |
| -1 33 |
| -2 35 |
| -3 39 |
| -4 46 |
| -5 57 |
| -6 75 |
| -7 101 |
| -8 135 |
| -9 190 |
| etc. |
| */ |
| |
| #define RED_STAB_SIZE 256 |
| #define RED_STAB_MASK (RED_STAB_SIZE - 1) |
| |
| struct red_stats |
| { |
| u32 prob_drop; /* Early probability drops */ |
| u32 prob_mark; /* Early probability marks */ |
| u32 forced_drop; /* Forced drops, qavg > max_thresh */ |
| u32 forced_mark; /* Forced marks, qavg > max_thresh */ |
| u32 pdrop; /* Drops due to queue limits */ |
| u32 other; /* Drops due to drop() calls */ |
| u32 backlog; |
| }; |
| |
| struct red_parms |
| { |
| /* Parameters */ |
| u32 qth_min; /* Min avg length threshold: A scaled */ |
| u32 qth_max; /* Max avg length threshold: A scaled */ |
| u32 Scell_max; |
| u32 Rmask; /* Cached random mask, see red_rmask */ |
| u8 Scell_log; |
| u8 Wlog; /* log(W) */ |
| u8 Plog; /* random number bits */ |
| u8 Stab[RED_STAB_SIZE]; |
| |
| /* Variables */ |
| int qcount; /* Number of packets since last random |
| number generation */ |
| u32 qR; /* Cached random number */ |
| |
| unsigned long qavg; /* Average queue length: A scaled */ |
| psched_time_t qidlestart; /* Start of current idle period */ |
| }; |
| |
| static inline u32 red_rmask(u8 Plog) |
| { |
| return Plog < 32 ? ((1 << Plog) - 1) : ~0UL; |
| } |
| |
| 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) |
| { |
| /* 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 |
| */ |
| p->qavg = 0; |
| |
| p->qcount = -1; |
| p->qth_min = qth_min << Wlog; |
| p->qth_max = qth_max << Wlog; |
| p->Wlog = Wlog; |
| p->Plog = Plog; |
| p->Rmask = red_rmask(Plog); |
| 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) |
| { |
| return p->qidlestart != PSCHED_PASTPERFECT; |
| } |
| |
| static inline void red_start_of_idle_period(struct red_parms *p) |
| { |
| p->qidlestart = psched_get_time(); |
| } |
| |
| static inline void red_end_of_idle_period(struct red_parms *p) |
| { |
| p->qidlestart = PSCHED_PASTPERFECT; |
| } |
| |
| static inline void red_restart(struct red_parms *p) |
| { |
| red_end_of_idle_period(p); |
| p->qavg = 0; |
| p->qcount = -1; |
| } |
| |
| static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p) |
| { |
| psched_time_t now; |
| long us_idle; |
| int shift; |
| |
| now = psched_get_time(); |
| us_idle = psched_tdiff_bounded(now, p->qidlestart, p->Scell_max); |
| |
| /* |
| * The problem: ideally, average length queue recalcultion should |
| * be done over constant clock intervals. This is too expensive, so |
| * that the calculation is driven by outgoing packets. |
| * When the queue is idle we have to model this clock by hand. |
| * |
| * SF+VJ proposed to "generate": |
| * |
| * m = idletime / (average_pkt_size / bandwidth) |
| * |
| * dummy packets as a burst after idle time, i.e. |
| * |
| * p->qavg *= (1-W)^m |
| * |
| * This is an apparently overcomplicated solution (f.e. we have to |
| * precompute a table to make this calculation in reasonable time) |
| * I believe that a simpler model may be used here, |
| * but it is field for experiments. |
| */ |
| |
| shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK]; |
| |
| if (shift) |
| return p->qavg >> shift; |
| else { |
| /* Approximate initial part of exponent with linear function: |
| * |
| * (1-W)^m ~= 1-mW + ... |
| * |
| * Seems, it is the best solution to |
| * problem of too coarse exponent tabulation. |
| */ |
| us_idle = (p->qavg * (u64)us_idle) >> p->Scell_log; |
| |
| if (us_idle < (p->qavg >> 1)) |
| return p->qavg - us_idle; |
| else |
| return p->qavg >> 1; |
| } |
| } |
| |
| static inline unsigned long red_calc_qavg_no_idle_time(struct red_parms *p, |
| unsigned int backlog) |
| { |
| /* |
| * NOTE: p->qavg is fixed point number with point at Wlog. |
| * The formula below is equvalent to floating point |
| * version: |
| * |
| * qavg = qavg*(1-W) + backlog*W; |
| * |
| * --ANK (980924) |
| */ |
| return p->qavg + (backlog - (p->qavg >> p->Wlog)); |
| } |
| |
| static inline unsigned long red_calc_qavg(struct red_parms *p, |
| unsigned int backlog) |
| { |
| if (!red_is_idling(p)) |
| return red_calc_qavg_no_idle_time(p, backlog); |
| else |
| return red_calc_qavg_from_idle_time(p); |
| } |
| |
| static inline u32 red_random(struct red_parms *p) |
| { |
| return net_random() & p->Rmask; |
| } |
| |
| static inline int red_mark_probability(struct red_parms *p, unsigned long qavg) |
| { |
| /* The formula used below causes questions. |
| |
| OK. qR is random number in the interval 0..Rmask |
| 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 |
| below have the following floating point equivalent: |
| |
| max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount |
| |
| Any questions? --ANK (980924) |
| */ |
| return !(((qavg - p->qth_min) >> p->Wlog) * p->qcount < p->qR); |
| } |
| |
| enum { |
| RED_BELOW_MIN_THRESH, |
| RED_BETWEEN_TRESH, |
| RED_ABOVE_MAX_TRESH, |
| }; |
| |
| static inline int red_cmp_thresh(struct red_parms *p, unsigned long qavg) |
| { |
| if (qavg < p->qth_min) |
| return RED_BELOW_MIN_THRESH; |
| else if (qavg >= p->qth_max) |
| return RED_ABOVE_MAX_TRESH; |
| else |
| return RED_BETWEEN_TRESH; |
| } |
| |
| enum { |
| RED_DONT_MARK, |
| RED_PROB_MARK, |
| RED_HARD_MARK, |
| }; |
| |
| static inline int red_action(struct red_parms *p, unsigned long qavg) |
| { |
| switch (red_cmp_thresh(p, qavg)) { |
| case RED_BELOW_MIN_THRESH: |
| p->qcount = -1; |
| return RED_DONT_MARK; |
| |
| case RED_BETWEEN_TRESH: |
| if (++p->qcount) { |
| if (red_mark_probability(p, qavg)) { |
| p->qcount = 0; |
| p->qR = red_random(p); |
| return RED_PROB_MARK; |
| } |
| } else |
| p->qR = red_random(p); |
| |
| return RED_DONT_MARK; |
| |
| case RED_ABOVE_MAX_TRESH: |
| p->qcount = -1; |
| return RED_HARD_MARK; |
| } |
| |
| BUG(); |
| return RED_DONT_MARK; |
| } |
| |
| #endif |