mac80211: add PID controller based rate control algorithm

Add a new rate control algorithm based on a PID controller. It samples the
percentage of failed frames over time, feeds the result into the controller and
uses its output to control the TX rate.

Signed-off-by: Mattias Nissler <mattias.nissler@gmx.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 365 insertions, 0 deletions

diff --git a/net/mac80211/rc80211_pid.c b/net/mac80211/rc80211_pid.c
new file mode 100644
index 000000000000..b358824b5ac0
--- /dev/null
+++ b/net/mac80211/rc80211_pid.c
@@ -0,0 +1,365 @@
+/*
+ * 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,
+};