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1 | #ifndef __NET_SCHED_RED_H |
2 | #define __NET_SCHED_RED_H | |
3 | ||
a7834745 TG |
4 | #include <linux/types.h> |
5 | #include <net/pkt_sched.h> | |
6 | #include <net/inet_ecn.h> | |
7 | #include <net/dsfield.h> | |
8 | ||
9 | /* Random Early Detection (RED) algorithm. | |
10 | ======================================= | |
11 | ||
12 | Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways | |
13 | for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking. | |
14 | ||
15 | This file codes a "divisionless" version of RED algorithm | |
16 | as written down in Fig.17 of the paper. | |
17 | ||
18 | Short description. | |
19 | ------------------ | |
20 | ||
21 | When a new packet arrives we calculate the average queue length: | |
22 | ||
23 | avg = (1-W)*avg + W*current_queue_len, | |
24 | ||
25 | W is the filter time constant (chosen as 2^(-Wlog)), it controls | |
26 | the inertia of the algorithm. To allow larger bursts, W should be | |
27 | decreased. | |
28 | ||
29 | if (avg > th_max) -> packet marked (dropped). | |
30 | if (avg < th_min) -> packet passes. | |
31 | if (th_min < avg < th_max) we calculate probability: | |
32 | ||
33 | Pb = max_P * (avg - th_min)/(th_max-th_min) | |
34 | ||
35 | and mark (drop) packet with this probability. | |
36 | Pb changes from 0 (at avg==th_min) to max_P (avg==th_max). | |
37 | max_P should be small (not 1), usually 0.01..0.02 is good value. | |
38 | ||
39 | max_P is chosen as a number, so that max_P/(th_max-th_min) | |
40 | is a negative power of two in order arithmetics to contain | |
41 | only shifts. | |
42 | ||
43 | ||
44 | Parameters, settable by user: | |
45 | ----------------------------- | |
46 | ||
47 | qth_min - bytes (should be < qth_max/2) | |
48 | qth_max - bytes (should be at least 2*qth_min and less limit) | |
49 | Wlog - bits (<32) log(1/W). | |
50 | Plog - bits (<32) | |
51 | ||
52 | Plog is related to max_P by formula: | |
53 | ||
54 | max_P = (qth_max-qth_min)/2^Plog; | |
55 | ||
56 | F.e. if qth_max=128K and qth_min=32K, then Plog=22 | |
57 | corresponds to max_P=0.02 | |
58 | ||
59 | Scell_log | |
60 | Stab | |
61 | ||
62 | Lookup table for log((1-W)^(t/t_ave). | |
63 | ||
64 | ||
65 | NOTES: | |
66 | ||
67 | Upper bound on W. | |
68 | ----------------- | |
69 | ||
70 | If you want to allow bursts of L packets of size S, | |
71 | you should choose W: | |
72 | ||
73 | L + 1 - th_min/S < (1-(1-W)^L)/W | |
74 | ||
75 | th_min/S = 32 th_min/S = 4 | |
76 | ||
77 | log(W) L | |
78 | -1 33 | |
79 | -2 35 | |
80 | -3 39 | |
81 | -4 46 | |
82 | -5 57 | |
83 | -6 75 | |
84 | -7 101 | |
85 | -8 135 | |
86 | -9 190 | |
87 | etc. | |
88 | */ | |
89 | ||
90 | #define RED_STAB_SIZE 256 | |
91 | #define RED_STAB_MASK (RED_STAB_SIZE - 1) | |
92 | ||
93 | struct red_stats | |
94 | { | |
95 | u32 prob_drop; /* Early probability drops */ | |
96 | u32 prob_mark; /* Early probability marks */ | |
97 | u32 forced_drop; /* Forced drops, qavg > max_thresh */ | |
98 | u32 forced_mark; /* Forced marks, qavg > max_thresh */ | |
99 | u32 pdrop; /* Drops due to queue limits */ | |
100 | u32 other; /* Drops due to drop() calls */ | |
101 | u32 backlog; | |
102 | }; | |
103 | ||
104 | struct red_parms | |
105 | { | |
106 | /* Parameters */ | |
107 | u32 qth_min; /* Min avg length threshold: A scaled */ | |
108 | u32 qth_max; /* Max avg length threshold: A scaled */ | |
109 | u32 Scell_max; | |
110 | u32 Rmask; /* Cached random mask, see red_rmask */ | |
111 | u8 Scell_log; | |
112 | u8 Wlog; /* log(W) */ | |
113 | u8 Plog; /* random number bits */ | |
114 | u8 Stab[RED_STAB_SIZE]; | |
115 | ||
116 | /* Variables */ | |
117 | int qcount; /* Number of packets since last random | |
118 | number generation */ | |
119 | u32 qR; /* Cached random number */ | |
120 | ||
121 | unsigned long qavg; /* Average queue length: A scaled */ | |
122 | psched_time_t qidlestart; /* Start of current idle period */ | |
123 | }; | |
124 | ||
125 | static inline u32 red_rmask(u8 Plog) | |
126 | { | |
127 | return Plog < 32 ? ((1 << Plog) - 1) : ~0UL; | |
128 | } | |
129 | ||
130 | static inline void red_set_parms(struct red_parms *p, | |
131 | u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog, | |
132 | u8 Scell_log, u8 *stab) | |
133 | { | |
134 | /* Reset average queue length, the value is strictly bound | |
135 | * to the parameters below, reseting hurts a bit but leaving | |
136 | * it might result in an unreasonable qavg for a while. --TGR | |
137 | */ | |
138 | p->qavg = 0; | |
139 | ||
140 | p->qcount = -1; | |
141 | p->qth_min = qth_min << Wlog; | |
142 | p->qth_max = qth_max << Wlog; | |
143 | p->Wlog = Wlog; | |
144 | p->Plog = Plog; | |
145 | p->Rmask = red_rmask(Plog); | |
146 | p->Scell_log = Scell_log; | |
147 | p->Scell_max = (255 << Scell_log); | |
148 | ||
149 | memcpy(p->Stab, stab, sizeof(p->Stab)); | |
150 | } | |
151 | ||
152 | static inline int red_is_idling(struct red_parms *p) | |
153 | { | |
a084980d | 154 | return p->qidlestart != PSCHED_PASTPERFECT; |
a7834745 TG |
155 | } |
156 | ||
157 | static inline void red_start_of_idle_period(struct red_parms *p) | |
158 | { | |
3bebcda2 | 159 | p->qidlestart = psched_get_time(); |
a7834745 TG |
160 | } |
161 | ||
162 | static inline void red_end_of_idle_period(struct red_parms *p) | |
163 | { | |
a084980d | 164 | p->qidlestart = PSCHED_PASTPERFECT; |
a7834745 TG |
165 | } |
166 | ||
167 | static inline void red_restart(struct red_parms *p) | |
168 | { | |
169 | red_end_of_idle_period(p); | |
170 | p->qavg = 0; | |
171 | p->qcount = -1; | |
172 | } | |
173 | ||
174 | static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p) | |
175 | { | |
176 | psched_time_t now; | |
177 | long us_idle; | |
178 | int shift; | |
179 | ||
3bebcda2 | 180 | now = psched_get_time(); |
03cc45c0 | 181 | us_idle = psched_tdiff_bounded(now, p->qidlestart, p->Scell_max); |
a7834745 TG |
182 | |
183 | /* | |
184 | * The problem: ideally, average length queue recalcultion should | |
185 | * be done over constant clock intervals. This is too expensive, so | |
186 | * that the calculation is driven by outgoing packets. | |
187 | * When the queue is idle we have to model this clock by hand. | |
188 | * | |
189 | * SF+VJ proposed to "generate": | |
190 | * | |
191 | * m = idletime / (average_pkt_size / bandwidth) | |
192 | * | |
193 | * dummy packets as a burst after idle time, i.e. | |
194 | * | |
195 | * p->qavg *= (1-W)^m | |
196 | * | |
197 | * This is an apparently overcomplicated solution (f.e. we have to | |
198 | * precompute a table to make this calculation in reasonable time) | |
199 | * I believe that a simpler model may be used here, | |
200 | * but it is field for experiments. | |
201 | */ | |
202 | ||
203 | shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK]; | |
204 | ||
205 | if (shift) | |
206 | return p->qavg >> shift; | |
207 | else { | |
208 | /* Approximate initial part of exponent with linear function: | |
209 | * | |
210 | * (1-W)^m ~= 1-mW + ... | |
211 | * | |
212 | * Seems, it is the best solution to | |
213 | * problem of too coarse exponent tabulation. | |
214 | */ | |
c4c0ce5c | 215 | us_idle = (p->qavg * (u64)us_idle) >> p->Scell_log; |
a7834745 TG |
216 | |
217 | if (us_idle < (p->qavg >> 1)) | |
218 | return p->qavg - us_idle; | |
219 | else | |
220 | return p->qavg >> 1; | |
221 | } | |
222 | } | |
223 | ||
224 | static inline unsigned long red_calc_qavg_no_idle_time(struct red_parms *p, | |
225 | unsigned int backlog) | |
226 | { | |
227 | /* | |
228 | * NOTE: p->qavg is fixed point number with point at Wlog. | |
229 | * The formula below is equvalent to floating point | |
230 | * version: | |
231 | * | |
232 | * qavg = qavg*(1-W) + backlog*W; | |
233 | * | |
234 | * --ANK (980924) | |
235 | */ | |
236 | return p->qavg + (backlog - (p->qavg >> p->Wlog)); | |
237 | } | |
238 | ||
239 | static inline unsigned long red_calc_qavg(struct red_parms *p, | |
240 | unsigned int backlog) | |
241 | { | |
242 | if (!red_is_idling(p)) | |
243 | return red_calc_qavg_no_idle_time(p, backlog); | |
244 | else | |
245 | return red_calc_qavg_from_idle_time(p); | |
246 | } | |
247 | ||
248 | static inline u32 red_random(struct red_parms *p) | |
249 | { | |
250 | return net_random() & p->Rmask; | |
251 | } | |
252 | ||
253 | static inline int red_mark_probability(struct red_parms *p, unsigned long qavg) | |
254 | { | |
255 | /* The formula used below causes questions. | |
256 | ||
257 | OK. qR is random number in the interval 0..Rmask | |
258 | i.e. 0..(2^Plog). If we used floating point | |
259 | arithmetics, it would be: (2^Plog)*rnd_num, | |
260 | where rnd_num is less 1. | |
261 | ||
262 | Taking into account, that qavg have fixed | |
263 | point at Wlog, and Plog is related to max_P by | |
264 | max_P = (qth_max-qth_min)/2^Plog; two lines | |
265 | below have the following floating point equivalent: | |
266 | ||
267 | max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount | |
268 | ||
269 | Any questions? --ANK (980924) | |
270 | */ | |
271 | return !(((qavg - p->qth_min) >> p->Wlog) * p->qcount < p->qR); | |
272 | } | |
273 | ||
274 | enum { | |
275 | RED_BELOW_MIN_THRESH, | |
276 | RED_BETWEEN_TRESH, | |
277 | RED_ABOVE_MAX_TRESH, | |
278 | }; | |
279 | ||
280 | static inline int red_cmp_thresh(struct red_parms *p, unsigned long qavg) | |
281 | { | |
282 | if (qavg < p->qth_min) | |
283 | return RED_BELOW_MIN_THRESH; | |
284 | else if (qavg >= p->qth_max) | |
285 | return RED_ABOVE_MAX_TRESH; | |
286 | else | |
287 | return RED_BETWEEN_TRESH; | |
288 | } | |
289 | ||
290 | enum { | |
291 | RED_DONT_MARK, | |
292 | RED_PROB_MARK, | |
293 | RED_HARD_MARK, | |
294 | }; | |
295 | ||
296 | static inline int red_action(struct red_parms *p, unsigned long qavg) | |
297 | { | |
298 | switch (red_cmp_thresh(p, qavg)) { | |
299 | case RED_BELOW_MIN_THRESH: | |
300 | p->qcount = -1; | |
301 | return RED_DONT_MARK; | |
302 | ||
303 | case RED_BETWEEN_TRESH: | |
304 | if (++p->qcount) { | |
305 | if (red_mark_probability(p, qavg)) { | |
306 | p->qcount = 0; | |
307 | p->qR = red_random(p); | |
308 | return RED_PROB_MARK; | |
309 | } | |
310 | } else | |
311 | p->qR = red_random(p); | |
312 | ||
313 | return RED_DONT_MARK; | |
314 | ||
315 | case RED_ABOVE_MAX_TRESH: | |
316 | p->qcount = -1; | |
317 | return RED_HARD_MARK; | |
318 | } | |
319 | ||
320 | BUG(); | |
321 | return RED_DONT_MARK; | |
322 | } | |
323 | ||
324 | #endif |