Mattias Nissler | ad01837 | 2007-12-19 01:25:57 +0100 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2002-2005, Instant802 Networks, Inc. |
| 3 | * Copyright 2005, Devicescape Software, Inc. |
| 4 | * Copyright 2007, Mattias Nissler <mattias.nissler@gmx.de> |
| 5 | * |
| 6 | * This program is free software; you can redistribute it and/or modify |
| 7 | * it under the terms of the GNU General Public License version 2 as |
| 8 | * published by the Free Software Foundation. |
| 9 | */ |
| 10 | |
| 11 | #include <linux/netdevice.h> |
| 12 | #include <linux/types.h> |
| 13 | #include <linux/skbuff.h> |
| 14 | |
| 15 | #include <net/mac80211.h> |
| 16 | #include "ieee80211_rate.h" |
| 17 | |
| 18 | |
| 19 | /* This is an implementation of a TX rate control algorithm that uses a PID |
| 20 | * controller. Given a target failed frames rate, the controller decides about |
| 21 | * TX rate changes to meet the target failed frames rate. |
| 22 | * |
| 23 | * The controller basically computes the following: |
| 24 | * |
| 25 | * adj = CP * err + CI * err_avg + CD * (err - last_err) |
| 26 | * |
| 27 | * where |
| 28 | * adj adjustment value that is used to switch TX rate (see below) |
| 29 | * err current error: target vs. current failed frames percentage |
| 30 | * last_err last error |
| 31 | * err_avg average (i.e. poor man's integral) of recent errors |
| 32 | * CP Proportional coefficient |
| 33 | * CI Integral coefficient |
| 34 | * CD Derivative coefficient |
| 35 | * |
| 36 | * CP, CI, CD are subject to careful tuning. |
| 37 | * |
| 38 | * The integral component uses a exponential moving average approach instead of |
| 39 | * an actual sliding window. The advantage is that we don't need to keep an |
| 40 | * array of the last N error values and computation is easier. |
| 41 | * |
| 42 | * Once we have the adj value, we need to map it to a TX rate to be selected. |
| 43 | * For now, we depend on the rates to be ordered in a way such that more robust |
| 44 | * rates (i.e. such that exhibit a lower framed failed percentage) come first. |
| 45 | * E.g. for the 802.11b/g case, we first have the b rates in ascending order, |
| 46 | * then the g rates. The adj simply decides the index of the TX rate in the list |
| 47 | * to switch to (relative to the current TX rate entry). |
| 48 | * |
| 49 | * Note that for the computations we use a fixed-point representation to avoid |
| 50 | * floating point arithmetic. Hence, all values are shifted left by |
| 51 | * RC_PID_ARITH_SHIFT. |
| 52 | */ |
| 53 | |
| 54 | /* Sampling period for measuring percentage of failed frames. */ |
| 55 | #define RC_PID_INTERVAL (HZ / 8) |
| 56 | |
| 57 | /* Exponential averaging smoothness (used for I part of PID controller) */ |
| 58 | #define RC_PID_SMOOTHING_SHIFT 3 |
| 59 | #define RC_PID_SMOOTHING (1 << RC_PID_SMOOTHING_SHIFT) |
| 60 | |
| 61 | /* Fixed point arithmetic shifting amount. */ |
| 62 | #define RC_PID_ARITH_SHIFT 8 |
| 63 | |
| 64 | /* Fixed point arithmetic factor. */ |
| 65 | #define RC_PID_ARITH_FACTOR (1 << RC_PID_ARITH_SHIFT) |
| 66 | |
| 67 | /* Proportional PID component coefficient. */ |
| 68 | #define RC_PID_COEFF_P 15 |
| 69 | /* Integral PID component coefficient. */ |
| 70 | #define RC_PID_COEFF_I 9 |
| 71 | /* Derivative PID component coefficient. */ |
| 72 | #define RC_PID_COEFF_D 15 |
| 73 | |
| 74 | /* Target failed frames rate for the PID controller. NB: This effectively gives |
| 75 | * maximum failed frames percentage we're willing to accept. If the wireless |
| 76 | * link quality is good, the controller will fail to adjust failed frames |
| 77 | * percentage to the target. This is intentional. |
| 78 | */ |
| 79 | #define RC_PID_TARGET_PF (11 << RC_PID_ARITH_SHIFT) |
| 80 | |
| 81 | struct rc_pid_sta_info { |
| 82 | unsigned long last_change; |
| 83 | unsigned long last_sample; |
| 84 | |
| 85 | u32 tx_num_failed; |
| 86 | u32 tx_num_xmit; |
| 87 | |
| 88 | /* Average failed frames percentage error (i.e. actual vs. target |
| 89 | * percentage), scaled by RC_PID_SMOOTHING. This value is computed |
| 90 | * using using an exponential weighted average technique: |
| 91 | * |
| 92 | * (RC_PID_SMOOTHING - 1) * err_avg_old + err |
| 93 | * err_avg = ------------------------------------------ |
| 94 | * RC_PID_SMOOTHING |
| 95 | * |
| 96 | * where err_avg is the new approximation, err_avg_old the previous one |
| 97 | * and err is the error w.r.t. to the current failed frames percentage |
| 98 | * sample. Note that the bigger RC_PID_SMOOTHING the more weight is |
| 99 | * given to the previous estimate, resulting in smoother behavior (i.e. |
| 100 | * corresponding to a longer integration window). |
| 101 | * |
| 102 | * For computation, we actually don't use the above formula, but this |
| 103 | * one: |
| 104 | * |
| 105 | * err_avg_scaled = err_avg_old_scaled - err_avg_old + err |
| 106 | * |
| 107 | * where: |
| 108 | * err_avg_scaled = err * RC_PID_SMOOTHING |
| 109 | * err_avg_old_scaled = err_avg_old * RC_PID_SMOOTHING |
| 110 | * |
| 111 | * This avoids floating point numbers and the per_failed_old value can |
| 112 | * easily be obtained by shifting per_failed_old_scaled right by |
| 113 | * RC_PID_SMOOTHING_SHIFT. |
| 114 | */ |
| 115 | s32 err_avg_sc; |
| 116 | |
| 117 | /* Last framed failes percentage sample */ |
| 118 | u32 last_pf; |
| 119 | }; |
| 120 | |
| 121 | /* Algorithm parameters. We keep them on a per-algorithm approach, so they can |
| 122 | * be tuned individually for each interface. |
| 123 | */ |
| 124 | struct rc_pid_info { |
| 125 | |
| 126 | /* The failed frames percentage target. */ |
| 127 | u32 target; |
| 128 | |
| 129 | /* P, I and D coefficients. */ |
| 130 | s32 coeff_p; |
| 131 | s32 coeff_i; |
| 132 | s32 coeff_d; |
| 133 | }; |
| 134 | |
| 135 | |
| 136 | static void rate_control_pid_adjust_rate(struct ieee80211_local *local, |
| 137 | struct sta_info *sta, int adj) |
| 138 | { |
| 139 | struct ieee80211_sub_if_data *sdata; |
| 140 | struct ieee80211_hw_mode *mode; |
| 141 | int newidx = sta->txrate + adj; |
| 142 | int maxrate; |
| 143 | int back = (adj > 0) ? 1 : -1; |
| 144 | |
| 145 | sdata = IEEE80211_DEV_TO_SUB_IF(sta->dev); |
| 146 | if (sdata->bss && sdata->bss->force_unicast_rateidx > -1) { |
| 147 | /* forced unicast rate - do not change STA rate */ |
| 148 | return; |
| 149 | } |
| 150 | |
| 151 | mode = local->oper_hw_mode; |
| 152 | maxrate = sdata->bss ? sdata->bss->max_ratectrl_rateidx : -1; |
| 153 | |
| 154 | if (newidx < 0) |
| 155 | newidx = 0; |
| 156 | else if (newidx >= mode->num_rates) |
| 157 | newidx = mode->num_rates - 1; |
| 158 | |
| 159 | while (newidx != sta->txrate) { |
| 160 | if (rate_supported(sta, mode, newidx) && |
| 161 | (maxrate < 0 || newidx <= maxrate)) { |
| 162 | sta->txrate = newidx; |
| 163 | break; |
| 164 | } |
| 165 | |
| 166 | newidx += back; |
| 167 | } |
| 168 | } |
| 169 | |
| 170 | static void rate_control_pid_sample(struct rc_pid_info *pinfo, |
| 171 | struct ieee80211_local *local, |
| 172 | struct sta_info *sta) |
| 173 | { |
| 174 | struct rc_pid_sta_info *spinfo = sta->rate_ctrl_priv; |
| 175 | u32 pf; |
| 176 | s32 err_avg; |
| 177 | s32 err_prop; |
| 178 | s32 err_int; |
| 179 | s32 err_der; |
| 180 | int adj; |
| 181 | |
| 182 | spinfo = sta->rate_ctrl_priv; |
| 183 | spinfo->last_sample = jiffies; |
| 184 | |
| 185 | /* If no frames were transmitted, we assume the old sample is |
| 186 | * still a good measurement and copy it. */ |
| 187 | if (spinfo->tx_num_xmit == 0) |
| 188 | pf = spinfo->last_pf; |
| 189 | else { |
| 190 | pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit; |
| 191 | pf <<= RC_PID_ARITH_SHIFT; |
| 192 | |
| 193 | spinfo->tx_num_xmit = 0; |
| 194 | spinfo->tx_num_failed = 0; |
| 195 | } |
| 196 | |
| 197 | /* Compute the proportional, integral and derivative errors. */ |
| 198 | err_prop = RC_PID_TARGET_PF - pf; |
| 199 | |
| 200 | err_avg = spinfo->err_avg_sc >> RC_PID_SMOOTHING_SHIFT; |
| 201 | spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop; |
| 202 | err_int = spinfo->err_avg_sc >> RC_PID_SMOOTHING_SHIFT; |
| 203 | |
| 204 | err_der = pf - spinfo->last_pf; |
| 205 | spinfo->last_pf = pf; |
| 206 | |
| 207 | /* Compute the controller output. */ |
| 208 | adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i |
| 209 | + err_der * pinfo->coeff_d); |
| 210 | |
| 211 | /* We need to do an arithmetic right shift. ISO C says this is |
| 212 | * implementation defined for negative left operands. Hence, be |
| 213 | * careful to get it right, also for negative values. */ |
| 214 | adj = (adj < 0) ? -((-adj) >> (2 * RC_PID_ARITH_SHIFT)) : |
| 215 | adj >> (2 * RC_PID_ARITH_SHIFT); |
| 216 | |
| 217 | /* Change rate. */ |
| 218 | if (adj) |
| 219 | rate_control_pid_adjust_rate(local, sta, adj); |
| 220 | } |
| 221 | |
| 222 | static void rate_control_pid_tx_status(void *priv, struct net_device *dev, |
| 223 | struct sk_buff *skb, |
| 224 | struct ieee80211_tx_status *status) |
| 225 | { |
| 226 | struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr); |
| 227 | struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data; |
| 228 | struct rc_pid_info *pinfo = priv; |
| 229 | struct sta_info *sta; |
| 230 | struct rc_pid_sta_info *spinfo; |
| 231 | |
| 232 | sta = sta_info_get(local, hdr->addr1); |
| 233 | |
| 234 | if (!sta) |
| 235 | return; |
| 236 | |
| 237 | /* Ignore all frames that were sent with a different rate than the rate |
| 238 | * we currently advise mac80211 to use. */ |
| 239 | if (status->control.rate != &local->oper_hw_mode->rates[sta->txrate]) |
| 240 | return; |
| 241 | |
| 242 | spinfo = sta->rate_ctrl_priv; |
| 243 | spinfo->tx_num_xmit++; |
| 244 | |
| 245 | /* We count frames that totally failed to be transmitted as two bad |
| 246 | * frames, those that made it out but had some retries as one good and |
| 247 | * one bad frame. */ |
| 248 | if (status->excessive_retries) { |
| 249 | spinfo->tx_num_failed += 2; |
| 250 | spinfo->tx_num_xmit++; |
| 251 | } else if (status->retry_count) { |
| 252 | spinfo->tx_num_failed++; |
| 253 | spinfo->tx_num_xmit++; |
| 254 | } |
| 255 | |
| 256 | if (status->excessive_retries) { |
| 257 | sta->tx_retry_failed++; |
| 258 | sta->tx_num_consecutive_failures++; |
| 259 | sta->tx_num_mpdu_fail++; |
| 260 | } else { |
| 261 | sta->last_ack_rssi[0] = sta->last_ack_rssi[1]; |
| 262 | sta->last_ack_rssi[1] = sta->last_ack_rssi[2]; |
| 263 | sta->last_ack_rssi[2] = status->ack_signal; |
| 264 | sta->tx_num_consecutive_failures = 0; |
| 265 | sta->tx_num_mpdu_ok++; |
| 266 | } |
| 267 | sta->tx_retry_count += status->retry_count; |
| 268 | sta->tx_num_mpdu_fail += status->retry_count; |
| 269 | |
| 270 | /* Update PID controller state. */ |
| 271 | if (time_after(jiffies, spinfo->last_sample + RC_PID_INTERVAL)) |
| 272 | rate_control_pid_sample(pinfo, local, sta); |
| 273 | |
| 274 | sta_info_put(sta); |
| 275 | } |
| 276 | |
| 277 | static void rate_control_pid_get_rate(void *priv, struct net_device *dev, |
| 278 | struct ieee80211_hw_mode *mode, |
| 279 | struct sk_buff *skb, |
| 280 | struct rate_selection *sel) |
| 281 | { |
| 282 | struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr); |
| 283 | struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data; |
| 284 | struct sta_info *sta; |
| 285 | int rateidx; |
| 286 | |
| 287 | sta = sta_info_get(local, hdr->addr1); |
| 288 | |
| 289 | if (!sta) { |
| 290 | sel->rate = rate_lowest(local, mode, NULL); |
| 291 | sta_info_put(sta); |
| 292 | return; |
| 293 | } |
| 294 | |
| 295 | rateidx = sta->txrate; |
| 296 | |
| 297 | if (rateidx >= mode->num_rates) |
| 298 | rateidx = mode->num_rates - 1; |
| 299 | |
| 300 | sta_info_put(sta); |
| 301 | |
| 302 | sel->rate = &mode->rates[rateidx]; |
| 303 | } |
| 304 | |
| 305 | static void rate_control_pid_rate_init(void *priv, void *priv_sta, |
| 306 | struct ieee80211_local *local, |
| 307 | struct sta_info *sta) |
| 308 | { |
| 309 | /* TODO: This routine should consider using RSSI from previous packets |
| 310 | * as we need to have IEEE 802.1X auth succeed immediately after assoc.. |
| 311 | * Until that method is implemented, we will use the lowest supported |
| 312 | * rate as a workaround. */ |
| 313 | sta->txrate = rate_lowest_index(local, local->oper_hw_mode, sta); |
| 314 | } |
| 315 | |
| 316 | static void *rate_control_pid_alloc(struct ieee80211_local *local) |
| 317 | { |
| 318 | struct rc_pid_info *pinfo; |
| 319 | |
| 320 | pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC); |
| 321 | |
| 322 | pinfo->target = RC_PID_TARGET_PF; |
| 323 | pinfo->coeff_p = RC_PID_COEFF_P; |
| 324 | pinfo->coeff_i = RC_PID_COEFF_I; |
| 325 | pinfo->coeff_d = RC_PID_COEFF_D; |
| 326 | |
| 327 | return pinfo; |
| 328 | } |
| 329 | |
| 330 | static void rate_control_pid_free(void *priv) |
| 331 | { |
| 332 | struct rc_pid_info *pinfo = priv; |
| 333 | kfree(pinfo); |
| 334 | } |
| 335 | |
| 336 | static void rate_control_pid_clear(void *priv) |
| 337 | { |
| 338 | } |
| 339 | |
| 340 | static void *rate_control_pid_alloc_sta(void *priv, gfp_t gfp) |
| 341 | { |
| 342 | struct rc_pid_sta_info *spinfo; |
| 343 | |
| 344 | spinfo = kzalloc(sizeof(*spinfo), gfp); |
| 345 | |
| 346 | return spinfo; |
| 347 | } |
| 348 | |
| 349 | static void rate_control_pid_free_sta(void *priv, void *priv_sta) |
| 350 | { |
| 351 | struct rc_pid_sta_info *spinfo = priv_sta; |
| 352 | kfree(spinfo); |
| 353 | } |
| 354 | |
| 355 | struct rate_control_ops mac80211_rcpid = { |
| 356 | .name = "pid", |
| 357 | .tx_status = rate_control_pid_tx_status, |
| 358 | .get_rate = rate_control_pid_get_rate, |
| 359 | .rate_init = rate_control_pid_rate_init, |
| 360 | .clear = rate_control_pid_clear, |
| 361 | .alloc = rate_control_pid_alloc, |
| 362 | .free = rate_control_pid_free, |
| 363 | .alloc_sta = rate_control_pid_alloc_sta, |
| 364 | .free_sta = rate_control_pid_free_sta, |
| 365 | }; |