mac80211: add max lossless throughput per rate

[deliverable/linux.git] / net / mac80211 / rc80211_minstrel.c

/*
 * Copyright (C) 2008 Felix Fietkau <nbd@openwrt.org>
 *
 * 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.
 *
 * Based on minstrel.c:
 *   Copyright (C) 2005-2007 Derek Smithies <derek@indranet.co.nz>
 *   Sponsored by Indranet Technologies Ltd
 *
 * Based on sample.c:
 *   Copyright (c) 2005 John Bicket
 *   All rights reserved.
 *
 *   Redistribution and use in source and binary forms, with or without
 *   modification, are permitted provided that the following conditions
 *   are met:
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer,
 *      without modification.
 *   2. Redistributions in binary form must reproduce at minimum a disclaimer
 *      similar to the "NO WARRANTY" disclaimer below ("Disclaimer") and any
 *      redistribution must be conditioned upon including a substantially
 *      similar Disclaimer requirement for further binary redistribution.
 *   3. Neither the names of the above-listed copyright holders nor the names
 *      of any contributors may be used to endorse or promote products derived
 *      from this software without specific prior written permission.
 *
 *   Alternatively, this software may be distributed under the terms of the
 *   GNU General Public License ("GPL") version 2 as published by the Free
 *   Software Foundation.
 *
 *   NO WARRANTY
 *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 *   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 *   LIMITED TO, THE IMPLIED WARRANTIES OF NONINFRINGEMENT, MERCHANTIBILITY
 *   AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
 *   THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY,
 *   OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 *   SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 *   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
 *   IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 *   ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 *   THE POSSIBILITY OF SUCH DAMAGES.
 */
#include <linux/netdevice.h>
#include <linux/types.h>
#include <linux/skbuff.h>
#include <linux/debugfs.h>
#include <linux/random.h>
#include <linux/ieee80211.h>
#include <linux/slab.h>
#include <net/mac80211.h>
#include "rate.h"
#include "rc80211_minstrel.h"

#define SAMPLE_TBL(_mi, _idx, _col) \
                _mi->sample_table[(_idx * SAMPLE_COLUMNS) + _col]

/* convert mac80211 rate index to local array index */
static inline int
rix_to_ndx(struct minstrel_sta_info *mi, int rix)
{
        int i = rix;
        for (i = rix; i >= 0; i--)
                if (mi->r[i].rix == rix)
                        break;
        return i;
}

/* return current EMWA throughput */
int minstrel_get_tp_avg(struct minstrel_rate *mr, int prob_ewma)
{
        int usecs;

        usecs = mr->perfect_tx_time;
        if (!usecs)
                usecs = 1000000;

        /* reset thr. below 10% success */
        if (mr->stats.prob_ewma < MINSTREL_FRAC(10, 100))
                return 0;

        if (prob_ewma > MINSTREL_FRAC(90, 100))
                return MINSTREL_TRUNC(100000 * (MINSTREL_FRAC(90, 100) / usecs));
        else
                return MINSTREL_TRUNC(100000 * (prob_ewma / usecs));
}

/* find & sort topmost throughput rates */
static inline void
minstrel_sort_best_tp_rates(struct minstrel_sta_info *mi, int i, u8 *tp_list)
{
        int j = MAX_THR_RATES;
        struct minstrel_rate_stats *tmp_mrs = &mi->r[j - 1].stats;
        struct minstrel_rate_stats *cur_mrs = &mi->r[i].stats;

        while (j > 0 && (minstrel_get_tp_avg(&mi->r[i], cur_mrs->prob_ewma) >
               minstrel_get_tp_avg(&mi->r[tp_list[j - 1]], tmp_mrs->prob_ewma))) {
                j--;
                tmp_mrs = &mi->r[tp_list[j - 1]].stats;
        }

        if (j < MAX_THR_RATES - 1)
                memmove(&tp_list[j + 1], &tp_list[j], MAX_THR_RATES - (j + 1));
        if (j < MAX_THR_RATES)
                tp_list[j] = i;
}

static void
minstrel_set_rate(struct minstrel_sta_info *mi, struct ieee80211_sta_rates *ratetbl,
                  int offset, int idx)
{
        struct minstrel_rate *r = &mi->r[idx];

        ratetbl->rate[offset].idx = r->rix;
        ratetbl->rate[offset].count = r->adjusted_retry_count;
        ratetbl->rate[offset].count_cts = r->retry_count_cts;
        ratetbl->rate[offset].count_rts = r->stats.retry_count_rtscts;
}

static void
minstrel_update_rates(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
{
        struct ieee80211_sta_rates *ratetbl;
        int i = 0;

        ratetbl = kzalloc(sizeof(*ratetbl), GFP_ATOMIC);
        if (!ratetbl)
                return;

        /* Start with max_tp_rate */
        minstrel_set_rate(mi, ratetbl, i++, mi->max_tp_rate[0]);

        if (mp->hw->max_rates >= 3) {
                /* At least 3 tx rates supported, use max_tp_rate2 next */
                minstrel_set_rate(mi, ratetbl, i++, mi->max_tp_rate[1]);
        }

        if (mp->hw->max_rates >= 2) {
                /* At least 2 tx rates supported, use max_prob_rate next */
                minstrel_set_rate(mi, ratetbl, i++, mi->max_prob_rate);
        }

        /* Use lowest rate last */
        ratetbl->rate[i].idx = mi->lowest_rix;
        ratetbl->rate[i].count = mp->max_retry;
        ratetbl->rate[i].count_cts = mp->max_retry;
        ratetbl->rate[i].count_rts = mp->max_retry;

        rate_control_set_rates(mp->hw, mi->sta, ratetbl);
}

/*
* Recalculate success probabilities and counters for a given rate using EWMA
*/
void
minstrel_calc_rate_stats(struct minstrel_rate_stats *mrs)
{
        if (unlikely(mrs->attempts > 0)) {
                mrs->sample_skipped = 0;
                mrs->cur_prob = MINSTREL_FRAC(mrs->success, mrs->attempts);
                if (unlikely(!mrs->att_hist))
                        mrs->prob_ewma = mrs->cur_prob;
                else
                        mrs->prob_ewma = minstrel_ewma(mrs->prob_ewma,
                                                     mrs->cur_prob, EWMA_LEVEL);
                mrs->att_hist += mrs->attempts;
                mrs->succ_hist += mrs->success;
        } else {
                mrs->sample_skipped++;
        }

        mrs->last_success = mrs->success;
        mrs->last_attempts = mrs->attempts;
        mrs->success = 0;
        mrs->attempts = 0;
}

static void
minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
{
        u8 tmp_tp_rate[MAX_THR_RATES];
        u8 tmp_prob_rate = 0;
        int i, tmp_cur_tp, tmp_prob_tp;

        for (i = 0; i < MAX_THR_RATES; i++)
            tmp_tp_rate[i] = 0;

        for (i = 0; i < mi->n_rates; i++) {
                struct minstrel_rate *mr = &mi->r[i];
                struct minstrel_rate_stats *mrs = &mi->r[i].stats;
                struct minstrel_rate_stats *tmp_mrs = &mi->r[tmp_prob_rate].stats;

                /* Update success probabilities per rate */
                minstrel_calc_rate_stats(mrs);

                /* Sample less often below the 10% chance of success.
                 * Sample less often above the 95% chance of success. */
                if (mrs->prob_ewma > MINSTREL_FRAC(95, 100) ||
                    mrs->prob_ewma < MINSTREL_FRAC(10, 100)) {
                        mr->adjusted_retry_count = mrs->retry_count >> 1;
                        if (mr->adjusted_retry_count > 2)
                                mr->adjusted_retry_count = 2;
                        mr->sample_limit = 4;
                } else {
                        mr->sample_limit = -1;
                        mr->adjusted_retry_count = mrs->retry_count;
                }
                if (!mr->adjusted_retry_count)
                        mr->adjusted_retry_count = 2;

                minstrel_sort_best_tp_rates(mi, i, tmp_tp_rate);

                /* To determine the most robust rate (max_prob_rate) used at
                 * 3rd mmr stage we distinct between two cases:
                 * (1) if any success probabilitiy >= 95%, out of those rates
                 * choose the maximum throughput rate as max_prob_rate
                 * (2) if all success probabilities < 95%, the rate with
                 * highest success probability is chosen as max_prob_rate */
                if (mrs->prob_ewma >= MINSTREL_FRAC(95, 100)) {
                        tmp_cur_tp = minstrel_get_tp_avg(mr, mrs->prob_ewma);
                        tmp_prob_tp = minstrel_get_tp_avg(&mi->r[tmp_prob_rate],
                                                          tmp_mrs->prob_ewma);
                        if (tmp_cur_tp >= tmp_prob_tp)
                                tmp_prob_rate = i;
                } else {
                        if (mrs->prob_ewma >= tmp_mrs->prob_ewma)
                                tmp_prob_rate = i;
                }
        }

        /* Assign the new rate set */
        memcpy(mi->max_tp_rate, tmp_tp_rate, sizeof(mi->max_tp_rate));
        mi->max_prob_rate = tmp_prob_rate;

#ifdef CONFIG_MAC80211_DEBUGFS
        /* use fixed index if set */
        if (mp->fixed_rate_idx != -1) {
                mi->max_tp_rate[0] = mp->fixed_rate_idx;
                mi->max_tp_rate[1] = mp->fixed_rate_idx;
                mi->max_prob_rate = mp->fixed_rate_idx;
        }
#endif

        /* Reset update timer */
        mi->last_stats_update = jiffies;

        minstrel_update_rates(mp, mi);
}

static void
minstrel_tx_status(void *priv, struct ieee80211_supported_band *sband,
                   struct ieee80211_sta *sta, void *priv_sta,
                   struct ieee80211_tx_info *info)
{
        struct minstrel_priv *mp = priv;
        struct minstrel_sta_info *mi = priv_sta;
        struct ieee80211_tx_rate *ar = info->status.rates;
        int i, ndx;
        int success;

        success = !!(info->flags & IEEE80211_TX_STAT_ACK);

        for (i = 0; i < IEEE80211_TX_MAX_RATES; i++) {
                if (ar[i].idx < 0)
                        break;

                ndx = rix_to_ndx(mi, ar[i].idx);
                if (ndx < 0)
                        continue;

                mi->r[ndx].stats.attempts += ar[i].count;

                if ((i != IEEE80211_TX_MAX_RATES - 1) && (ar[i + 1].idx < 0))
                        mi->r[ndx].stats.success += success;
        }

        if ((info->flags & IEEE80211_TX_CTL_RATE_CTRL_PROBE) && (i >= 0))
                mi->sample_packets++;

        if (mi->sample_deferred > 0)
                mi->sample_deferred--;

        if (time_after(jiffies, mi->last_stats_update +
                                (mp->update_interval * HZ) / 1000))
                minstrel_update_stats(mp, mi);
}


static inline unsigned int
minstrel_get_retry_count(struct minstrel_rate *mr,
                         struct ieee80211_tx_info *info)
{
        u8 retry = mr->adjusted_retry_count;

        if (info->control.use_rts)
                retry = max_t(u8, 2, min(mr->stats.retry_count_rtscts, retry));
        else if (info->control.use_cts_prot)
                retry = max_t(u8, 2, min(mr->retry_count_cts, retry));
        return retry;
}


static int
minstrel_get_next_sample(struct minstrel_sta_info *mi)
{
        unsigned int sample_ndx;
        sample_ndx = SAMPLE_TBL(mi, mi->sample_row, mi->sample_column);
        mi->sample_row++;
        if ((int) mi->sample_row >= mi->n_rates) {
                mi->sample_row = 0;
                mi->sample_column++;
                if (mi->sample_column >= SAMPLE_COLUMNS)
                        mi->sample_column = 0;
        }
        return sample_ndx;
}

static void
minstrel_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_tx_info *info = IEEE80211_SKB_CB(skb);
        struct minstrel_sta_info *mi = priv_sta;
        struct minstrel_priv *mp = priv;
        struct ieee80211_tx_rate *rate = &info->control.rates[0];
        struct minstrel_rate *msr, *mr;
        unsigned int ndx;
        bool mrr_capable;
        bool prev_sample;
        int delta;
        int sampling_ratio;

        /* management/no-ack frames do not use rate control */
        if (rate_control_send_low(sta, priv_sta, txrc))
                return;

        /* check multi-rate-retry capabilities & adjust lookaround_rate */
        mrr_capable = mp->has_mrr &&
                      !txrc->rts &&
                      !txrc->bss_conf->use_cts_prot;
        if (mrr_capable)
                sampling_ratio = mp->lookaround_rate_mrr;
        else
                sampling_ratio = mp->lookaround_rate;

        /* increase sum packet counter */
        mi->total_packets++;

#ifdef CONFIG_MAC80211_DEBUGFS
        if (mp->fixed_rate_idx != -1)
                return;
#endif

        delta = (mi->total_packets * sampling_ratio / 100) -
                        (mi->sample_packets + mi->sample_deferred / 2);

        /* delta < 0: no sampling required */
        prev_sample = mi->prev_sample;
        mi->prev_sample = false;
        if (delta < 0 || (!mrr_capable && prev_sample))
                return;

        if (mi->total_packets >= 10000) {
                mi->sample_deferred = 0;
                mi->sample_packets = 0;
                mi->total_packets = 0;
        } else if (delta > mi->n_rates * 2) {
                /* With multi-rate retry, not every planned sample
                 * attempt actually gets used, due to the way the retry
                 * chain is set up - [max_tp,sample,prob,lowest] for
                 * sample_rate < max_tp.
                 *
                 * If there's too much sampling backlog and the link
                 * starts getting worse, minstrel would start bursting
                 * out lots of sampling frames, which would result
                 * in a large throughput loss. */
                mi->sample_packets += (delta - mi->n_rates * 2);
        }

        /* get next random rate sample */
        ndx = minstrel_get_next_sample(mi);
        msr = &mi->r[ndx];
        mr = &mi->r[mi->max_tp_rate[0]];

        /* Decide if direct ( 1st mrr stage) or indirect (2nd mrr stage)
         * rate sampling method should be used.
         * Respect such rates that are not sampled for 20 interations.
         */
        if (mrr_capable &&
            msr->perfect_tx_time > mr->perfect_tx_time &&
            msr->stats.sample_skipped < 20) {
                /* Only use IEEE80211_TX_CTL_RATE_CTRL_PROBE to mark
                 * packets that have the sampling rate deferred to the
                 * second MRR stage. Increase the sample counter only
                 * if the deferred sample rate was actually used.
                 * Use the sample_deferred counter to make sure that
                 * the sampling is not done in large bursts */
                info->flags |= IEEE80211_TX_CTL_RATE_CTRL_PROBE;
                rate++;
                mi->sample_deferred++;
        } else {
                if (!msr->sample_limit)
                        return;

                mi->sample_packets++;
                if (msr->sample_limit > 0)
                        msr->sample_limit--;
        }

        /* If we're not using MRR and the sampling rate already
         * has a probability of >95%, we shouldn't be attempting
         * to use it, as this only wastes precious airtime */
        if (!mrr_capable &&
           (mi->r[ndx].stats.prob_ewma > MINSTREL_FRAC(95, 100)))
                return;

        mi->prev_sample = true;

        rate->idx = mi->r[ndx].rix;
        rate->count = minstrel_get_retry_count(&mi->r[ndx], info);
}


static void
calc_rate_durations(enum ieee80211_band band,
                    struct minstrel_rate *d,
                    struct ieee80211_rate *rate,
                    struct cfg80211_chan_def *chandef)
{
        int erp = !!(rate->flags & IEEE80211_RATE_ERP_G);
        int shift = ieee80211_chandef_get_shift(chandef);

        d->perfect_tx_time = ieee80211_frame_duration(band, 1200,
                        DIV_ROUND_UP(rate->bitrate, 1 << shift), erp, 1,
                        shift);
        d->ack_time = ieee80211_frame_duration(band, 10,
                        DIV_ROUND_UP(rate->bitrate, 1 << shift), erp, 1,
                        shift);
}

static void
init_sample_table(struct minstrel_sta_info *mi)
{
        unsigned int i, col, new_idx;
        u8 rnd[8];

        mi->sample_column = 0;
        mi->sample_row = 0;
        memset(mi->sample_table, 0xff, SAMPLE_COLUMNS * mi->n_rates);

        for (col = 0; col < SAMPLE_COLUMNS; col++) {
                prandom_bytes(rnd, sizeof(rnd));
                for (i = 0; i < mi->n_rates; i++) {
                        new_idx = (i + rnd[i & 7]) % mi->n_rates;
                        while (SAMPLE_TBL(mi, new_idx, col) != 0xff)
                                new_idx = (new_idx + 1) % mi->n_rates;

                        SAMPLE_TBL(mi, new_idx, col) = i;
                }
        }
}

static void
minstrel_rate_init(void *priv, struct ieee80211_supported_band *sband,
                   struct cfg80211_chan_def *chandef,
                   struct ieee80211_sta *sta, void *priv_sta)
{
        struct minstrel_sta_info *mi = priv_sta;
        struct minstrel_priv *mp = priv;
        struct ieee80211_rate *ctl_rate;
        unsigned int i, n = 0;
        unsigned int t_slot = 9; /* FIXME: get real slot time */
        u32 rate_flags;

        mi->sta = sta;
        mi->lowest_rix = rate_lowest_index(sband, sta);
        ctl_rate = &sband->bitrates[mi->lowest_rix];
        mi->sp_ack_dur = ieee80211_frame_duration(sband->band, 10,
                                ctl_rate->bitrate,
                                !!(ctl_rate->flags & IEEE80211_RATE_ERP_G), 1,
                                ieee80211_chandef_get_shift(chandef));

        rate_flags = ieee80211_chandef_rate_flags(&mp->hw->conf.chandef);
        memset(mi->max_tp_rate, 0, sizeof(mi->max_tp_rate));
        mi->max_prob_rate = 0;

        for (i = 0; i < sband->n_bitrates; i++) {
                struct minstrel_rate *mr = &mi->r[n];
                struct minstrel_rate_stats *mrs = &mi->r[n].stats;
                unsigned int tx_time = 0, tx_time_cts = 0, tx_time_rtscts = 0;
                unsigned int tx_time_single;
                unsigned int cw = mp->cw_min;
                int shift;

                if (!rate_supported(sta, sband->band, i))
                        continue;
                if ((rate_flags & sband->bitrates[i].flags) != rate_flags)
                        continue;

                n++;
                memset(mr, 0, sizeof(*mr));
                memset(mrs, 0, sizeof(*mrs));

                mr->rix = i;
                shift = ieee80211_chandef_get_shift(chandef);
                mr->bitrate = DIV_ROUND_UP(sband->bitrates[i].bitrate,
                                           (1 << shift) * 5);
                calc_rate_durations(sband->band, mr, &sband->bitrates[i],
                                    chandef);

                /* calculate maximum number of retransmissions before
                 * fallback (based on maximum segment size) */
                mr->sample_limit = -1;
                mrs->retry_count = 1;
                mr->retry_count_cts = 1;
                mrs->retry_count_rtscts = 1;
                tx_time = mr->perfect_tx_time + mi->sp_ack_dur;
                do {
                        /* add one retransmission */
                        tx_time_single = mr->ack_time + mr->perfect_tx_time;

                        /* contention window */
                        tx_time_single += (t_slot * cw) >> 1;
                        cw = min((cw << 1) | 1, mp->cw_max);

                        tx_time += tx_time_single;
                        tx_time_cts += tx_time_single + mi->sp_ack_dur;
                        tx_time_rtscts += tx_time_single + 2 * mi->sp_ack_dur;
                        if ((tx_time_cts < mp->segment_size) &&
                                (mr->retry_count_cts < mp->max_retry))
                                mr->retry_count_cts++;
                        if ((tx_time_rtscts < mp->segment_size) &&
                                (mrs->retry_count_rtscts < mp->max_retry))
                                mrs->retry_count_rtscts++;
                } while ((tx_time < mp->segment_size) &&
                                (++mr->stats.retry_count < mp->max_retry));
                mr->adjusted_retry_count = mrs->retry_count;
                if (!(sband->bitrates[i].flags & IEEE80211_RATE_ERP_G))
                        mr->retry_count_cts = mrs->retry_count;
        }

        for (i = n; i < sband->n_bitrates; i++) {
                struct minstrel_rate *mr = &mi->r[i];
                mr->rix = -1;
        }

        mi->n_rates = n;
        mi->last_stats_update = jiffies;

        init_sample_table(mi);
        minstrel_update_rates(mp, mi);
}

static void *
minstrel_alloc_sta(void *priv, struct ieee80211_sta *sta, gfp_t gfp)
{
        struct ieee80211_supported_band *sband;
        struct minstrel_sta_info *mi;
        struct minstrel_priv *mp = priv;
        struct ieee80211_hw *hw = mp->hw;
        int max_rates = 0;
        int i;

        mi = kzalloc(sizeof(struct minstrel_sta_info), gfp);
        if (!mi)
                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;
        }

        mi->r = kzalloc(sizeof(struct minstrel_rate) * max_rates, gfp);
        if (!mi->r)
                goto error;

        mi->sample_table = kmalloc(SAMPLE_COLUMNS * max_rates, gfp);
        if (!mi->sample_table)
                goto error1;

        mi->last_stats_update = jiffies;
        return mi;

error1:
        kfree(mi->r);
error:
        kfree(mi);
        return NULL;
}

static void
minstrel_free_sta(void *priv, struct ieee80211_sta *sta, void *priv_sta)
{
        struct minstrel_sta_info *mi = priv_sta;

        kfree(mi->sample_table);
        kfree(mi->r);
        kfree(mi);
}

static void
minstrel_init_cck_rates(struct minstrel_priv *mp)
{
        static const int bitrates[4] = { 10, 20, 55, 110 };
        struct ieee80211_supported_band *sband;
        u32 rate_flags = ieee80211_chandef_rate_flags(&mp->hw->conf.chandef);
        int i, j;

        sband = mp->hw->wiphy->bands[IEEE80211_BAND_2GHZ];
        if (!sband)
                return;

        for (i = 0, j = 0; i < sband->n_bitrates; i++) {
                struct ieee80211_rate *rate = &sband->bitrates[i];

                if (rate->flags & IEEE80211_RATE_ERP_G)
                        continue;

                if ((rate_flags & sband->bitrates[i].flags) != rate_flags)
                        continue;

                for (j = 0; j < ARRAY_SIZE(bitrates); j++) {
                        if (rate->bitrate != bitrates[j])
                                continue;

                        mp->cck_rates[j] = i;
                        break;
                }
        }
}

static void *
minstrel_alloc(struct ieee80211_hw *hw, struct dentry *debugfsdir)
{
        struct minstrel_priv *mp;

        mp = kzalloc(sizeof(struct minstrel_priv), GFP_ATOMIC);
        if (!mp)
                return NULL;

        /* contention window settings
         * Just an approximation. Using the per-queue values would complicate
         * the calculations and is probably unnecessary */
        mp->cw_min = 15;
        mp->cw_max = 1023;

        /* number of packets (in %) to use for sampling other rates
         * sample less often for non-mrr packets, because the overhead
         * is much higher than with mrr */
        mp->lookaround_rate = 5;
        mp->lookaround_rate_mrr = 10;

        /* maximum time that the hw is allowed to stay in one MRR segment */
        mp->segment_size = 6000;

        if (hw->max_rate_tries > 0)
                mp->max_retry = hw->max_rate_tries;
        else
                /* safe default, does not necessarily have to match hw properties */
                mp->max_retry = 7;

        if (hw->max_rates >= 4)
                mp->has_mrr = true;

        mp->hw = hw;
        mp->update_interval = 100;

#ifdef CONFIG_MAC80211_DEBUGFS
        mp->fixed_rate_idx = (u32) -1;
        mp->dbg_fixed_rate = debugfs_create_u32("fixed_rate_idx",
                        S_IRUGO | S_IWUGO, debugfsdir, &mp->fixed_rate_idx);
#endif

        minstrel_init_cck_rates(mp);

        return mp;
}

static void
minstrel_free(void *priv)
{
#ifdef CONFIG_MAC80211_DEBUGFS
        debugfs_remove(((struct minstrel_priv *)priv)->dbg_fixed_rate);
#endif
        kfree(priv);
}

static u32 minstrel_get_expected_throughput(void *priv_sta)
{
        struct minstrel_sta_info *mi = priv_sta;
        struct minstrel_rate_stats *tmp_mrs;
        int idx = mi->max_tp_rate[0];
        int tmp_cur_tp;

        /* convert pkt per sec in kbps (1200 is the average pkt size used for
         * computing cur_tp
         */
        tmp_mrs = &mi->r[idx].stats;
        tmp_cur_tp = minstrel_get_tp_avg(&mi->r[idx], tmp_mrs->prob_ewma);
        tmp_cur_tp = tmp_cur_tp * 1200 * 8 / 1024;

        return tmp_cur_tp;
}

const struct rate_control_ops mac80211_minstrel = {
        .name = "minstrel",
        .tx_status_noskb = minstrel_tx_status,
        .get_rate = minstrel_get_rate,
        .rate_init = minstrel_rate_init,
        .alloc = minstrel_alloc,
        .free = minstrel_free,
        .alloc_sta = minstrel_alloc_sta,
        .free_sta = minstrel_free_sta,
#ifdef CONFIG_MAC80211_DEBUGFS
        .add_sta_debugfs = minstrel_add_sta_debugfs,
        .remove_sta_debugfs = minstrel_remove_sta_debugfs,
#endif
        .get_expected_throughput = minstrel_get_expected_throughput,
};

int __init
rc80211_minstrel_init(void)
{
        return ieee80211_rate_control_register(&mac80211_minstrel);
}

void
rc80211_minstrel_exit(void)
{
        ieee80211_rate_control_unregister(&mac80211_minstrel);
}