--- /dev/null
+/*
+ * Copyright 2002-2005, Instant802 Networks, Inc.
+ * Copyright 2005, Devicescape Software, Inc.
+ * Copyright 2007, Mattias Nissler <mattias.nissler@gmx.de>
+ *
+ * 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
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/netdevice.h>
+#include <linux/types.h>
+#include <linux/skbuff.h>
+
+#include <net/mac80211.h>
+#include "ieee80211_rate.h"
+
+
+/* This is an implementation of a TX rate control algorithm that uses a PID
+ * controller. Given a target failed frames rate, the controller decides about
+ * TX rate changes to meet the target failed frames rate.
+ *
+ * The controller basically computes the following:
+ *
+ * adj = CP * err + CI * err_avg + CD * (err - last_err)
+ *
+ * where
+ * adj adjustment value that is used to switch TX rate (see below)
+ * err current error: target vs. current failed frames percentage
+ * last_err last error
+ * err_avg average (i.e. poor man's integral) of recent errors
+ * CP Proportional coefficient
+ * CI Integral coefficient
+ * CD Derivative coefficient
+ *
+ * CP, CI, CD are subject to careful tuning.
+ *
+ * The integral component uses a exponential moving average approach instead of
+ * an actual sliding window. The 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).
+ *
+ * Note that for the computations we use a fixed-point representation to avoid
+ * floating point arithmetic. Hence, all values are shifted left by
+ * RC_PID_ARITH_SHIFT.
+ */
+
+/* Sampling period for measuring percentage of failed frames. */
+#define RC_PID_INTERVAL (HZ / 8)
+
+/* Exponential averaging smoothness (used for I part of PID controller) */
+#define RC_PID_SMOOTHING_SHIFT 3
+#define RC_PID_SMOOTHING (1 << RC_PID_SMOOTHING_SHIFT)
+
+/* Fixed point arithmetic shifting amount. */
+#define RC_PID_ARITH_SHIFT 8
+
+/* Fixed point arithmetic factor. */
+#define RC_PID_ARITH_FACTOR (1 << RC_PID_ARITH_SHIFT)
+
+/* Proportional PID component coefficient. */
+#define RC_PID_COEFF_P 15
+/* Integral PID component coefficient. */
+#define RC_PID_COEFF_I 9
+/* Derivative PID component coefficient. */
+#define RC_PID_COEFF_D 15
+
+/* Target failed frames rate for the PID controller. NB: This effectively gives
+ * maximum failed frames percentage we're willing to accept. If the wireless
+ * link quality is good, the controller will fail to adjust failed frames
+ * percentage to the target. This is intentional.
+ */
+#define RC_PID_TARGET_PF (11 << RC_PID_ARITH_SHIFT)
+
+struct rc_pid_sta_info {
+ unsigned long last_change;
+ unsigned long last_sample;
+
+ u32 tx_num_failed;
+ u32 tx_num_xmit;
+
+ /* Average failed frames percentage error (i.e. actual vs. target
+ * percentage), scaled by RC_PID_SMOOTHING. This value is computed
+ * using using an exponential weighted average technique:
+ *
+ * (RC_PID_SMOOTHING - 1) * err_avg_old + err
+ * err_avg = ------------------------------------------
+ * RC_PID_SMOOTHING
+ *
+ * where err_avg is the new approximation, err_avg_old the previous one
+ * and err is the error w.r.t. to the current failed frames percentage
+ * sample. Note that the bigger RC_PID_SMOOTHING the more weight is
+ * given to the previous estimate, resulting in smoother behavior (i.e.
+ * corresponding to a longer integration window).
+ *
+ * For computation, we actually don't use the above formula, but this
+ * one:
+ *
+ * err_avg_scaled = err_avg_old_scaled - err_avg_old + err
+ *
+ * where:
+ * err_avg_scaled = err * RC_PID_SMOOTHING
+ * err_avg_old_scaled = err_avg_old * RC_PID_SMOOTHING
+ *
+ * This avoids floating point numbers and the per_failed_old value can
+ * easily be obtained by shifting per_failed_old_scaled right by
+ * RC_PID_SMOOTHING_SHIFT.
+ */
+ s32 err_avg_sc;
+
+ /* Last framed failes percentage sample */
+ u32 last_pf;
+};
+
+/* Algorithm parameters. We keep them on a per-algorithm approach, so they can
+ * be tuned individually for each interface.
+ */
+struct rc_pid_info {
+
+ /* The failed frames percentage target. */
+ u32 target;
+
+ /* P, I and D coefficients. */
+ s32 coeff_p;
+ s32 coeff_i;
+ s32 coeff_d;
+};
+
+
+static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
+ struct sta_info *sta, int adj)
+{
+ struct ieee80211_sub_if_data *sdata;
+ struct ieee80211_hw_mode *mode;
+ int newidx = sta->txrate + adj;
+ int maxrate;
+ int back = (adj > 0) ? 1 : -1;
+
+ sdata = IEEE80211_DEV_TO_SUB_IF(sta->dev);
+ if (sdata->bss && sdata->bss->force_unicast_rateidx > -1) {
+ /* forced unicast rate - do not change STA rate */
+ return;
+ }
+
+ 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;
+
+ while (newidx != sta->txrate) {
+ if (rate_supported(sta, mode, newidx) &&
+ (maxrate < 0 || newidx <= maxrate)) {
+ sta->txrate = newidx;
+ break;
+ }
+
+ newidx += back;
+ }
+}
+
+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;
+ u32 pf;
+ s32 err_avg;
+ s32 err_prop;
+ s32 err_int;
+ s32 err_der;
+ int adj;
+
+ spinfo = sta->rate_ctrl_priv;
+ spinfo->last_sample = jiffies;
+
+ /* If no frames were transmitted, we assume the old sample is
+ * still a good measurement and copy it. */
+ if (spinfo->tx_num_xmit == 0)
+ pf = spinfo->last_pf;
+ else {
+ pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
+ pf <<= RC_PID_ARITH_SHIFT;
+
+ spinfo->tx_num_xmit = 0;
+ spinfo->tx_num_failed = 0;
+ }
+
+ /* Compute the proportional, integral and derivative errors. */
+ err_prop = RC_PID_TARGET_PF - pf;
+
+ err_avg = spinfo->err_avg_sc >> RC_PID_SMOOTHING_SHIFT;
+ spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
+ err_int = spinfo->err_avg_sc >> RC_PID_SMOOTHING_SHIFT;
+
+ err_der = pf - spinfo->last_pf;
+ spinfo->last_pf = pf;
+
+ /* 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);
+
+ /* Change rate. */
+ if (adj)
+ rate_control_pid_adjust_rate(local, sta, adj);
+}
+
+static void rate_control_pid_tx_status(void *priv, struct net_device *dev,
+ struct sk_buff *skb,
+ struct ieee80211_tx_status *status)
+{
+ struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
+ struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
+ struct rc_pid_info *pinfo = priv;
+ struct sta_info *sta;
+ struct rc_pid_sta_info *spinfo;
+
+ sta = sta_info_get(local, hdr->addr1);
+
+ if (!sta)
+ return;
+
+ /* Ignore all frames that were sent with a different rate than the rate
+ * we currently advise mac80211 to use. */
+ if (status->control.rate != &local->oper_hw_mode->rates[sta->txrate])
+ return;
+
+ spinfo = sta->rate_ctrl_priv;
+ spinfo->tx_num_xmit++;
+
+ /* We count frames that totally failed to be transmitted as two bad
+ * frames, those that made it out but had some retries as one good and
+ * one bad frame. */
+ if (status->excessive_retries) {
+ spinfo->tx_num_failed += 2;
+ spinfo->tx_num_xmit++;
+ } else if (status->retry_count) {
+ spinfo->tx_num_failed++;
+ spinfo->tx_num_xmit++;
+ }
+
+ if (status->excessive_retries) {
+ sta->tx_retry_failed++;
+ sta->tx_num_consecutive_failures++;
+ sta->tx_num_mpdu_fail++;
+ } else {
+ sta->last_ack_rssi[0] = sta->last_ack_rssi[1];
+ sta->last_ack_rssi[1] = sta->last_ack_rssi[2];
+ sta->last_ack_rssi[2] = status->ack_signal;
+ sta->tx_num_consecutive_failures = 0;
+ sta->tx_num_mpdu_ok++;
+ }
+ sta->tx_retry_count += status->retry_count;
+ sta->tx_num_mpdu_fail += status->retry_count;
+
+ /* Update PID controller state. */
+ if (time_after(jiffies, spinfo->last_sample + RC_PID_INTERVAL))
+ rate_control_pid_sample(pinfo, local, sta);
+
+ sta_info_put(sta);
+}
+
+static void rate_control_pid_get_rate(void *priv, struct net_device *dev,
+ struct ieee80211_hw_mode *mode,
+ struct sk_buff *skb,
+ struct rate_selection *sel)
+{
+ struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
+ struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
+ struct sta_info *sta;
+ int rateidx;
+
+ sta = sta_info_get(local, hdr->addr1);
+
+ if (!sta) {
+ sel->rate = rate_lowest(local, mode, NULL);
+ sta_info_put(sta);
+ return;
+ }
+
+ rateidx = sta->txrate;
+
+ if (rateidx >= mode->num_rates)
+ rateidx = mode->num_rates - 1;
+
+ sta_info_put(sta);
+
+ sel->rate = &mode->rates[rateidx];
+}
+
+static void rate_control_pid_rate_init(void *priv, void *priv_sta,
+ struct ieee80211_local *local,
+ struct sta_info *sta)
+{
+ /* TODO: This routine should consider using RSSI from previous packets
+ * as we need to have IEEE 802.1X auth succeed immediately after assoc..
+ * Until that method is implemented, we will use the lowest supported
+ * rate as a workaround. */
+ sta->txrate = rate_lowest_index(local, local->oper_hw_mode, sta);
+}
+
+static void *rate_control_pid_alloc(struct ieee80211_local *local)
+{
+ struct rc_pid_info *pinfo;
+
+ pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
+
+ 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;
+
+ return pinfo;
+}
+
+static void rate_control_pid_free(void *priv)
+{
+ struct rc_pid_info *pinfo = priv;
+ kfree(pinfo);
+}
+
+static void rate_control_pid_clear(void *priv)
+{
+}
+
+static void *rate_control_pid_alloc_sta(void *priv, gfp_t gfp)
+{
+ struct rc_pid_sta_info *spinfo;
+
+ spinfo = kzalloc(sizeof(*spinfo), gfp);
+
+ return spinfo;
+}
+
+static void rate_control_pid_free_sta(void *priv, void *priv_sta)
+{
+ struct rc_pid_sta_info *spinfo = priv_sta;
+ kfree(spinfo);
+}
+
+struct rate_control_ops mac80211_rcpid = {
+ .name = "pid",
+ .tx_status = rate_control_pid_tx_status,
+ .get_rate = rate_control_pid_get_rate,
+ .rate_init = rate_control_pid_rate_init,
+ .clear = rate_control_pid_clear,
+ .alloc = rate_control_pid_alloc,
+ .free = rate_control_pid_free,
+ .alloc_sta = rate_control_pid_alloc_sta,
+ .free_sta = rate_control_pid_free_sta,
+};
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