rc80211_pid_algo.c

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/*
 * Copyright 2002-2005, Instant802 Networks, Inc.
 * Copyright 2005, Devicescape Software, Inc.
 * Copyright 2007, Mattias Nissler <mattias.nissler@gmx.de>
 * Copyright 2007-2008, Stefano Brivio <stefano.brivio@polimi.it>
 *
 * 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 <linux/debugfs.h>
#include <linux/slab.h>
#include <net/mac80211.h>
#include "rate.h"
#include "mesh.h"
#include "rc80211_pid.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) * (1 + sharpening)
 *
 * 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
 *      sharpening      non-zero when fast response is needed (i.e. right after
 *                      association or no frames sent for a long time), heading
 *                      to zero over time
 *      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 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
 * RC_PID_ARITH_SHIFT.
 */


/* Adjust the rate while ensuring 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 new rate is valid. */
static void rate_control_pid_adjust_rate(struct ieee80211_supported_band *sband,
                                         struct ieee80211_sta *sta,
                                         struct rc_pid_sta_info *spinfo, int adj,
                                         struct rc_pid_rateinfo *rinfo)
{
        int cur_sorted, new_sorted, probe, tmp, n_bitrates, band;
        int cur = spinfo->txrate_idx;

        band = sband->band;
        n_bitrates = sband->n_bitrates;

        /* Map passed arguments to sorted values. */
        cur_sorted = rinfo[cur].rev_index;
        new_sorted = cur_sorted + adj;

        /* Check limits. */
        if (new_sorted < 0)
                new_sorted = rinfo[0].rev_index;
        else if (new_sorted >= n_bitrates)
                new_sorted = rinfo[n_bitrates - 1].rev_index;

        tmp = new_sorted;

        if (adj < 0) {
                /* Ensure that the rate decrease isn't disadvantageous. */
                for (probe = cur_sorted; probe >= new_sorted; probe--)
                        if (rinfo[probe].diff <= rinfo[cur_sorted].diff &&
                            rate_supported(sta, band, rinfo[probe].index))
                                tmp = probe;
        } else {
                /* Look for rate increase with zero (or below) cost. */
                for (probe = new_sorted + 1; probe < n_bitrates; probe++)
                        if (rinfo[probe].diff <= rinfo[new_sorted].diff &&
                            rate_supported(sta, band, rinfo[probe].index))
                                tmp = probe;
        }

        /* Fit the rate found to the nearest supported rate. */
        do {
                if (rate_supported(sta, band, rinfo[tmp].index)) {
                        spinfo->txrate_idx = rinfo[tmp].index;
                        break;
                }
                if (adj < 0)
                        tmp--;
                else
                        tmp++;
        } while (tmp < n_bitrates && tmp >= 0);

#ifdef CONFIG_MAC80211_DEBUGFS
        rate_control_pid_event_rate_change(&spinfo->events,
                spinfo->txrate_idx,
                sband->bitrates[spinfo->txrate_idx].bitrate);
#endif
}

/* Normalize the failed frames per-rate differences. */
static void rate_control_pid_normalize(struct rc_pid_info *pinfo, int l)
{
        int i, norm_offset = pinfo->norm_offset;
        struct rc_pid_rateinfo *r = pinfo->rinfo;

        if (r[0].diff > norm_offset)
                r[0].diff -= norm_offset;
        else if (r[0].diff < -norm_offset)
                r[0].diff += norm_offset;
        for (i = 0; i < l - 1; i++)
                if (r[i + 1].diff > r[i].diff + norm_offset)
                        r[i + 1].diff -= norm_offset;
                else if (r[i + 1].diff <= r[i].diff)
                        r[i + 1].diff += norm_offset;
}

static void rate_control_pid_sample(struct rc_pid_info *pinfo,
                                    struct ieee80211_supported_band *sband,
                                    struct ieee80211_sta *sta,
                                    struct rc_pid_sta_info *spinfo)
{
        struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
        u32 pf;
        s32 err_avg;
        u32 err_prop;
        u32 err_int;
        u32 err_der;
        int adj, i, j, tmp;
        unsigned long period;

        /* In case nothing happened during the previous control interval, turn
         * the sharpening factor on. */
        period = msecs_to_jiffies(pinfo->sampling_period);
        if (jiffies - spinfo->last_sample > 2 * period)
                spinfo->sharp_cnt = pinfo->sharpen_duration;

        spinfo->last_sample = jiffies;

        /* This should never happen, but in case, we assume the old sample is
         * still a good measurement and copy it. */
        if (unlikely(spinfo->tx_num_xmit == 0))
                pf = spinfo->last_pf;
        else
                pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;

        spinfo->tx_num_xmit = 0;
        spinfo->tx_num_failed = 0;

        /* If we just switched rate, update the rate behaviour info. */
        if (pinfo->oldrate != spinfo->txrate_idx) {

                i = rinfo[pinfo->oldrate].rev_index;
                j = rinfo[spinfo->txrate_idx].rev_index;

                tmp = (pf - spinfo->last_pf);
                tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);

                rinfo[j].diff = rinfo[i].diff + tmp;
                pinfo->oldrate = spinfo->txrate_idx;
        }
        rate_control_pid_normalize(pinfo, sband->n_bitrates);

        /* Compute the proportional, integral and derivative errors. */
        err_prop = (pinfo->target - pf) << RC_PID_ARITH_SHIFT;

        err_avg = spinfo->err_avg_sc >> pinfo->smoothing_shift;
        spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
        err_int = spinfo->err_avg_sc >> pinfo->smoothing_shift;

        err_der = (pf - spinfo->last_pf) *
                  (1 + pinfo->sharpen_factor * spinfo->sharp_cnt);
        spinfo->last_pf = pf;
        if (spinfo->sharp_cnt)
                        spinfo->sharp_cnt--;

#ifdef CONFIG_MAC80211_DEBUGFS
        rate_control_pid_event_pf_sample(&spinfo->events, pf, err_prop, err_int,
                                         err_der);
#endif

        /* Compute the controller output. */
        adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
              + err_der * pinfo->coeff_d);
        adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);

        /* Change rate. */
        if (adj)
                rate_control_pid_adjust_rate(sband, sta, spinfo, adj, rinfo);
}

static void rate_control_pid_tx_status(void *priv, struct ieee80211_supported_band *sband,
                                       struct ieee80211_sta *sta, void *priv_sta,
                                       struct sk_buff *skb)
{
        struct rc_pid_info *pinfo = priv;
        struct rc_pid_sta_info *spinfo = priv_sta;
        unsigned long period;
        struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);

        if (!spinfo)
                return;

        /* Ignore all frames that were sent with a different rate than the rate
         * we currently advise mac80211 to use. */
        if (info->status.rates[0].idx != spinfo->txrate_idx)
                return;

        spinfo->tx_num_xmit++;

#ifdef CONFIG_MAC80211_DEBUGFS
        rate_control_pid_event_tx_status(&spinfo->events, info);
#endif

        /* 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 (!(info->flags & IEEE80211_TX_STAT_ACK)) {
                spinfo->tx_num_failed += 2;
                spinfo->tx_num_xmit++;
        } else if (info->status.rates[0].count > 1) {
                spinfo->tx_num_failed++;
                spinfo->tx_num_xmit++;
        }

        /* Update PID controller state. */
        period = msecs_to_jiffies(pinfo->sampling_period);
        if (time_after(jiffies, spinfo->last_sample + period))
                rate_control_pid_sample(pinfo, sband, sta, spinfo);
}

static void
rate_control_pid_get_rate(void *priv, struct ieee80211_sta *sta,
                          void *priv_sta,
                          struct ieee80211_tx_rate_control *txrc)
{
        struct sk_buff *skb = txrc->skb;
        struct ieee80211_supported_band *sband = txrc->sband;
        struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
        struct rc_pid_sta_info *spinfo = priv_sta;
        int rateidx;

        if (txrc->rts)
                info->control.rates[0].count =
                        txrc->hw->conf.long_frame_max_tx_count;
        else
                info->control.rates[0].count =
                        txrc->hw->conf.short_frame_max_tx_count;

        /* Send management frames and NO_ACK data using lowest rate. */
        if (rate_control_send_low(sta, priv_sta, txrc))
                return;

        rateidx = spinfo->txrate_idx;

        if (rateidx >= sband->n_bitrates)
                rateidx = sband->n_bitrates - 1;

        info->control.rates[0].idx = rateidx;

#ifdef CONFIG_MAC80211_DEBUGFS
        rate_control_pid_event_tx_rate(&spinfo->events,
                rateidx, sband->bitrates[rateidx].bitrate);
#endif
}

static void
rate_control_pid_rate_init(void *priv, struct ieee80211_supported_band *sband,
                           struct ieee80211_sta *sta, void *priv_sta)
{
        struct rc_pid_sta_info *spinfo = priv_sta;
        struct rc_pid_info *pinfo = priv;
        struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
        int i, j, tmp;
        bool s;

        /* 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. */

        /* Sort the rates. This is optimized for the most common case (i.e.
         * almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
         * mapping too. */
        for (i = 0; i < sband->n_bitrates; i++) {
                rinfo[i].index = i;
                rinfo[i].rev_index = i;
                if (RC_PID_FAST_START)
                        rinfo[i].diff = 0;
                else
                        rinfo[i].diff = i * pinfo->norm_offset;
        }
        for (i = 1; i < sband->n_bitrates; i++) {
                s = false;
                for (j = 0; j < sband->n_bitrates - i; j++)
                        if (unlikely(sband->bitrates[rinfo[j].index].bitrate >
                                     sband->bitrates[rinfo[j + 1].index].bitrate)) {
                                tmp = rinfo[j].index;
                                rinfo[j].index = rinfo[j + 1].index;
                                rinfo[j + 1].index = tmp;
                                rinfo[rinfo[j].index].rev_index = j;
                                rinfo[rinfo[j + 1].index].rev_index = j + 1;
                                s = true;
                        }
                if (!s)
                        break;
        }

        spinfo->txrate_idx = rate_lowest_index(sband, sta);
}

static void *rate_control_pid_alloc(struct ieee80211_hw *hw,
                                    struct dentry *debugfsdir)
{
        struct rc_pid_info *pinfo;
        struct rc_pid_rateinfo *rinfo;
        struct ieee80211_supported_band *sband;
        int i, max_rates = 0;
#ifdef CONFIG_MAC80211_DEBUGFS
        struct rc_pid_debugfs_entries *de;
#endif

        pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
        if (!pinfo)
                return NULL;

        for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
                sband = hw->wiphy->bands[i];
                if (sband && sband->n_bitrates > max_rates)
                        max_rates = sband->n_bitrates;
        }

        rinfo = kmalloc(sizeof(*rinfo) * max_rates, GFP_ATOMIC);
        if (!rinfo) {
                kfree(pinfo);
                return NULL;
        }

        pinfo->target = RC_PID_TARGET_PF;
        pinfo->sampling_period = RC_PID_INTERVAL;
        pinfo->coeff_p = RC_PID_COEFF_P;
        pinfo->coeff_i = RC_PID_COEFF_I;
        pinfo->coeff_d = RC_PID_COEFF_D;
        pinfo->smoothing_shift = RC_PID_SMOOTHING_SHIFT;
        pinfo->sharpen_factor = RC_PID_SHARPENING_FACTOR;
        pinfo->sharpen_duration = RC_PID_SHARPENING_DURATION;
        pinfo->norm_offset = RC_PID_NORM_OFFSET;
        pinfo->rinfo = rinfo;
        pinfo->oldrate = 0;

#ifdef CONFIG_MAC80211_DEBUGFS
        de = &pinfo->dentries;
        de->target = debugfs_create_u32("target_pf", S_IRUSR | S_IWUSR,
                                        debugfsdir, &pinfo->target);
        de->sampling_period = debugfs_create_u32("sampling_period",
                                                 S_IRUSR | S_IWUSR, debugfsdir,
                                                 &pinfo->sampling_period);
        de->coeff_p = debugfs_create_u32("coeff_p", S_IRUSR | S_IWUSR,
                                         debugfsdir, (u32 *)&pinfo->coeff_p);
        de->coeff_i = debugfs_create_u32("coeff_i", S_IRUSR | S_IWUSR,
                                         debugfsdir, (u32 *)&pinfo->coeff_i);
        de->coeff_d = debugfs_create_u32("coeff_d", S_IRUSR | S_IWUSR,
                                         debugfsdir, (u32 *)&pinfo->coeff_d);
        de->smoothing_shift = debugfs_create_u32("smoothing_shift",
                                                 S_IRUSR | S_IWUSR, debugfsdir,
                                                 &pinfo->smoothing_shift);
        de->sharpen_factor = debugfs_create_u32("sharpen_factor",
                                               S_IRUSR | S_IWUSR, debugfsdir,
                                               &pinfo->sharpen_factor);
        de->sharpen_duration = debugfs_create_u32("sharpen_duration",
                                                  S_IRUSR | S_IWUSR, debugfsdir,
                                                  &pinfo->sharpen_duration);
        de->norm_offset = debugfs_create_u32("norm_offset",
                                             S_IRUSR | S_IWUSR, debugfsdir,
                                             &pinfo->norm_offset);
#endif

        return pinfo;
}

static void rate_control_pid_free(void *priv)
{
        struct rc_pid_info *pinfo = priv;
#ifdef CONFIG_MAC80211_DEBUGFS
        struct rc_pid_debugfs_entries *de = &pinfo->dentries;

        debugfs_remove(de->norm_offset);
        debugfs_remove(de->sharpen_duration);
        debugfs_remove(de->sharpen_factor);
        debugfs_remove(de->smoothing_shift);
        debugfs_remove(de->coeff_d);
        debugfs_remove(de->coeff_i);
        debugfs_remove(de->coeff_p);
        debugfs_remove(de->sampling_period);
        debugfs_remove(de->target);
#endif

        kfree(pinfo->rinfo);
        kfree(pinfo);
}

static void *rate_control_pid_alloc_sta(void *priv, struct ieee80211_sta *sta,
                                        gfp_t gfp)
{
        struct rc_pid_sta_info *spinfo;

        spinfo = kzalloc(sizeof(*spinfo), gfp);
        if (spinfo == NULL)
                return NULL;

        spinfo->last_sample = jiffies;

#ifdef CONFIG_MAC80211_DEBUGFS
        spin_lock_init(&spinfo->events.lock);
        init_waitqueue_head(&spinfo->events.waitqueue);
#endif

        return spinfo;
}

static void rate_control_pid_free_sta(void *priv, struct ieee80211_sta *sta,
                                      void *priv_sta)
{
        kfree(priv_sta);
}

static 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,
        .alloc = rate_control_pid_alloc,
        .free = rate_control_pid_free,
        .alloc_sta = rate_control_pid_alloc_sta,
        .free_sta = rate_control_pid_free_sta,
#ifdef CONFIG_MAC80211_DEBUGFS
        .add_sta_debugfs = rate_control_pid_add_sta_debugfs,
        .remove_sta_debugfs = rate_control_pid_remove_sta_debugfs,
#endif
};

int __init rc80211_pid_init(void)
{
        return ieee80211_rate_control_register(&mac80211_rcpid);
}

void rc80211_pid_exit(void)
{
        ieee80211_rate_control_unregister(&mac80211_rcpid);
}