rc80211-pid: add rate behaviour learning algorithm
This patch introduces a learning algorithm in order for the PID controller to learn how to map adjustment values to rates. This is better described in code comments. Signed-off-by: Stefano Brivio <stefano.brivio@polimi.it> Signed-off-by: John W. Linville <linville@tuxdriver.com> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Stefano Brivio
David S. Miller
parent
c21b39aca4
commit
90d501d610
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@ -2,6 +2,7 @@
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* Copyright 2002-2005, Instant802 Networks, Inc.
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* Copyright 2005, Devicescape Software, Inc.
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* Copyright 2007, Mattias Nissler <mattias.nissler@gmx.de>
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* Copyright 2007, Stefano Brivio <stefano.brivio@polimi.it>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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@ -39,12 +40,18 @@
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* an actual sliding window. The advantage is that we don't need to keep an
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* array of the last N error values and computation is easier.
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*
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* Once we have the adj value, we need to map it to a TX rate to be selected.
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* For now, we depend on the rates to be ordered in a way such that more robust
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* rates (i.e. such that exhibit a lower framed failed percentage) come first.
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* E.g. for the 802.11b/g case, we first have the b rates in ascending order,
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* then the g rates. The adj simply decides the index of the TX rate in the list
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* to switch to (relative to the current TX rate entry).
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* Once we have the adj value, we map it to a rate by means of a learning
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* algorithm. This algorithm keeps the state of the percentual failed frames
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* difference between rates. The behaviour of the lowest available rate is kept
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* as a reference value, and every time we switch between two rates, we compute
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* the difference between the failed frames each rate exhibited. By doing so,
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* we compare behaviours which different rates exhibited in adjacent timeslices,
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* thus the comparison is minimally affected by external conditions. This
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* difference gets propagated to the whole set of measurements, so that the
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* reference is always the same. Periodically, we normalize this set so that
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* recent events weigh the most. By comparing the adj value with this set, we
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* avoid pejorative switches to lower rates and allow for switches to higher
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* rates if they behaved well.
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*
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* Note that for the computations we use a fixed-point representation to avoid
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* floating point arithmetic. Hence, all values are shifted left by
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@ -78,6 +85,16 @@
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*/
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#define RC_PID_TARGET_PF (11 << RC_PID_ARITH_SHIFT)
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/* Rate behaviour normalization quantity over time. */
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#define RC_PID_NORM_OFFSET 3
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/* Push high rates right after loading. */
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#define RC_PID_FAST_START 0
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/* Arithmetic right shift for positive and negative values for ISO C. */
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#define RC_PID_DO_ARITH_RIGHT_SHIFT(x, y) \
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(x) < 0 ? -((-(x)) >> (y)) : (x) >> (y)
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struct rc_pid_sta_info {
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unsigned long last_change;
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unsigned long last_sample;
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@ -121,6 +138,18 @@ struct rc_pid_sta_info {
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/* Algorithm parameters. We keep them on a per-algorithm approach, so they can
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* be tuned individually for each interface.
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*/
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struct rc_pid_rateinfo {
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/* Map sorted rates to rates in ieee80211_hw_mode. */
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int index;
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/* Map rates in ieee80211_hw_mode to sorted rates. */
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int rev_index;
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/* Comparison with the lowest rate. */
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int diff;
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};
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struct rc_pid_info {
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/* The failed frames percentage target. */
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@ -130,15 +159,56 @@ struct rc_pid_info {
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s32 coeff_p;
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s32 coeff_i;
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s32 coeff_d;
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/* Rates information. */
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struct rc_pid_rateinfo *rinfo;
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/* Index of the last used rate. */
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int oldrate;
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};
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/* Shift the adjustment so that we won't switch to a lower rate if it exhibited
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* a worse failed frames behaviour and we'll choose the highest rate whose
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* failed frames behaviour is not worse than the one of the original rate
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* target. While at it, check that the adjustment is within the ranges. Then,
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* provide the new rate index. */
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static int rate_control_pid_shift_adjust(struct rc_pid_rateinfo *r,
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int adj, int cur, int l)
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{
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int i, j, k, tmp;
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if (cur + adj < 0)
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return 0;
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if (cur + adj >= l)
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return l - 1;
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i = r[cur + adj].rev_index;
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j = r[cur].rev_index;
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if (adj < 0) {
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tmp = i;
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for (k = j; k >= i; k--)
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if (r[k].diff <= r[j].diff)
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tmp = k;
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return r[tmp].index;
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} else if (adj > 0) {
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tmp = i;
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for (k = i + 1; k + i < l; k++)
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if (r[k].diff <= r[i].diff)
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tmp = k;
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return r[tmp].index;
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}
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return cur + adj;
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}
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static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
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struct sta_info *sta, int adj)
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struct sta_info *sta, int adj,
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struct rc_pid_rateinfo *rinfo)
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{
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struct ieee80211_sub_if_data *sdata;
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struct ieee80211_hw_mode *mode;
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int newidx = sta->txrate + adj;
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int newidx;
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int maxrate;
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int back = (adj > 0) ? 1 : -1;
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@ -151,10 +221,8 @@ static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
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mode = local->oper_hw_mode;
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maxrate = sdata->bss ? sdata->bss->max_ratectrl_rateidx : -1;
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if (newidx < 0)
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newidx = 0;
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else if (newidx >= mode->num_rates)
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newidx = mode->num_rates - 1;
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newidx = rate_control_pid_shift_adjust(rinfo, adj, sta->txrate,
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mode->num_rates);
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while (newidx != sta->txrate) {
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if (rate_supported(sta, mode, newidx) &&
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@ -167,18 +235,37 @@ static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
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}
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}
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/* Normalize the failed frames per-rate differences. */
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static void rate_control_pid_normalize(struct rc_pid_rateinfo *r, int l)
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{
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int i;
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if (r[0].diff > RC_PID_NORM_OFFSET)
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r[0].diff -= RC_PID_NORM_OFFSET;
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else if (r[0].diff < -RC_PID_NORM_OFFSET)
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r[0].diff += RC_PID_NORM_OFFSET;
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for (i = 0; i < l - 1; i++)
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if (r[i + 1].diff > r[i].diff + RC_PID_NORM_OFFSET)
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r[i + 1].diff -= RC_PID_NORM_OFFSET;
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else if (r[i + 1].diff <= r[i].diff)
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r[i + 1].diff += RC_PID_NORM_OFFSET;
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}
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static void rate_control_pid_sample(struct rc_pid_info *pinfo,
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struct ieee80211_local *local,
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struct sta_info *sta)
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{
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struct rc_pid_sta_info *spinfo = sta->rate_ctrl_priv;
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struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
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struct ieee80211_hw_mode *mode;
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u32 pf;
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s32 err_avg;
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s32 err_prop;
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s32 err_int;
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s32 err_der;
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int adj;
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int adj, i, j, tmp;
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mode = local->oper_hw_mode;
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spinfo = sta->rate_ctrl_priv;
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spinfo->last_sample = jiffies;
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@ -194,6 +281,20 @@ static void rate_control_pid_sample(struct rc_pid_info *pinfo,
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spinfo->tx_num_failed = 0;
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}
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/* If we just switched rate, update the rate behaviour info. */
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if (pinfo->oldrate != sta->txrate) {
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i = rinfo[pinfo->oldrate].rev_index;
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j = rinfo[sta->txrate].rev_index;
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tmp = (pf - spinfo->last_pf);
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tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);
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rinfo[j].diff = rinfo[i].diff + tmp;
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pinfo->oldrate = sta->txrate;
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}
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rate_control_pid_normalize(rinfo, mode->num_rates);
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/* Compute the proportional, integral and derivative errors. */
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err_prop = RC_PID_TARGET_PF - pf;
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@ -207,16 +308,11 @@ static void rate_control_pid_sample(struct rc_pid_info *pinfo,
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/* Compute the controller output. */
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adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
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+ err_der * pinfo->coeff_d);
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/* We need to do an arithmetic right shift. ISO C says this is
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* implementation defined for negative left operands. Hence, be
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* careful to get it right, also for negative values. */
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adj = (adj < 0) ? -((-adj) >> (2 * RC_PID_ARITH_SHIFT)) :
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adj >> (2 * RC_PID_ARITH_SHIFT);
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adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);
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/* Change rate. */
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if (adj)
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rate_control_pid_adjust_rate(local, sta, adj);
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rate_control_pid_adjust_rate(local, sta, adj, rinfo);
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}
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static void rate_control_pid_tx_status(void *priv, struct net_device *dev,
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@ -316,13 +412,57 @@ static void rate_control_pid_rate_init(void *priv, void *priv_sta,
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static void *rate_control_pid_alloc(struct ieee80211_local *local)
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{
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struct rc_pid_info *pinfo;
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struct rc_pid_rateinfo *rinfo;
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struct ieee80211_hw_mode *mode;
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int i, j, tmp;
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bool s;
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pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
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if (!pinfo)
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return NULL;
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/* We can safely assume that oper_hw_mode won't change unless we get
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* reinitialized. */
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mode = local->oper_hw_mode;
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rinfo = kmalloc(sizeof(*rinfo) * mode->num_rates, GFP_ATOMIC);
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if (!rinfo) {
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kfree(pinfo);
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return NULL;
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}
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/* Sort the rates. This is optimized for the most common case (i.e.
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* almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
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* mapping too. */
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for (i = 0; i < mode->num_rates; i++) {
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rinfo[i].index = i;
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rinfo[i].rev_index = i;
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if (RC_PID_FAST_START)
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rinfo[i].diff = 0;
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else
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rinfo[i].diff = i * RC_PID_NORM_OFFSET;
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}
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for (i = 1; i < mode->num_rates; i++) {
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s = 0;
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for (j = 0; j < mode->num_rates - i; j++)
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if (unlikely(mode->rates[rinfo[j].index].rate >
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mode->rates[rinfo[j + 1].index].rate)) {
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tmp = rinfo[j].index;
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rinfo[j].index = rinfo[j + 1].index;
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rinfo[j + 1].index = tmp;
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rinfo[rinfo[j].index].rev_index = j;
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rinfo[rinfo[j + 1].index].rev_index = j + 1;
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s = 1;
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}
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if (!s)
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break;
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}
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pinfo->target = RC_PID_TARGET_PF;
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pinfo->coeff_p = RC_PID_COEFF_P;
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pinfo->coeff_i = RC_PID_COEFF_I;
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pinfo->coeff_d = RC_PID_COEFF_D;
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pinfo->rinfo = rinfo;
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pinfo->oldrate = 0;
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return pinfo;
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}
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@ -330,6 +470,7 @@ static void *rate_control_pid_alloc(struct ieee80211_local *local)
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static void rate_control_pid_free(void *priv)
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{
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struct rc_pid_info *pinfo = priv;
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kfree(pinfo->rinfo);
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kfree(pinfo);
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}
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