rc80211_minstrel.c

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/*
 * 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_COLUMNS  10
#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;
}

static void
minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
{
        u32 max_tp = 0, index_max_tp = 0, index_max_tp2 = 0;
        u32 max_prob = 0, index_max_prob = 0;
        u32 usecs;
        u32 p;
        int i;

        mi->stats_update = jiffies;
        for (i = 0; i < mi->n_rates; i++) {
                struct minstrel_rate *mr = &mi->r[i];

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

                /* To avoid rounding issues, probabilities scale from 0 (0%)
                 * to 18000 (100%) */
                if (mr->attempts) {
                        p = (mr->success * 18000) / mr->attempts;
                        mr->succ_hist += mr->success;
                        mr->att_hist += mr->attempts;
                        mr->cur_prob = p;
                        p = ((p * (100 - mp->ewma_level)) + (mr->probability *
                                mp->ewma_level)) / 100;
                        mr->probability = p;
                        mr->cur_tp = p * (1000000 / usecs);
                }

                mr->last_success = mr->success;
                mr->last_attempts = mr->attempts;
                mr->success = 0;
                mr->attempts = 0;

                /* Sample less often below the 10% chance of success.
                 * Sample less often above the 95% chance of success. */
                if ((mr->probability > 17100) || (mr->probability < 1800)) {
                        mr->adjusted_retry_count = mr->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 = mr->retry_count;
                }
                if (!mr->adjusted_retry_count)
                        mr->adjusted_retry_count = 2;
        }

        for (i = 0; i < mi->n_rates; i++) {
                struct minstrel_rate *mr = &mi->r[i];
                if (max_tp < mr->cur_tp) {
                        index_max_tp = i;
                        max_tp = mr->cur_tp;
                }
                if (max_prob < mr->probability) {
                        index_max_prob = i;
                        max_prob = mr->probability;
                }
        }

        max_tp = 0;
        for (i = 0; i < mi->n_rates; i++) {
                struct minstrel_rate *mr = &mi->r[i];

                if (i == index_max_tp)
                        continue;

                if (max_tp < mr->cur_tp) {
                        index_max_tp2 = i;
                        max_tp = mr->cur_tp;
                }
        }
        mi->max_tp_rate = index_max_tp;
        mi->max_tp_rate2 = index_max_tp2;
        mi->max_prob_rate = index_max_prob;
}

static void
minstrel_tx_status(void *priv, struct ieee80211_supported_band *sband,
                   struct ieee80211_sta *sta, void *priv_sta,
                   struct sk_buff *skb)
{
        struct minstrel_sta_info *mi = priv_sta;
        struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
        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].attempts += ar[i].count;

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

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

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


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

        if (info->control.rates[0].flags & IEEE80211_TX_RC_USE_RTS_CTS)
                retry = max(2U, min(mr->retry_count_rtscts, retry));
        else if (info->control.rates[0].flags & IEEE80211_TX_RC_USE_CTS_PROTECT)
                retry = max(2U, 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_idx, mi->sample_column);
        mi->sample_idx++;
        if ((int) mi->sample_idx > (mi->n_rates - 2)) {
                mi->sample_idx = 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 *ar = info->control.rates;
        unsigned int ndx, sample_ndx = 0;
        bool mrr;
        bool sample_slower = false;
        bool sample = false;
        int i, delta;
        int mrr_ndx[3];
        int sample_rate;

        if (rate_control_send_low(sta, priv_sta, txrc))
                return;

        mrr = mp->has_mrr && !txrc->rts && !txrc->bss_conf->use_cts_prot;

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

        ndx = mi->max_tp_rate;

        if (mrr)
                sample_rate = mp->lookaround_rate_mrr;
        else
                sample_rate = mp->lookaround_rate;

        mi->packet_count++;
        delta = (mi->packet_count * sample_rate / 100) -
                        (mi->sample_count + mi->sample_deferred / 2);

        /* delta > 0: sampling required */
        if ((delta > 0) && (mrr || !mi->prev_sample)) {
                struct minstrel_rate *msr;
                if (mi->packet_count >= 10000) {
                        mi->sample_deferred = 0;
                        mi->sample_count = 0;
                        mi->packet_count = 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_count += (delta - mi->n_rates * 2);
                }

                sample_ndx = minstrel_get_next_sample(mi);
                msr = &mi->r[sample_ndx];
                sample = true;
                sample_slower = mrr && (msr->perfect_tx_time >
                        mi->r[ndx].perfect_tx_time);

                if (!sample_slower) {
                        if (msr->sample_limit != 0) {
                                ndx = sample_ndx;
                                mi->sample_count++;
                                if (msr->sample_limit > 0)
                                        msr->sample_limit--;
                        } else {
                                sample = false;
                        }
                } else {
                        /* 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;
                        mi->sample_deferred++;
                }
        }
        mi->prev_sample = sample;

        /* 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 && sample && (mi->r[ndx].probability > 17100))
                ndx = mi->max_tp_rate;

        ar[0].idx = mi->r[ndx].rix;
        ar[0].count = minstrel_get_retry_count(&mi->r[ndx], info);

        if (!mrr) {
                if (!sample)
                        ar[0].count = mp->max_retry;
                ar[1].idx = mi->lowest_rix;
                ar[1].count = mp->max_retry;
                return;
        }

        /* MRR setup */
        if (sample) {
                if (sample_slower)
                        mrr_ndx[0] = sample_ndx;
                else
                        mrr_ndx[0] = mi->max_tp_rate;
        } else {
                mrr_ndx[0] = mi->max_tp_rate2;
        }
        mrr_ndx[1] = mi->max_prob_rate;
        mrr_ndx[2] = 0;
        for (i = 1; i < 4; i++) {
                ar[i].idx = mi->r[mrr_ndx[i - 1]].rix;
                ar[i].count = mi->r[mrr_ndx[i - 1]].adjusted_retry_count;
        }
}


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

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

static void
init_sample_table(struct minstrel_sta_info *mi)
{
        unsigned int i, col, new_idx;
        unsigned int n_srates = mi->n_rates - 1;
        u8 rnd[8];

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

        for (col = 0; col < SAMPLE_COLUMNS; col++) {
                for (i = 0; i < n_srates; i++) {
                        get_random_bytes(rnd, sizeof(rnd));
                        new_idx = (i + rnd[i & 7]) % n_srates;

                        while (SAMPLE_TBL(mi, new_idx, col) != 0)
                                new_idx = (new_idx + 1) % n_srates;

                        /* Don't sample the slowest rate (i.e. slowest base
                         * rate). We must presume that the slowest rate works
                         * fine, or else other management frames will also be
                         * failing and the link will break */
                        SAMPLE_TBL(mi, new_idx, col) = i + 1;
                }
        }
}

static void
minstrel_rate_init(void *priv, struct ieee80211_supported_band *sband,
               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 */

        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);

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

                if (!rate_supported(sta, sband->band, i))
                        continue;
                n++;
                memset(mr, 0, sizeof(*mr));

                mr->rix = i;
                mr->bitrate = sband->bitrates[i].bitrate / 5;
                calc_rate_durations(sband->band, mr, &sband->bitrates[i]);

                /* calculate maximum number of retransmissions before
                 * fallback (based on maximum segment size) */
                mr->sample_limit = -1;
                mr->retry_count = 1;
                mr->retry_count_cts = 1;
                mr->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) &&
                                (mr->retry_count_rtscts < mp->max_retry))
                                mr->retry_count_rtscts++;
                } while ((tx_time < mp->segment_size) &&
                                (++mr->retry_count < mp->max_retry));
                mr->adjusted_retry_count = mr->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->stats_update = jiffies;

        init_sample_table(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->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_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;

        /* moving average weight for EWMA */
        mp->ewma_level = 75;

        /* 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

        return mp;
}

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

struct rate_control_ops mac80211_minstrel = {
        .name = "minstrel",
        .tx_status = 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
};

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

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