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linux/net/mac80211/rc80211_minstrel_ht.c
Felix Fietkau d66c258278 mac80211: minstrel_ht: fix rounding issue in MCS duration calculation 
On very high MCS bitrates, the calculated duration of rates that are
next to each other can be very imprecise, due to the small packet size
used as reference (1200 bytes).
This is most visible in VHT80 nss=2 MCS8/9, for which minstrel shows the
same throughput when the probability is also the same. This leads to a
bad rate selection for such rates.

Fix this issue by introducing an average A-MPDU size factor into the
calculation.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
2015-03-17 11:03:30 +01:00

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/*
* Copyright (C) 2010-2013 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.
*/
#include <linux/netdevice.h>
#include <linux/types.h>
#include <linux/skbuff.h>
#include <linux/debugfs.h>
#include <linux/random.h>
#include <linux/moduleparam.h>
#include <linux/ieee80211.h>
#include <net/mac80211.h>
#include "rate.h"
#include "rc80211_minstrel.h"
#include "rc80211_minstrel_ht.h"
#define AVG_AMPDU_SIZE 16
#define AVG_PKT_SIZE 1200
/* Number of bits for an average sized packet */
#define MCS_NBITS ((AVG_PKT_SIZE * AVG_AMPDU_SIZE) << 3)
/* Number of symbols for a packet with (bps) bits per symbol */
#define MCS_NSYMS(bps) DIV_ROUND_UP(MCS_NBITS, (bps))
/* Transmission time (nanoseconds) for a packet containing (syms) symbols */
#define MCS_SYMBOL_TIME(sgi, syms) \
(sgi ? \
((syms) * 18000 + 4000) / 5 : /* syms * 3.6 us */ \
((syms) * 1000) << 2 /* syms * 4 us */ \
)
/* Transmit duration for the raw data part of an average sized packet */
#define MCS_DURATION(streams, sgi, bps) \
(MCS_SYMBOL_TIME(sgi, MCS_NSYMS((streams) * (bps))) / AVG_AMPDU_SIZE)
#define BW_20 0
#define BW_40 1
#define BW_80 2
/*
* Define group sort order: HT40 -> SGI -> #streams
*/
#define GROUP_IDX(_streams, _sgi, _ht40) \
MINSTREL_HT_GROUP_0 + \
MINSTREL_MAX_STREAMS * 2 * _ht40 + \
MINSTREL_MAX_STREAMS * _sgi + \
_streams - 1
/* MCS rate information for an MCS group */
#define MCS_GROUP(_streams, _sgi, _ht40) \
[GROUP_IDX(_streams, _sgi, _ht40)] = { \
.streams = _streams, \
.flags = \
IEEE80211_TX_RC_MCS | \
(_sgi ? IEEE80211_TX_RC_SHORT_GI : 0) | \
(_ht40 ? IEEE80211_TX_RC_40_MHZ_WIDTH : 0), \
.duration = { \
MCS_DURATION(_streams, _sgi, _ht40 ? 54 : 26), \
MCS_DURATION(_streams, _sgi, _ht40 ? 108 : 52), \
MCS_DURATION(_streams, _sgi, _ht40 ? 162 : 78), \
MCS_DURATION(_streams, _sgi, _ht40 ? 216 : 104), \
MCS_DURATION(_streams, _sgi, _ht40 ? 324 : 156), \
MCS_DURATION(_streams, _sgi, _ht40 ? 432 : 208), \
MCS_DURATION(_streams, _sgi, _ht40 ? 486 : 234), \
MCS_DURATION(_streams, _sgi, _ht40 ? 540 : 260) \
} \
}
#define VHT_GROUP_IDX(_streams, _sgi, _bw) \
(MINSTREL_VHT_GROUP_0 + \
MINSTREL_MAX_STREAMS * 2 * (_bw) + \
MINSTREL_MAX_STREAMS * (_sgi) + \
(_streams) - 1)
#define BW2VBPS(_bw, r3, r2, r1) \
(_bw == BW_80 ? r3 : _bw == BW_40 ? r2 : r1)
#define VHT_GROUP(_streams, _sgi, _bw) \
[VHT_GROUP_IDX(_streams, _sgi, _bw)] = { \
.streams = _streams, \
.flags = \
IEEE80211_TX_RC_VHT_MCS | \
(_sgi ? IEEE80211_TX_RC_SHORT_GI : 0) | \
(_bw == BW_80 ? IEEE80211_TX_RC_80_MHZ_WIDTH : \
_bw == BW_40 ? IEEE80211_TX_RC_40_MHZ_WIDTH : 0), \
.duration = { \
MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 117, 54, 26)), \
MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 234, 108, 52)), \
MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 351, 162, 78)), \
MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 468, 216, 104)), \
MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 702, 324, 156)), \
MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 936, 432, 208)), \
MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 1053, 486, 234)), \
MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 1170, 540, 260)), \
MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 1404, 648, 312)), \
MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 1560, 720, 346)) \
} \
}
#define CCK_DURATION(_bitrate, _short, _len) \
(1000 * (10 /* SIFS */ + \
(_short ? 72 + 24 : 144 + 48) + \
(8 * (_len + 4) * 10) / (_bitrate)))
#define CCK_ACK_DURATION(_bitrate, _short) \
(CCK_DURATION((_bitrate > 10 ? 20 : 10), false, 60) + \
CCK_DURATION(_bitrate, _short, AVG_PKT_SIZE))
#define CCK_DURATION_LIST(_short) \
CCK_ACK_DURATION(10, _short), \
CCK_ACK_DURATION(20, _short), \
CCK_ACK_DURATION(55, _short), \
CCK_ACK_DURATION(110, _short)
#define CCK_GROUP \
[MINSTREL_CCK_GROUP] = { \
.streams = 0, \
.flags = 0, \
.duration = { \
CCK_DURATION_LIST(false), \
CCK_DURATION_LIST(true) \
} \
}
#ifdef CONFIG_MAC80211_RC_MINSTREL_VHT
static bool minstrel_vht_only = true;
module_param(minstrel_vht_only, bool, 0644);
MODULE_PARM_DESC(minstrel_vht_only,
"Use only VHT rates when VHT is supported by sta.");
#endif
/*
* To enable sufficiently targeted rate sampling, MCS rates are divided into
* groups, based on the number of streams and flags (HT40, SGI) that they
* use.
*
* Sortorder has to be fixed for GROUP_IDX macro to be applicable:
* BW -> SGI -> #streams
*/
const struct mcs_group minstrel_mcs_groups[] = {
MCS_GROUP(1, 0, BW_20),
MCS_GROUP(2, 0, BW_20),
#if MINSTREL_MAX_STREAMS >= 3
MCS_GROUP(3, 0, BW_20),
#endif
MCS_GROUP(1, 1, BW_20),
MCS_GROUP(2, 1, BW_20),
#if MINSTREL_MAX_STREAMS >= 3
MCS_GROUP(3, 1, BW_20),
#endif
MCS_GROUP(1, 0, BW_40),
MCS_GROUP(2, 0, BW_40),
#if MINSTREL_MAX_STREAMS >= 3
MCS_GROUP(3, 0, BW_40),
#endif
MCS_GROUP(1, 1, BW_40),
MCS_GROUP(2, 1, BW_40),
#if MINSTREL_MAX_STREAMS >= 3
MCS_GROUP(3, 1, BW_40),
#endif
CCK_GROUP,
#ifdef CONFIG_MAC80211_RC_MINSTREL_VHT
VHT_GROUP(1, 0, BW_20),
VHT_GROUP(2, 0, BW_20),
#if MINSTREL_MAX_STREAMS >= 3
VHT_GROUP(3, 0, BW_20),
#endif
VHT_GROUP(1, 1, BW_20),
VHT_GROUP(2, 1, BW_20),
#if MINSTREL_MAX_STREAMS >= 3
VHT_GROUP(3, 1, BW_20),
#endif
VHT_GROUP(1, 0, BW_40),
VHT_GROUP(2, 0, BW_40),
#if MINSTREL_MAX_STREAMS >= 3
VHT_GROUP(3, 0, BW_40),
#endif
VHT_GROUP(1, 1, BW_40),
VHT_GROUP(2, 1, BW_40),
#if MINSTREL_MAX_STREAMS >= 3
VHT_GROUP(3, 1, BW_40),
#endif
VHT_GROUP(1, 0, BW_80),
VHT_GROUP(2, 0, BW_80),
#if MINSTREL_MAX_STREAMS >= 3
VHT_GROUP(3, 0, BW_80),
#endif
VHT_GROUP(1, 1, BW_80),
VHT_GROUP(2, 1, BW_80),
#if MINSTREL_MAX_STREAMS >= 3
VHT_GROUP(3, 1, BW_80),
#endif
#endif
};
static u8 sample_table[SAMPLE_COLUMNS][MCS_GROUP_RATES] __read_mostly;
static void
minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi);
/*
* Some VHT MCSes are invalid (when Ndbps / Nes is not an integer)
* e.g for MCS9@20MHzx1Nss: Ndbps=8x52*(5/6) Nes=1
*
* Returns the valid mcs map for struct minstrel_mcs_group_data.supported
*/
static u16
minstrel_get_valid_vht_rates(int bw, int nss, __le16 mcs_map)
{
u16 mask = 0;
if (bw == BW_20) {
if (nss != 3 && nss != 6)
mask = BIT(9);
} else if (bw == BW_80) {
if (nss == 3 || nss == 7)
mask = BIT(6);
else if (nss == 6)
mask = BIT(9);
} else {
WARN_ON(bw != BW_40);
}
switch ((le16_to_cpu(mcs_map) >> (2 * (nss - 1))) & 3) {
case IEEE80211_VHT_MCS_SUPPORT_0_7:
mask |= 0x300;
break;
case IEEE80211_VHT_MCS_SUPPORT_0_8:
mask |= 0x200;
break;
case IEEE80211_VHT_MCS_SUPPORT_0_9:
break;
default:
mask = 0x3ff;
}
return 0x3ff & ~mask;
}
/*
* Look up an MCS group index based on mac80211 rate information
*/
static int
minstrel_ht_get_group_idx(struct ieee80211_tx_rate *rate)
{
return GROUP_IDX((rate->idx / 8) + 1,
!!(rate->flags & IEEE80211_TX_RC_SHORT_GI),
!!(rate->flags & IEEE80211_TX_RC_40_MHZ_WIDTH));
}
static int
minstrel_vht_get_group_idx(struct ieee80211_tx_rate *rate)
{
return VHT_GROUP_IDX(ieee80211_rate_get_vht_nss(rate),
!!(rate->flags & IEEE80211_TX_RC_SHORT_GI),
!!(rate->flags & IEEE80211_TX_RC_40_MHZ_WIDTH) +
2*!!(rate->flags & IEEE80211_TX_RC_80_MHZ_WIDTH));
}
static struct minstrel_rate_stats *
minstrel_ht_get_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
struct ieee80211_tx_rate *rate)
{
int group, idx;
if (rate->flags & IEEE80211_TX_RC_MCS) {
group = minstrel_ht_get_group_idx(rate);
idx = rate->idx % 8;
} else if (rate->flags & IEEE80211_TX_RC_VHT_MCS) {
group = minstrel_vht_get_group_idx(rate);
idx = ieee80211_rate_get_vht_mcs(rate);
} else {
group = MINSTREL_CCK_GROUP;
for (idx = 0; idx < ARRAY_SIZE(mp->cck_rates); idx++)
if (rate->idx == mp->cck_rates[idx])
break;
/* short preamble */
if (!(mi->groups[group].supported & BIT(idx)))
idx += 4;
}
return &mi->groups[group].rates[idx];
}
static inline struct minstrel_rate_stats *
minstrel_get_ratestats(struct minstrel_ht_sta *mi, int index)
{
return &mi->groups[index / MCS_GROUP_RATES].rates[index % MCS_GROUP_RATES];
}
/*
* Recalculate success probabilities and counters for a rate using EWMA
*/
static void
minstrel_calc_rate_ewma(struct minstrel_rate_stats *mr)
{
if (unlikely(mr->attempts > 0)) {
mr->sample_skipped = 0;
mr->cur_prob = MINSTREL_FRAC(mr->success, mr->attempts);
if (!mr->att_hist)
mr->probability = mr->cur_prob;
else
mr->probability = minstrel_ewma(mr->probability,
mr->cur_prob, EWMA_LEVEL);
mr->att_hist += mr->attempts;
mr->succ_hist += mr->success;
} else {
mr->sample_skipped++;
}
mr->last_success = mr->success;
mr->last_attempts = mr->attempts;
mr->success = 0;
mr->attempts = 0;
}
/*
* Calculate throughput based on the average A-MPDU length, taking into account
* the expected number of retransmissions and their expected length
*/
static void
minstrel_ht_calc_tp(struct minstrel_ht_sta *mi, int group, int rate)
{
struct minstrel_rate_stats *mr;
unsigned int nsecs = 0;
unsigned int tp;
unsigned int prob;
mr = &mi->groups[group].rates[rate];
prob = mr->probability;
if (prob < MINSTREL_FRAC(1, 10)) {
mr->cur_tp = 0;
return;
}
/*
* For the throughput calculation, limit the probability value to 90% to
* account for collision related packet error rate fluctuation
*/
if (prob > MINSTREL_FRAC(9, 10))
prob = MINSTREL_FRAC(9, 10);
if (group != MINSTREL_CCK_GROUP)
nsecs = 1000 * mi->overhead / MINSTREL_TRUNC(mi->avg_ampdu_len);
nsecs += minstrel_mcs_groups[group].duration[rate];
/* prob is scaled - see MINSTREL_FRAC above */
tp = 1000000 * ((prob * 1000) / nsecs);
mr->cur_tp = MINSTREL_TRUNC(tp);
}
/*
* Find & sort topmost throughput rates
*
* If multiple rates provide equal throughput the sorting is based on their
* current success probability. Higher success probability is preferred among
* MCS groups, CCK rates do not provide aggregation and are therefore at last.
*/
static void
minstrel_ht_sort_best_tp_rates(struct minstrel_ht_sta *mi, u16 index,
u16 *tp_list)
{
int cur_group, cur_idx, cur_thr, cur_prob;
int tmp_group, tmp_idx, tmp_thr, tmp_prob;
int j = MAX_THR_RATES;
cur_group = index / MCS_GROUP_RATES;
cur_idx = index % MCS_GROUP_RATES;
cur_thr = mi->groups[cur_group].rates[cur_idx].cur_tp;
cur_prob = mi->groups[cur_group].rates[cur_idx].probability;
do {
tmp_group = tp_list[j - 1] / MCS_GROUP_RATES;
tmp_idx = tp_list[j - 1] % MCS_GROUP_RATES;
tmp_thr = mi->groups[tmp_group].rates[tmp_idx].cur_tp;
tmp_prob = mi->groups[tmp_group].rates[tmp_idx].probability;
if (cur_thr < tmp_thr ||
(cur_thr == tmp_thr && cur_prob <= tmp_prob))
break;
j--;
} while (j > 0);
if (j < MAX_THR_RATES - 1) {
memmove(&tp_list[j + 1], &tp_list[j], (sizeof(*tp_list) *
(MAX_THR_RATES - (j + 1))));
}
if (j < MAX_THR_RATES)
tp_list[j] = index;
}
/*
* Find and set the topmost probability rate per sta and per group
*/
static void
minstrel_ht_set_best_prob_rate(struct minstrel_ht_sta *mi, u16 index)
{
struct minstrel_mcs_group_data *mg;
struct minstrel_rate_stats *mr;
int tmp_group, tmp_idx, tmp_tp, tmp_prob, max_tp_group;
mg = &mi->groups[index / MCS_GROUP_RATES];
mr = &mg->rates[index % MCS_GROUP_RATES];
tmp_group = mi->max_prob_rate / MCS_GROUP_RATES;
tmp_idx = mi->max_prob_rate % MCS_GROUP_RATES;
tmp_tp = mi->groups[tmp_group].rates[tmp_idx].cur_tp;
tmp_prob = mi->groups[tmp_group].rates[tmp_idx].probability;
/* if max_tp_rate[0] is from MCS_GROUP max_prob_rate get selected from
* MCS_GROUP as well as CCK_GROUP rates do not allow aggregation */
max_tp_group = mi->max_tp_rate[0] / MCS_GROUP_RATES;
if((index / MCS_GROUP_RATES == MINSTREL_CCK_GROUP) &&
(max_tp_group != MINSTREL_CCK_GROUP))
return;
if (mr->probability > MINSTREL_FRAC(75, 100)) {
if (mr->cur_tp > tmp_tp)
mi->max_prob_rate = index;
if (mr->cur_tp > mg->rates[mg->max_group_prob_rate].cur_tp)
mg->max_group_prob_rate = index;
} else {
if (mr->probability > tmp_prob)
mi->max_prob_rate = index;
if (mr->probability > mg->rates[mg->max_group_prob_rate].probability)
mg->max_group_prob_rate = index;
}
}
/*
* Assign new rate set per sta and use CCK rates only if the fastest
* rate (max_tp_rate[0]) is from CCK group. This prohibits such sorted
* rate sets where MCS and CCK rates are mixed, because CCK rates can
* not use aggregation.
*/
static void
minstrel_ht_assign_best_tp_rates(struct minstrel_ht_sta *mi,
u16 tmp_mcs_tp_rate[MAX_THR_RATES],
u16 tmp_cck_tp_rate[MAX_THR_RATES])
{
unsigned int tmp_group, tmp_idx, tmp_cck_tp, tmp_mcs_tp;
int i;
tmp_group = tmp_cck_tp_rate[0] / MCS_GROUP_RATES;
tmp_idx = tmp_cck_tp_rate[0] % MCS_GROUP_RATES;
tmp_cck_tp = mi->groups[tmp_group].rates[tmp_idx].cur_tp;
tmp_group = tmp_mcs_tp_rate[0] / MCS_GROUP_RATES;
tmp_idx = tmp_mcs_tp_rate[0] % MCS_GROUP_RATES;
tmp_mcs_tp = mi->groups[tmp_group].rates[tmp_idx].cur_tp;
if (tmp_cck_tp > tmp_mcs_tp) {
for(i = 0; i < MAX_THR_RATES; i++) {
minstrel_ht_sort_best_tp_rates(mi, tmp_cck_tp_rate[i],
tmp_mcs_tp_rate);
}
}
}
/*
* Try to increase robustness of max_prob rate by decrease number of
* streams if possible.
*/
static inline void
minstrel_ht_prob_rate_reduce_streams(struct minstrel_ht_sta *mi)
{
struct minstrel_mcs_group_data *mg;
struct minstrel_rate_stats *mr;
int tmp_max_streams, group;
int tmp_tp = 0;
tmp_max_streams = minstrel_mcs_groups[mi->max_tp_rate[0] /
MCS_GROUP_RATES].streams;
for (group = 0; group < ARRAY_SIZE(minstrel_mcs_groups); group++) {
mg = &mi->groups[group];
if (!mg->supported || group == MINSTREL_CCK_GROUP)
continue;
mr = minstrel_get_ratestats(mi, mg->max_group_prob_rate);
if (tmp_tp < mr->cur_tp &&
(minstrel_mcs_groups[group].streams < tmp_max_streams)) {
mi->max_prob_rate = mg->max_group_prob_rate;
tmp_tp = mr->cur_tp;
}
}
}
/*
* Update rate statistics and select new primary rates
*
* Rules for rate selection:
* - max_prob_rate must use only one stream, as a tradeoff between delivery
* probability and throughput during strong fluctuations
* - as long as the max prob rate has a probability of more than 75%, pick
* higher throughput rates, even if the probablity is a bit lower
*/
static void
minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
{
struct minstrel_mcs_group_data *mg;
struct minstrel_rate_stats *mr;
int group, i, j;
u16 tmp_mcs_tp_rate[MAX_THR_RATES], tmp_group_tp_rate[MAX_THR_RATES];
u16 tmp_cck_tp_rate[MAX_THR_RATES], index;
if (mi->ampdu_packets > 0) {
mi->avg_ampdu_len = minstrel_ewma(mi->avg_ampdu_len,
MINSTREL_FRAC(mi->ampdu_len, mi->ampdu_packets), EWMA_LEVEL);
mi->ampdu_len = 0;
mi->ampdu_packets = 0;
}
mi->sample_slow = 0;
mi->sample_count = 0;
/* Initialize global rate indexes */
for(j = 0; j < MAX_THR_RATES; j++){
tmp_mcs_tp_rate[j] = 0;
tmp_cck_tp_rate[j] = 0;
}
/* Find best rate sets within all MCS groups*/
for (group = 0; group < ARRAY_SIZE(minstrel_mcs_groups); group++) {
mg = &mi->groups[group];
if (!mg->supported)
continue;
mi->sample_count++;
/* (re)Initialize group rate indexes */
for(j = 0; j < MAX_THR_RATES; j++)
tmp_group_tp_rate[j] = group;
for (i = 0; i < MCS_GROUP_RATES; i++) {
if (!(mg->supported & BIT(i)))
continue;
index = MCS_GROUP_RATES * group + i;
mr = &mg->rates[i];
mr->retry_updated = false;
minstrel_calc_rate_ewma(mr);
minstrel_ht_calc_tp(mi, group, i);
if (!mr->cur_tp)
continue;
/* Find max throughput rate set */
if (group != MINSTREL_CCK_GROUP) {
minstrel_ht_sort_best_tp_rates(mi, index,
tmp_mcs_tp_rate);
} else if (group == MINSTREL_CCK_GROUP) {
minstrel_ht_sort_best_tp_rates(mi, index,
tmp_cck_tp_rate);
}
/* Find max throughput rate set within a group */
minstrel_ht_sort_best_tp_rates(mi, index,
tmp_group_tp_rate);
/* Find max probability rate per group and global */
minstrel_ht_set_best_prob_rate(mi, index);
}
memcpy(mg->max_group_tp_rate, tmp_group_tp_rate,
sizeof(mg->max_group_tp_rate));
}
/* Assign new rate set per sta */
minstrel_ht_assign_best_tp_rates(mi, tmp_mcs_tp_rate, tmp_cck_tp_rate);
memcpy(mi->max_tp_rate, tmp_mcs_tp_rate, sizeof(mi->max_tp_rate));
/* Try to increase robustness of max_prob_rate*/
minstrel_ht_prob_rate_reduce_streams(mi);
/* try to sample all available rates during each interval */
mi->sample_count *= 8;
#ifdef CONFIG_MAC80211_DEBUGFS
/* use fixed index if set */
if (mp->fixed_rate_idx != -1) {
for (i = 0; i < 4; i++)
mi->max_tp_rate[i] = mp->fixed_rate_idx;
mi->max_prob_rate = mp->fixed_rate_idx;
}
#endif
/* Reset update timer */
mi->stats_update = jiffies;
}
static bool
minstrel_ht_txstat_valid(struct minstrel_priv *mp, struct ieee80211_tx_rate *rate)
{
if (rate->idx < 0)
return false;
if (!rate->count)
return false;
if (rate->flags & IEEE80211_TX_RC_MCS ||
rate->flags & IEEE80211_TX_RC_VHT_MCS)
return true;
return rate->idx == mp->cck_rates[0] ||
rate->idx == mp->cck_rates[1] ||
rate->idx == mp->cck_rates[2] ||
rate->idx == mp->cck_rates[3];
}
static void
minstrel_next_sample_idx(struct minstrel_ht_sta *mi)
{
struct minstrel_mcs_group_data *mg;
for (;;) {
mi->sample_group++;
mi->sample_group %= ARRAY_SIZE(minstrel_mcs_groups);
mg = &mi->groups[mi->sample_group];
if (!mg->supported)
continue;
if (++mg->index >= MCS_GROUP_RATES) {
mg->index = 0;
if (++mg->column >= ARRAY_SIZE(sample_table))
mg->column = 0;
}
break;
}
}
static void
minstrel_downgrade_rate(struct minstrel_ht_sta *mi, u16 *idx, bool primary)
{
int group, orig_group;
orig_group = group = *idx / MCS_GROUP_RATES;
while (group > 0) {
group--;
if (!mi->groups[group].supported)
continue;
if (minstrel_mcs_groups[group].streams >
minstrel_mcs_groups[orig_group].streams)
continue;
if (primary)
*idx = mi->groups[group].max_group_tp_rate[0];
else
*idx = mi->groups[group].max_group_tp_rate[1];
break;
}
}
static void
minstrel_aggr_check(struct ieee80211_sta *pubsta, struct sk_buff *skb)
{
struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
struct sta_info *sta = container_of(pubsta, struct sta_info, sta);
u16 tid;
if (skb_get_queue_mapping(skb) == IEEE80211_AC_VO)
return;
if (unlikely(!ieee80211_is_data_qos(hdr->frame_control)))
return;
if (unlikely(skb->protocol == cpu_to_be16(ETH_P_PAE)))
return;
tid = *ieee80211_get_qos_ctl(hdr) & IEEE80211_QOS_CTL_TID_MASK;
if (likely(sta->ampdu_mlme.tid_tx[tid]))
return;
ieee80211_start_tx_ba_session(pubsta, tid, 5000);
}
static void
minstrel_ht_tx_status(void *priv, struct ieee80211_supported_band *sband,
struct ieee80211_sta *sta, void *priv_sta,
struct ieee80211_tx_info *info)
{
struct minstrel_ht_sta_priv *msp = priv_sta;
struct minstrel_ht_sta *mi = &msp->ht;
struct ieee80211_tx_rate *ar = info->status.rates;
struct minstrel_rate_stats *rate, *rate2;
struct minstrel_priv *mp = priv;
bool last, update = false;
int i;
if (!msp->is_ht)
return mac80211_minstrel.tx_status_noskb(priv, sband, sta,
&msp->legacy, info);
/* This packet was aggregated but doesn't carry status info */
if ((info->flags & IEEE80211_TX_CTL_AMPDU) &&
!(info->flags & IEEE80211_TX_STAT_AMPDU))
return;
if (!(info->flags & IEEE80211_TX_STAT_AMPDU)) {
info->status.ampdu_ack_len =
(info->flags & IEEE80211_TX_STAT_ACK ? 1 : 0);
info->status.ampdu_len = 1;
}
mi->ampdu_packets++;
mi->ampdu_len += info->status.ampdu_len;
if (!mi->sample_wait && !mi->sample_tries && mi->sample_count > 0) {
mi->sample_wait = 16 + 2 * MINSTREL_TRUNC(mi->avg_ampdu_len);
mi->sample_tries = 1;
mi->sample_count--;
}
if (info->flags & IEEE80211_TX_CTL_RATE_CTRL_PROBE)
mi->sample_packets += info->status.ampdu_len;
last = !minstrel_ht_txstat_valid(mp, &ar[0]);
for (i = 0; !last; i++) {
last = (i == IEEE80211_TX_MAX_RATES - 1) ||
!minstrel_ht_txstat_valid(mp, &ar[i + 1]);
rate = minstrel_ht_get_stats(mp, mi, &ar[i]);
if (last)
rate->success += info->status.ampdu_ack_len;
rate->attempts += ar[i].count * info->status.ampdu_len;
}
/*
* check for sudden death of spatial multiplexing,
* downgrade to a lower number of streams if necessary.
*/
rate = minstrel_get_ratestats(mi, mi->max_tp_rate[0]);
if (rate->attempts > 30 &&
MINSTREL_FRAC(rate->success, rate->attempts) <
MINSTREL_FRAC(20, 100)) {
minstrel_downgrade_rate(mi, &mi->max_tp_rate[0], true);
update = true;
}
rate2 = minstrel_get_ratestats(mi, mi->max_tp_rate[1]);
if (rate2->attempts > 30 &&
MINSTREL_FRAC(rate2->success, rate2->attempts) <
MINSTREL_FRAC(20, 100)) {
minstrel_downgrade_rate(mi, &mi->max_tp_rate[1], false);
update = true;
}
if (time_after(jiffies, mi->stats_update + (mp->update_interval / 2 * HZ) / 1000)) {
update = true;
minstrel_ht_update_stats(mp, mi);
}
if (update)
minstrel_ht_update_rates(mp, mi);
}
static void
minstrel_calc_retransmit(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
int index)
{
struct minstrel_rate_stats *mr;
const struct mcs_group *group;
unsigned int tx_time, tx_time_rtscts, tx_time_data;
unsigned int cw = mp->cw_min;
unsigned int ctime = 0;
unsigned int t_slot = 9; /* FIXME */
unsigned int ampdu_len = MINSTREL_TRUNC(mi->avg_ampdu_len);
unsigned int overhead = 0, overhead_rtscts = 0;
mr = minstrel_get_ratestats(mi, index);
if (mr->probability < MINSTREL_FRAC(1, 10)) {
mr->retry_count = 1;
mr->retry_count_rtscts = 1;
return;
}
mr->retry_count = 2;
mr->retry_count_rtscts = 2;
mr->retry_updated = true;
group = &minstrel_mcs_groups[index / MCS_GROUP_RATES];
tx_time_data = group->duration[index % MCS_GROUP_RATES] * ampdu_len / 1000;
/* Contention time for first 2 tries */
ctime = (t_slot * cw) >> 1;
cw = min((cw << 1) | 1, mp->cw_max);
ctime += (t_slot * cw) >> 1;
cw = min((cw << 1) | 1, mp->cw_max);
if (index / MCS_GROUP_RATES != MINSTREL_CCK_GROUP) {
overhead = mi->overhead;
overhead_rtscts = mi->overhead_rtscts;
}
/* Total TX time for data and Contention after first 2 tries */
tx_time = ctime + 2 * (overhead + tx_time_data);
tx_time_rtscts = ctime + 2 * (overhead_rtscts + tx_time_data);
/* See how many more tries we can fit inside segment size */
do {
/* Contention time for this try */
ctime = (t_slot * cw) >> 1;
cw = min((cw << 1) | 1, mp->cw_max);
/* Total TX time after this try */
tx_time += ctime + overhead + tx_time_data;
tx_time_rtscts += ctime + overhead_rtscts + tx_time_data;
if (tx_time_rtscts < mp->segment_size)
mr->retry_count_rtscts++;
} while ((tx_time < mp->segment_size) &&
(++mr->retry_count < mp->max_retry));
}
static void
minstrel_ht_set_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
struct ieee80211_sta_rates *ratetbl, int offset, int index)
{
const struct mcs_group *group = &minstrel_mcs_groups[index / MCS_GROUP_RATES];
struct minstrel_rate_stats *mr;
u8 idx;
u16 flags = group->flags;
mr = minstrel_get_ratestats(mi, index);
if (!mr->retry_updated)
minstrel_calc_retransmit(mp, mi, index);
if (mr->probability < MINSTREL_FRAC(20, 100) || !mr->retry_count) {
ratetbl->rate[offset].count = 2;
ratetbl->rate[offset].count_rts = 2;
ratetbl->rate[offset].count_cts = 2;
} else {
ratetbl->rate[offset].count = mr->retry_count;
ratetbl->rate[offset].count_cts = mr->retry_count;
ratetbl->rate[offset].count_rts = mr->retry_count_rtscts;
}
if (index / MCS_GROUP_RATES == MINSTREL_CCK_GROUP)
idx = mp->cck_rates[index % ARRAY_SIZE(mp->cck_rates)];
else if (flags & IEEE80211_TX_RC_VHT_MCS)
idx = ((group->streams - 1) << 4) |
((index % MCS_GROUP_RATES) & 0xF);
else
idx = index % MCS_GROUP_RATES + (group->streams - 1) * 8;
if (offset > 0) {
ratetbl->rate[offset].count = ratetbl->rate[offset].count_rts;
flags |= IEEE80211_TX_RC_USE_RTS_CTS;
}
ratetbl->rate[offset].idx = idx;
ratetbl->rate[offset].flags = flags;
}
static void
minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
{
struct ieee80211_sta_rates *rates;
int i = 0;
rates = kzalloc(sizeof(*rates), GFP_ATOMIC);
if (!rates)
return;
/* Start with max_tp_rate[0] */
minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_tp_rate[0]);
if (mp->hw->max_rates >= 3) {
/* At least 3 tx rates supported, use max_tp_rate[1] next */
minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_tp_rate[1]);
}
if (mp->hw->max_rates >= 2) {
/*
* At least 2 tx rates supported, use max_prob_rate next */
minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_prob_rate);
}
rates->rate[i].idx = -1;
rate_control_set_rates(mp->hw, mi->sta, rates);
}
static inline int
minstrel_get_duration(int index)
{
const struct mcs_group *group = &minstrel_mcs_groups[index / MCS_GROUP_RATES];
return group->duration[index % MCS_GROUP_RATES];
}
static int
minstrel_get_sample_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
{
struct minstrel_rate_stats *mr;
struct minstrel_mcs_group_data *mg;
unsigned int sample_dur, sample_group, cur_max_tp_streams;
int sample_idx = 0;
if (mi->sample_wait > 0) {
mi->sample_wait--;
return -1;
}
if (!mi->sample_tries)
return -1;
sample_group = mi->sample_group;
mg = &mi->groups[sample_group];
sample_idx = sample_table[mg->column][mg->index];
minstrel_next_sample_idx(mi);
if (!(mg->supported & BIT(sample_idx)))
return -1;
mr = &mg->rates[sample_idx];
sample_idx += sample_group * MCS_GROUP_RATES;
/*
* Sampling might add some overhead (RTS, no aggregation)
* to the frame. Hence, don't use sampling for the currently
* used rates.
*/
if (sample_idx == mi->max_tp_rate[0] ||
sample_idx == mi->max_tp_rate[1] ||
sample_idx == mi->max_prob_rate)
return -1;
/*
* Do not sample if the probability is already higher than 95%
* to avoid wasting airtime.
*/
if (mr->probability > MINSTREL_FRAC(95, 100))
return -1;
/*
* Make sure that lower rates get sampled only occasionally,
* if the link is working perfectly.
*/
cur_max_tp_streams = minstrel_mcs_groups[mi->max_tp_rate[0] /
MCS_GROUP_RATES].streams;
sample_dur = minstrel_get_duration(sample_idx);
if (sample_dur >= minstrel_get_duration(mi->max_tp_rate[1]) &&
(cur_max_tp_streams - 1 <
minstrel_mcs_groups[sample_group].streams ||
sample_dur >= minstrel_get_duration(mi->max_prob_rate))) {
if (mr->sample_skipped < 20)
return -1;
if (mi->sample_slow++ > 2)
return -1;
}
mi->sample_tries--;
return sample_idx;
}
static void
minstrel_ht_check_cck_shortpreamble(struct minstrel_priv *mp,
struct minstrel_ht_sta *mi, bool val)
{
u8 supported = mi->groups[MINSTREL_CCK_GROUP].supported;
if (!supported || !mi->cck_supported_short)
return;
if (supported & (mi->cck_supported_short << (val * 4)))
return;
supported ^= mi->cck_supported_short | (mi->cck_supported_short << 4);
mi->groups[MINSTREL_CCK_GROUP].supported = supported;
}
static void
minstrel_ht_get_rate(void *priv, struct ieee80211_sta *sta, void *priv_sta,
struct ieee80211_tx_rate_control *txrc)
{
const struct mcs_group *sample_group;
struct ieee80211_tx_info *info = IEEE80211_SKB_CB(txrc->skb);
struct ieee80211_tx_rate *rate = &info->status.rates[0];
struct minstrel_ht_sta_priv *msp = priv_sta;
struct minstrel_ht_sta *mi = &msp->ht;
struct minstrel_priv *mp = priv;
int sample_idx;
if (rate_control_send_low(sta, priv_sta, txrc))
return;
if (!msp->is_ht)
return mac80211_minstrel.get_rate(priv, sta, &msp->legacy, txrc);
if (!(info->flags & IEEE80211_TX_CTL_AMPDU) &&
mi->max_prob_rate / MCS_GROUP_RATES != MINSTREL_CCK_GROUP)
minstrel_aggr_check(sta, txrc->skb);
info->flags |= mi->tx_flags;
minstrel_ht_check_cck_shortpreamble(mp, mi, txrc->short_preamble);
#ifdef CONFIG_MAC80211_DEBUGFS
if (mp->fixed_rate_idx != -1)
return;
#endif
/* Don't use EAPOL frames for sampling on non-mrr hw */
if (mp->hw->max_rates == 1 &&
(info->control.flags & IEEE80211_TX_CTRL_PORT_CTRL_PROTO))
sample_idx = -1;
else
sample_idx = minstrel_get_sample_rate(mp, mi);
mi->total_packets++;
/* wraparound */
if (mi->total_packets == ~0) {
mi->total_packets = 0;
mi->sample_packets = 0;
}
if (sample_idx < 0)
return;
sample_group = &minstrel_mcs_groups[sample_idx / MCS_GROUP_RATES];
info->flags |= IEEE80211_TX_CTL_RATE_CTRL_PROBE;
rate->count = 1;
if (sample_idx / MCS_GROUP_RATES == MINSTREL_CCK_GROUP) {
int idx = sample_idx % ARRAY_SIZE(mp->cck_rates);
rate->idx = mp->cck_rates[idx];
} else if (sample_group->flags & IEEE80211_TX_RC_VHT_MCS) {
ieee80211_rate_set_vht(rate, sample_idx % MCS_GROUP_RATES,
sample_group->streams);
} else {
rate->idx = sample_idx % MCS_GROUP_RATES +
(sample_group->streams - 1) * 8;
}
rate->flags = sample_group->flags;
}
static void
minstrel_ht_update_cck(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
struct ieee80211_supported_band *sband,
struct ieee80211_sta *sta)
{
int i;
if (sband->band != IEEE80211_BAND_2GHZ)
return;
if (!(mp->hw->flags & IEEE80211_HW_SUPPORTS_HT_CCK_RATES))
return;
mi->cck_supported = 0;
mi->cck_supported_short = 0;
for (i = 0; i < 4; i++) {
if (!rate_supported(sta, sband->band, mp->cck_rates[i]))
continue;
mi->cck_supported |= BIT(i);
if (sband->bitrates[i].flags & IEEE80211_RATE_SHORT_PREAMBLE)
mi->cck_supported_short |= BIT(i);
}
mi->groups[MINSTREL_CCK_GROUP].supported = mi->cck_supported;
}
static void
minstrel_ht_update_caps(void *priv, struct ieee80211_supported_band *sband,
struct cfg80211_chan_def *chandef,
struct ieee80211_sta *sta, void *priv_sta)
{
struct minstrel_priv *mp = priv;
struct minstrel_ht_sta_priv *msp = priv_sta;
struct minstrel_ht_sta *mi = &msp->ht;
struct ieee80211_mcs_info *mcs = &sta->ht_cap.mcs;
u16 sta_cap = sta->ht_cap.cap;
struct ieee80211_sta_vht_cap *vht_cap = &sta->vht_cap;
int use_vht;
int n_supported = 0;
int ack_dur;
int stbc;
int i;
/* fall back to the old minstrel for legacy stations */
if (!sta->ht_cap.ht_supported)
goto use_legacy;
BUILD_BUG_ON(ARRAY_SIZE(minstrel_mcs_groups) != MINSTREL_GROUPS_NB);
#ifdef CONFIG_MAC80211_RC_MINSTREL_VHT
if (vht_cap->vht_supported)
use_vht = vht_cap->vht_mcs.tx_mcs_map != cpu_to_le16(~0);
else
#endif
use_vht = 0;
msp->is_ht = true;
memset(mi, 0, sizeof(*mi));
mi->sta = sta;
mi->stats_update = jiffies;
ack_dur = ieee80211_frame_duration(sband->band, 10, 60, 1, 1, 0);
mi->overhead = ieee80211_frame_duration(sband->band, 0, 60, 1, 1, 0);
mi->overhead += ack_dur;
mi->overhead_rtscts = mi->overhead + 2 * ack_dur;
mi->avg_ampdu_len = MINSTREL_FRAC(1, 1);
/* When using MRR, sample more on the first attempt, without delay */
if (mp->has_mrr) {
mi->sample_count = 16;
mi->sample_wait = 0;
} else {
mi->sample_count = 8;
mi->sample_wait = 8;
}
mi->sample_tries = 4;
/* TODO tx_flags for vht - ATM the RC API is not fine-grained enough */
if (!use_vht) {
stbc = (sta_cap & IEEE80211_HT_CAP_RX_STBC) >>
IEEE80211_HT_CAP_RX_STBC_SHIFT;
mi->tx_flags |= stbc << IEEE80211_TX_CTL_STBC_SHIFT;
if (sta_cap & IEEE80211_HT_CAP_LDPC_CODING)
mi->tx_flags |= IEEE80211_TX_CTL_LDPC;
}
for (i = 0; i < ARRAY_SIZE(mi->groups); i++) {
u32 gflags = minstrel_mcs_groups[i].flags;
int bw, nss;
mi->groups[i].supported = 0;
if (i == MINSTREL_CCK_GROUP) {
minstrel_ht_update_cck(mp, mi, sband, sta);
continue;
}
if (gflags & IEEE80211_TX_RC_SHORT_GI) {
if (gflags & IEEE80211_TX_RC_40_MHZ_WIDTH) {
if (!(sta_cap & IEEE80211_HT_CAP_SGI_40))
continue;
} else {
if (!(sta_cap & IEEE80211_HT_CAP_SGI_20))
continue;
}
}
if (gflags & IEEE80211_TX_RC_40_MHZ_WIDTH &&
sta->bandwidth < IEEE80211_STA_RX_BW_40)
continue;
nss = minstrel_mcs_groups[i].streams;
/* Mark MCS > 7 as unsupported if STA is in static SMPS mode */
if (sta->smps_mode == IEEE80211_SMPS_STATIC && nss > 1)
continue;
/* HT rate */
if (gflags & IEEE80211_TX_RC_MCS) {
#ifdef CONFIG_MAC80211_RC_MINSTREL_VHT
if (use_vht && minstrel_vht_only)
continue;
#endif
mi->groups[i].supported = mcs->rx_mask[nss - 1];
if (mi->groups[i].supported)
n_supported++;
continue;
}
/* VHT rate */
if (!vht_cap->vht_supported ||
WARN_ON(!(gflags & IEEE80211_TX_RC_VHT_MCS)) ||
WARN_ON(gflags & IEEE80211_TX_RC_160_MHZ_WIDTH))
continue;
if (gflags & IEEE80211_TX_RC_80_MHZ_WIDTH) {
if (sta->bandwidth < IEEE80211_STA_RX_BW_80 ||
((gflags & IEEE80211_TX_RC_SHORT_GI) &&
!(vht_cap->cap & IEEE80211_VHT_CAP_SHORT_GI_80))) {
continue;
}
}
if (gflags & IEEE80211_TX_RC_40_MHZ_WIDTH)
bw = BW_40;
else if (gflags & IEEE80211_TX_RC_80_MHZ_WIDTH)
bw = BW_80;
else
bw = BW_20;
mi->groups[i].supported = minstrel_get_valid_vht_rates(bw, nss,
vht_cap->vht_mcs.tx_mcs_map);
if (mi->groups[i].supported)
n_supported++;
}
if (!n_supported)
goto use_legacy;
/* create an initial rate table with the lowest supported rates */
minstrel_ht_update_stats(mp, mi);
minstrel_ht_update_rates(mp, mi);
return;
use_legacy:
msp->is_ht = false;
memset(&msp->legacy, 0, sizeof(msp->legacy));
msp->legacy.r = msp->ratelist;
msp->legacy.sample_table = msp->sample_table;
return mac80211_minstrel.rate_init(priv, sband, chandef, sta,
&msp->legacy);
}
static void
minstrel_ht_rate_init(void *priv, struct ieee80211_supported_band *sband,
struct cfg80211_chan_def *chandef,
struct ieee80211_sta *sta, void *priv_sta)
{
minstrel_ht_update_caps(priv, sband, chandef, sta, priv_sta);
}
static void
minstrel_ht_rate_update(void *priv, struct ieee80211_supported_band *sband,
struct cfg80211_chan_def *chandef,
struct ieee80211_sta *sta, void *priv_sta,
u32 changed)
{
minstrel_ht_update_caps(priv, sband, chandef, sta, priv_sta);
}
static void *
minstrel_ht_alloc_sta(void *priv, struct ieee80211_sta *sta, gfp_t gfp)
{
struct ieee80211_supported_band *sband;
struct minstrel_ht_sta_priv *msp;
struct minstrel_priv *mp = priv;
struct ieee80211_hw *hw = mp->hw;
int max_rates = 0;
int i;
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;
}
msp = kzalloc(sizeof(*msp), gfp);
if (!msp)
return NULL;
msp->ratelist = kzalloc(sizeof(struct minstrel_rate) * max_rates, gfp);
if (!msp->ratelist)
goto error;
msp->sample_table = kmalloc(SAMPLE_COLUMNS * max_rates, gfp);
if (!msp->sample_table)
goto error1;
return msp;
error1:
kfree(msp->ratelist);
error:
kfree(msp);
return NULL;
}
static void
minstrel_ht_free_sta(void *priv, struct ieee80211_sta *sta, void *priv_sta)
{
struct minstrel_ht_sta_priv *msp = priv_sta;
kfree(msp->sample_table);
kfree(msp->ratelist);
kfree(msp);
}
static void *
minstrel_ht_alloc(struct ieee80211_hw *hw, struct dentry *debugfsdir)
{
return mac80211_minstrel.alloc(hw, debugfsdir);
}
static void
minstrel_ht_free(void *priv)
{
mac80211_minstrel.free(priv);
}
static u32 minstrel_ht_get_expected_throughput(void *priv_sta)
{
struct minstrel_ht_sta_priv *msp = priv_sta;
struct minstrel_ht_sta *mi = &msp->ht;
int i, j;
if (!msp->is_ht)
return mac80211_minstrel.get_expected_throughput(priv_sta);
i = mi->max_tp_rate[0] / MCS_GROUP_RATES;
j = mi->max_tp_rate[0] % MCS_GROUP_RATES;
/* convert cur_tp from pkt per second in kbps */
return mi->groups[i].rates[j].cur_tp * AVG_PKT_SIZE * 8 / 1024;
}
static const struct rate_control_ops mac80211_minstrel_ht = {
.name = "minstrel_ht",
.tx_status_noskb = minstrel_ht_tx_status,
.get_rate = minstrel_ht_get_rate,
.rate_init = minstrel_ht_rate_init,
.rate_update = minstrel_ht_rate_update,
.alloc_sta = minstrel_ht_alloc_sta,
.free_sta = minstrel_ht_free_sta,
.alloc = minstrel_ht_alloc,
.free = minstrel_ht_free,
#ifdef CONFIG_MAC80211_DEBUGFS
.add_sta_debugfs = minstrel_ht_add_sta_debugfs,
.remove_sta_debugfs = minstrel_ht_remove_sta_debugfs,
#endif
.get_expected_throughput = minstrel_ht_get_expected_throughput,
};
static void __init init_sample_table(void)
{
int col, i, new_idx;
u8 rnd[MCS_GROUP_RATES];
memset(sample_table, 0xff, sizeof(sample_table));
for (col = 0; col < SAMPLE_COLUMNS; col++) {
prandom_bytes(rnd, sizeof(rnd));
for (i = 0; i < MCS_GROUP_RATES; i++) {
new_idx = (i + rnd[i]) % MCS_GROUP_RATES;
while (sample_table[col][new_idx] != 0xff)
new_idx = (new_idx + 1) % MCS_GROUP_RATES;
sample_table[col][new_idx] = i;
}
}
}
int __init
rc80211_minstrel_ht_init(void)
{
init_sample_table();
return ieee80211_rate_control_register(&mac80211_minstrel_ht);
}
void
rc80211_minstrel_ht_exit(void)
{
ieee80211_rate_control_unregister(&mac80211_minstrel_ht);
}
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