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Diffstat (limited to 'include/net/red.h')
| -rw-r--r-- | include/net/red.h | 325 |
1 files changed, 325 insertions, 0 deletions
diff --git a/include/net/red.h b/include/net/red.h new file mode 100644 index 00000000000..2ed4358e329 --- /dev/null +++ b/include/net/red.h @@ -0,0 +1,325 @@ +#ifndef __NET_SCHED_RED_H +#define __NET_SCHED_RED_H + +#include <linux/config.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 !PSCHED_IS_PASTPERFECT(p->qidlestart); +} + +static inline void red_start_of_idle_period(struct red_parms *p) +{ + PSCHED_GET_TIME(p->qidlestart); +} + +static inline void red_end_of_idle_period(struct red_parms *p) +{ + PSCHED_SET_PASTPERFECT(p->qidlestart); +} + +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; + + PSCHED_GET_TIME(now); + us_idle = PSCHED_TDIFF_SAFE(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 * 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 |