Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6
[linux-2.6.git] / include / net / red.h
1 #ifndef __NET_SCHED_RED_H
2 #define __NET_SCHED_RED_H
3
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         u32             prob_drop;      /* Early probability drops */
95         u32             prob_mark;      /* Early probability marks */
96         u32             forced_drop;    /* Forced drops, qavg > max_thresh */
97         u32             forced_mark;    /* Forced marks, qavg > max_thresh */
98         u32             pdrop;          /* Drops due to queue limits */
99         u32             other;          /* Drops due to drop() calls */
100         u32             backlog;
101 };
102
103 struct red_parms {
104         /* Parameters */
105         u32             qth_min;        /* Min avg length threshold: A scaled */
106         u32             qth_max;        /* Max avg length threshold: A scaled */
107         u32             Scell_max;
108         u32             Rmask;          /* Cached random mask, see red_rmask */
109         u8              Scell_log;
110         u8              Wlog;           /* log(W)               */
111         u8              Plog;           /* random number bits   */
112         u8              Stab[RED_STAB_SIZE];
113
114         /* Variables */
115         int             qcount;         /* Number of packets since last random
116                                            number generation */
117         u32             qR;             /* Cached random number */
118
119         unsigned long   qavg;           /* Average queue length: A scaled */
120         psched_time_t   qidlestart;     /* Start of current idle period */
121 };
122
123 static inline u32 red_rmask(u8 Plog)
124 {
125         return Plog < 32 ? ((1 << Plog) - 1) : ~0UL;
126 }
127
128 static inline void red_set_parms(struct red_parms *p,
129                                  u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
130                                  u8 Scell_log, u8 *stab)
131 {
132         /* Reset average queue length, the value is strictly bound
133          * to the parameters below, reseting hurts a bit but leaving
134          * it might result in an unreasonable qavg for a while. --TGR
135          */
136         p->qavg         = 0;
137
138         p->qcount       = -1;
139         p->qth_min      = qth_min << Wlog;
140         p->qth_max      = qth_max << Wlog;
141         p->Wlog         = Wlog;
142         p->Plog         = Plog;
143         p->Rmask        = red_rmask(Plog);
144         p->Scell_log    = Scell_log;
145         p->Scell_max    = (255 << Scell_log);
146
147         memcpy(p->Stab, stab, sizeof(p->Stab));
148 }
149
150 static inline int red_is_idling(struct red_parms *p)
151 {
152         return p->qidlestart != PSCHED_PASTPERFECT;
153 }
154
155 static inline void red_start_of_idle_period(struct red_parms *p)
156 {
157         p->qidlestart = psched_get_time();
158 }
159
160 static inline void red_end_of_idle_period(struct red_parms *p)
161 {
162         p->qidlestart = PSCHED_PASTPERFECT;
163 }
164
165 static inline void red_restart(struct red_parms *p)
166 {
167         red_end_of_idle_period(p);
168         p->qavg = 0;
169         p->qcount = -1;
170 }
171
172 static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p)
173 {
174         psched_time_t now;
175         long us_idle;
176         int  shift;
177
178         now = psched_get_time();
179         us_idle = psched_tdiff_bounded(now, p->qidlestart, p->Scell_max);
180
181         /*
182          * The problem: ideally, average length queue recalcultion should
183          * be done over constant clock intervals. This is too expensive, so
184          * that the calculation is driven by outgoing packets.
185          * When the queue is idle we have to model this clock by hand.
186          *
187          * SF+VJ proposed to "generate":
188          *
189          *      m = idletime / (average_pkt_size / bandwidth)
190          *
191          * dummy packets as a burst after idle time, i.e.
192          *
193          *      p->qavg *= (1-W)^m
194          *
195          * This is an apparently overcomplicated solution (f.e. we have to
196          * precompute a table to make this calculation in reasonable time)
197          * I believe that a simpler model may be used here,
198          * but it is field for experiments.
199          */
200
201         shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK];
202
203         if (shift)
204                 return p->qavg >> shift;
205         else {
206                 /* Approximate initial part of exponent with linear function:
207                  *
208                  *      (1-W)^m ~= 1-mW + ...
209                  *
210                  * Seems, it is the best solution to
211                  * problem of too coarse exponent tabulation.
212                  */
213                 us_idle = (p->qavg * (u64)us_idle) >> p->Scell_log;
214
215                 if (us_idle < (p->qavg >> 1))
216                         return p->qavg - us_idle;
217                 else
218                         return p->qavg >> 1;
219         }
220 }
221
222 static inline unsigned long red_calc_qavg_no_idle_time(struct red_parms *p,
223                                                        unsigned int backlog)
224 {
225         /*
226          * NOTE: p->qavg is fixed point number with point at Wlog.
227          * The formula below is equvalent to floating point
228          * version:
229          *
230          *      qavg = qavg*(1-W) + backlog*W;
231          *
232          * --ANK (980924)
233          */
234         return p->qavg + (backlog - (p->qavg >> p->Wlog));
235 }
236
237 static inline unsigned long red_calc_qavg(struct red_parms *p,
238                                           unsigned int backlog)
239 {
240         if (!red_is_idling(p))
241                 return red_calc_qavg_no_idle_time(p, backlog);
242         else
243                 return red_calc_qavg_from_idle_time(p);
244 }
245
246 static inline u32 red_random(struct red_parms *p)
247 {
248         return net_random() & p->Rmask;
249 }
250
251 static inline int red_mark_probability(struct red_parms *p, unsigned long qavg)
252 {
253         /* The formula used below causes questions.
254
255            OK. qR is random number in the interval 0..Rmask
256            i.e. 0..(2^Plog). If we used floating point
257            arithmetics, it would be: (2^Plog)*rnd_num,
258            where rnd_num is less 1.
259
260            Taking into account, that qavg have fixed
261            point at Wlog, and Plog is related to max_P by
262            max_P = (qth_max-qth_min)/2^Plog; two lines
263            below have the following floating point equivalent:
264
265            max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
266
267            Any questions? --ANK (980924)
268          */
269         return !(((qavg - p->qth_min) >> p->Wlog) * p->qcount < p->qR);
270 }
271
272 enum {
273         RED_BELOW_MIN_THRESH,
274         RED_BETWEEN_TRESH,
275         RED_ABOVE_MAX_TRESH,
276 };
277
278 static inline int red_cmp_thresh(struct red_parms *p, unsigned long qavg)
279 {
280         if (qavg < p->qth_min)
281                 return RED_BELOW_MIN_THRESH;
282         else if (qavg >= p->qth_max)
283                 return RED_ABOVE_MAX_TRESH;
284         else
285                 return RED_BETWEEN_TRESH;
286 }
287
288 enum {
289         RED_DONT_MARK,
290         RED_PROB_MARK,
291         RED_HARD_MARK,
292 };
293
294 static inline int red_action(struct red_parms *p, unsigned long qavg)
295 {
296         switch (red_cmp_thresh(p, qavg)) {
297                 case RED_BELOW_MIN_THRESH:
298                         p->qcount = -1;
299                         return RED_DONT_MARK;
300
301                 case RED_BETWEEN_TRESH:
302                         if (++p->qcount) {
303                                 if (red_mark_probability(p, qavg)) {
304                                         p->qcount = 0;
305                                         p->qR = red_random(p);
306                                         return RED_PROB_MARK;
307                                 }
308                         } else
309                                 p->qR = red_random(p);
310
311                         return RED_DONT_MARK;
312
313                 case RED_ABOVE_MAX_TRESH:
314                         p->qcount = -1;
315                         return RED_HARD_MARK;
316         }
317
318         BUG();
319         return RED_DONT_MARK;
320 }
321
322 #endif