On Mon, 2007-12-10 at 03:24 +0100, Stefano Brivio wrote:
> 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@xxxxxxxxx>
> Cc: Mattias Nissler <mattias.nissler@xxxxxx>
>
> ---
>
> Mattias,
> this series addresses some of your concerns and some stupid bugs I just
> noticed about. Thank you for your comments.
>
> ---
>
> Index: wireless-2.6/net/mac80211/rc80211_pid.c
> ===================================================================
> --- wireless-2.6.orig/net/mac80211/rc80211_pid.c
> +++ wireless-2.6/net/mac80211/rc80211_pid.c
> @@ -2,6 +2,7 @@
> * Copyright 2002-2005, Instant802 Networks, Inc.
> * Copyright 2005, Devicescape Software, Inc.
> * Copyright 2007, Mattias Nissler <mattias.nissler@xxxxxx>
> + * Copyright 2007, Stefano Brivio <stefano.brivio@xxxxxxxxx>
> *
> * This program is free software; you can redistribute it and/or modify
> * it under the terms of the GNU General Public License version 2 as
> @@ -39,12 +40,18 @@
> * an actual sliding window. Advantage is that we don't need to keep an array of
> * the last N error values and computation is easier.
> *
> - * Once we have the adj value, we need to map it to a TX rate to be selected.
> - * For now, we depend on the rates to be ordered in a way such that more robust
> - * rates (i.e. such that exhibit a lower framed failed percentage) come first.
> - * E.g. for the 802.11b/g case, we first have the b rates in ascending order,
> - * then the g rates. The adj simply decides the index of the TX rate in the list
> - * to switch to (relative to the current TX rate entry).
> + * Once we have the adj value, we map it to a rate by means of a learning
> + * algorithm. This algorithm keeps the state of the percentual failed frames
> + * difference between rates. The behaviour of the lowest available rate is kept
> + * as a reference value, and every time we switch between two rates, we compute
> + * the difference between the failed frames each rate exhibited. By doing so,
> + * we compare behaviours which different rates exhibited in adjacent timeslices,
> + * thus the comparison is minimally affected by external conditions. This
> + * difference gets propagated to the whole set of measurements, so that the
> + * reference is always the same. Periodically, we normalize this set so that
> + * recent events weigh the most. By comparing the adj value with this set, we
> + * avoid pejorative switches to lower rates and allow for switches to higher
> + * rates if they behaved well.
> *
> * Note that for the computations we use a fixed-point representation to avoid
> * floating point arithmetic. Hence, all values are shifted left by
> @@ -78,6 +85,16 @@
> */
> #define RC_PID_TARGET_PF (20 << RC_PID_ARITH_SHIFT)
>
> +/* Rate behaviour normalization quantity over time. */
> +#define RC_PID_NORM_OFFSET 3
> +
> +/* Push high rates right after loading. */
> +#define RC_PID_FAST_START 0
> +
> +/* Arithmetic right shift for positive and negative values for ISO C. */
> +#define RC_PID_DO_ARITH_RIGHT_SHIFT(x, y) \
> + (x) < 0 ? -((-(x))) >> (y) : (x) >> (y)
> +
> struct rc_pid_sta_info {
> unsigned long last_change;
> unsigned long last_sample;
> @@ -121,6 +138,18 @@ struct rc_pid_sta_info {
> /* Algorithm parameters. We keep them on a per-algorithm approach, so they can
> * be tuned individually for each interface.
> */
> +struct rc_pid_rateinfo {
> +
> + /* The rate index in ieee80211_hw_mode. */
> + int index;
> +
> + /* Did we do any measurement on this rate? */
> + bool valid;
> +
> + /* Comparison with the lowest rate. */
> + int diff;
> +};
> +
> struct rc_pid_info {
>
> /* The failed frames percentage target. */
> @@ -130,15 +159,69 @@ struct rc_pid_info {
> s32 coeff_p;
> s32 coeff_i;
> s32 coeff_d;
> +
> + /* Rates information. */
> + struct rc_pid_rateinfo *rinfo;
> +
> + /* Index of the last used rate. */
> + int oldrate;
> };
>
> +static inline int rate_control_pid_r_to_i(struct rc_pid_rateinfo *r, int rate,
> + int l)
> +{
> + int i;
> +
> + for (i = 0; i < l; i++)
> + if (r[i].index == rate)
> + break;
> +
> + return i;
> +}
Isn't the store-direct-rinfo-indices approach nicer? Why did you decide
for the index conversion function in favour of storing direct indices?
> +
> +/* Shift the adjustment so that we won't switch to a lower rate if it exhibited
> + * a worse failed frames behaviour and we'll choose the highest rate whose
> + * failed frames behaviour is not worse than the one of the original rate
> + * target. While at it, check that the adjustment is within the ranges. Then,
> + * provide the new rate index. */
> +static int rate_control_pid_shift_adjust(struct rc_pid_rateinfo *r,
> + int adj, int cur, int l)
> +{
> + int i, j, k, tmp;
> +
> + if (cur + adj < 0)
> + return 0;
> + if (cur + adj >= l)
> + return l - 1;
> +
> + i = rate_control_pid_r_to_i(r, cur + adj, l);
> + if (unlikely(!r[i].valid))
> + return cur + adj;
> + j = rate_control_pid_r_to_i(r, cur, l);
> +
> + if (adj < 0 && r[j].valid) {
> + tmp = i;
> + for (k = j; k >= i; k--)
> + if (r[k].valid && r[k].diff <= r[j].diff)
> + tmp = k;
> + return r[tmp].index;
> + } else if (adj > 0) {
> + tmp = i;
> + for (k = i + 1; k + i < l; k++)
> + if (r[k].valid && r[k].diff <= r[i].diff)
> + tmp = k;
> + return r[tmp].index;
> + }
> + return cur + adj;
> +}
>
> static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
> - struct sta_info *sta, int adj)
> + struct sta_info *sta, int adj,
> + struct rc_pid_rateinfo *rinfo)
> {
> struct ieee80211_sub_if_data *sdata;
> struct ieee80211_hw_mode *mode;
> - int newidx = sta->txrate + adj;
> + int newidx;
> int maxrate;
> int back = (adj > 0) ? 1 : -1;
>
> @@ -151,10 +234,8 @@ static void rate_control_pid_adjust_rate
> mode = local->oper_hw_mode;
> maxrate = sdata->bss ? sdata->bss->max_ratectrl_rateidx : -1;
>
> - if (newidx < 0)
> - newidx = 0;
> - else if (newidx >= mode->num_rates)
> - newidx = mode->num_rates - 1;
> + newidx = rate_control_pid_shift_adjust(rinfo, adj, sta->txrate,
> + mode->num_rates);
>
> while (newidx != sta->txrate) {
> if (rate_supported(sta, mode, newidx) &&
> @@ -167,18 +248,39 @@ static void rate_control_pid_adjust_rate
> }
> }
>
> +/* Normalize the failed frames per-rate differences. */
> +static void rate_control_pid_normalize(struct rc_pid_rateinfo *r, int l)
> +{
> + int i;
> +
> + if (r[0].diff > RC_PID_NORM_OFFSET)
> + r[0].diff -= RC_PID_NORM_OFFSET;
> + else if (r[0].diff < -RC_PID_NORM_OFFSET)
> + r[0].diff += RC_PID_NORM_OFFSET;
> + for (i = 0; i < l - 1; i++)
> + if (likely(r[i + 1].valid)) {
> + if (r[i + 1].diff > r[i].diff + RC_PID_NORM_OFFSET)
> + r[i + 1].diff -= RC_PID_NORM_OFFSET;
> + else if (r[i + 1].diff <= r[i].diff)
> + r[i + 1].diff += RC_PID_NORM_OFFSET;
> + }
> +}
> +
> static void rate_control_pid_sample(struct rc_pid_info *pinfo,
> struct ieee80211_local *local,
> struct sta_info *sta)
> {
> struct rc_pid_sta_info *spinfo = sta->rate_ctrl_priv;
> + struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
> + struct ieee80211_hw_mode *mode;
> u32 pf;
> s32 err_avg;
> s32 err_prop;
> s32 err_int;
> s32 err_der;
> - int adj;
> + int adj, i, j, tmp;
>
> + mode = local->oper_hw_mode;
> spinfo = sta->rate_ctrl_priv;
> spinfo->last_sample = jiffies;
>
> @@ -194,6 +296,24 @@ static void rate_control_pid_sample(stru
> spinfo->tx_num_failed = 0;
> }
>
> + /* If we just switched rate, update the rate behaviour info. */
> + if (pinfo->oldrate != sta->txrate) {
> +
> + i = rate_control_pid_r_to_i(rinfo, pinfo->oldrate,
> + mode->num_rates);
> + j = rate_control_pid_r_to_i(rinfo, sta->txrate,
> + mode->num_rates);
> + rinfo[j].valid = 1;
> +
> + tmp = (pf - spinfo->last_pf);
> + tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);
> +
> + rinfo[j].diff = rinfo[i].diff + tmp;
> + rinfo[j].valid = 1;
> + pinfo->oldrate = sta->txrate;
> + }
> + rate_control_pid_normalize(rinfo, mode->num_rates);
> +
> /* Compute the proportional, integral and derivative errors. */
> err_prop = RC_PID_TARGET_PF - pf;
>
> @@ -207,16 +327,11 @@ static void rate_control_pid_sample(stru
> /* Compute the controller output. */
> adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
> + err_der * pinfo->coeff_d);
> -
> - /* We need to do an arithmetic right shift. ISO C says this is
> - * implementation defined for negative left operands. Hence, be
> - * careful to get it right, also for negative values. */
> - adj = (adj < 0) ? -((-adj) >> (2 * RC_PID_ARITH_SHIFT)) :
> - adj >> (2 * RC_PID_ARITH_SHIFT);
> + adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);
>
> /* Change rate. */
> if (adj)
> - rate_control_pid_adjust_rate(local, sta, adj);
> + rate_control_pid_adjust_rate(local, sta, adj, rinfo);
> }
>
> static void rate_control_pid_tx_status(void *priv, struct net_device *dev,
> @@ -315,13 +430,55 @@ static void rate_control_pid_rate_init(v
> static void *rate_control_pid_alloc(struct ieee80211_local *local)
> {
> struct rc_pid_info *pinfo;
> + struct rc_pid_rateinfo *rinfo;
> + struct ieee80211_hw_mode *mode;
> + int i, j, tmp;
> + bool s;
>
> pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
> + if (!pinfo)
> + return NULL;
> +
> + mode = local->oper_hw_mode;
> + rinfo = kmalloc(sizeof(*rinfo) * mode->num_rates, GFP_ATOMIC);
> + if (!rinfo) {
> + kfree(pinfo);
> + return NULL;
> + }
> +
> + /* Sort the rates. This is optimized for the most common case (i.e.
> + * almost-sorted CCK+OFDM rates). */
> + for (i = 0; i < mode->num_rates; i++) {
> + rinfo[i].index = i;
> + if (RC_PID_FAST_START) {
> + rinfo[i].valid = 1;
> + rinfo[i].diff = 0;
> + } else
> + rinfo[i].valid = 0;
> + }
> + for (i = 1; i < mode->num_rates; i++) {
> + s = 0;
> + for (j = 0; j < mode->num_rates - i; j++)
> + if (unlikely(mode->rates[rinfo[j].index].rate >
> + mode->rates[rinfo[j + 1].index].rate)) {
> + tmp = rinfo[j].index;
> + rinfo[j].index = rinfo[j + 1].index;
> + rinfo[j + 1].index = tmp;
> + s = 1;
> + }
> + if (!s)
> + break;
> + }
> +
> + rinfo[0].diff = 0;
> + rinfo[0].valid = 1;
>
> pinfo->target = RC_PID_TARGET_PF;
> pinfo->coeff_p = RC_PID_COEFF_P;
> pinfo->coeff_i = RC_PID_COEFF_I;
> pinfo->coeff_d = RC_PID_COEFF_D;
> + pinfo->rinfo = rinfo;
> + pinfo->oldrate = 0;
>
> return pinfo;
> }
> @@ -330,6 +487,7 @@ static void *rate_control_pid_alloc(stru
> static void rate_control_pid_free(void *priv)
> {
> struct rc_pid_info *pinfo = priv;
> + kfree(pinfo->rinfo);
> kfree(pinfo);
> }
>
>
>
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