--- /dev/null
+From: Felix Fietkau <nbd@nbd.name>
+Date: Fri, 14 Jun 2019 21:15:47 +0200
+Subject: [PATCH] mac80211: minstrel_ht: improve rate probing for devices
+ with static fallback
+
+On some devices that only support static rate fallback tables sending rate
+control probing packets can be really expensive.
+Probing lower rates can already hurt throughput quite a bit. What hurts even
+more is the fact that on mt76x0/mt76x2, single probing packets can only be
+forced by directing packets at a different internal hardware queue, which
+causes some heavy reordering and extra latency.
+The reordering issue is mainly problematic while pushing lots of packets to
+a particular station. If there is little activity, the overhead of probing is
+neglegible.
+
+The static fallback behavior is designed to pretty much only handle rate
+control algorithms that use only a very limited set of rates on which the
+algorithm switches up/down based on packet error rate.
+
+In order to better support that kind of hardware, this patch implements a
+different approach to rate probing where it switches to a slightly higher rate,
+waits for tx status feedback, then updates the stats and switches back to
+the new max throughput rate. This only triggers above a packet rate of 100
+per stats interval (~50ms).
+For that kind of probing, the code has to reduce the set of probing rates
+a lot more compared to single packet probing, so it uses only one packet
+per MCS group which is either slightly faster, or as close as possible to
+the max throughput rate.
+This allows switching between similar rates with different numbers of
+streams. The algorithm assumes that the hardware will work its way lower
+within an MCS group in case of retransmissions, so that lower rates don't
+have to be probed by the high packets per second rate probing code.
+
+To further reduce the search space, it also does not probe rates with lower
+channel bandwidth than the max throughput rate.
+
+At the moment, these changes will only affect mt76x0/mt76x2.
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/rc80211_minstrel.h
++++ b/net/mac80211/rc80211_minstrel.h
+@@ -95,6 +95,7 @@ struct minstrel_sta_info {
+ struct minstrel_priv {
+ struct ieee80211_hw *hw;
+ bool has_mrr;
++ u32 sample_switch;
+ unsigned int cw_min;
+ unsigned int cw_max;
+ unsigned int max_retry;
+--- a/net/mac80211/rc80211_minstrel_ht.c
++++ b/net/mac80211/rc80211_minstrel_ht.c
+@@ -18,6 +18,8 @@
+ #define AVG_AMPDU_SIZE 16
+ #define AVG_PKT_SIZE 1200
+
++#define SAMPLE_SWITCH_THR 100
++
+ /* Number of bits for an average sized packet */
+ #define MCS_NBITS ((AVG_PKT_SIZE * AVG_AMPDU_SIZE) << 3)
+
+@@ -58,6 +60,7 @@
+ [GROUP_IDX(_streams, _sgi, _ht40)] = { \
+ .streams = _streams, \
+ .shift = _s, \
++ .bw = _ht40, \
+ .flags = \
+ IEEE80211_TX_RC_MCS | \
+ (_sgi ? IEEE80211_TX_RC_SHORT_GI : 0) | \
+@@ -94,6 +97,7 @@
+ [VHT_GROUP_IDX(_streams, _sgi, _bw)] = { \
+ .streams = _streams, \
+ .shift = _s, \
++ .bw = _bw, \
+ .flags = \
+ IEEE80211_TX_RC_VHT_MCS | \
+ (_sgi ? IEEE80211_TX_RC_SHORT_GI : 0) | \
+@@ -526,6 +530,133 @@ minstrel_ht_prob_rate_reduce_streams(str
+ }
+ }
+
++static inline int
++minstrel_get_duration(int index)
++{
++ const struct mcs_group *group = &minstrel_mcs_groups[index / MCS_GROUP_RATES];
++ unsigned int duration = group->duration[index % MCS_GROUP_RATES];
++ return duration << group->shift;
++}
++
++static bool
++minstrel_ht_probe_group(struct minstrel_ht_sta *mi, const struct mcs_group *tp_group,
++ int tp_idx, const struct mcs_group *group)
++{
++ if (group->bw < tp_group->bw)
++ return false;
++
++ if (group->streams == tp_group->streams)
++ return true;
++
++ if (tp_idx < 4 && group->streams == tp_group->streams - 1)
++ return true;
++
++ return group->streams == tp_group->streams + 1;
++}
++
++static void
++minstrel_ht_find_probe_rates(struct minstrel_ht_sta *mi, u16 *rates, int *n_rates,
++ bool faster_rate)
++{
++ const struct mcs_group *group, *tp_group;
++ int i, g, max_dur;
++ int tp_idx;
++
++ tp_group = &minstrel_mcs_groups[mi->max_tp_rate[0] / MCS_GROUP_RATES];
++ tp_idx = mi->max_tp_rate[0] % MCS_GROUP_RATES;
++
++ max_dur = minstrel_get_duration(mi->max_tp_rate[0]);
++ if (faster_rate)
++ max_dur -= max_dur / 16;
++
++ for (g = 0; g < MINSTREL_GROUPS_NB; g++) {
++ u16 supported = mi->supported[g];
++
++ if (!supported)
++ continue;
++
++ group = &minstrel_mcs_groups[g];
++ if (!minstrel_ht_probe_group(mi, tp_group, tp_idx, group))
++ continue;
++
++ for (i = 0; supported; supported >>= 1, i++) {
++ int idx;
++
++ if (!(supported & 1))
++ continue;
++
++ if ((group->duration[i] << group->shift) > max_dur)
++ continue;
++
++ idx = g * MCS_GROUP_RATES + i;
++ if (idx == mi->max_tp_rate[0])
++ continue;
++
++ rates[(*n_rates)++] = idx;
++ break;
++ }
++ }
++}
++
++static void
++minstrel_ht_rate_sample_switch(struct minstrel_priv *mp,
++ struct minstrel_ht_sta *mi)
++{
++ struct minstrel_rate_stats *mrs;
++ u16 rates[MINSTREL_GROUPS_NB];
++ int n_rates = 0;
++ int probe_rate = 0;
++ bool faster_rate;
++ int i;
++ u8 random;
++
++ /*
++ * Use rate switching instead of probing packets for devices with
++ * little control over retry fallback behavior
++ */
++ if (mp->hw->max_rates > 1)
++ return;
++
++ /*
++ * If the current EWMA prob is >75%, look for a rate that's 6.25%
++ * faster than the max tp rate.
++ * If that fails, look again for a rate that is at least as fast
++ */
++ mrs = minstrel_get_ratestats(mi, mi->max_tp_rate[0]);
++ faster_rate = mrs->prob_ewma > MINSTREL_FRAC(75, 100);
++ minstrel_ht_find_probe_rates(mi, rates, &n_rates, faster_rate);
++ if (!n_rates && faster_rate)
++ minstrel_ht_find_probe_rates(mi, rates, &n_rates, false);
++
++ /* If no suitable rate was found, try to pick the next one in the group */
++ if (!n_rates) {
++ int g_idx = mi->max_tp_rate[0] / MCS_GROUP_RATES;
++ u16 supported = mi->supported[g_idx];
++
++ supported >>= mi->max_tp_rate[0] % MCS_GROUP_RATES;
++ for (i = 0; supported; i++) {
++ if (!(supported & 1))
++ continue;
++
++ probe_rate = mi->max_tp_rate[0] + i;
++ goto out;
++ }
++
++ return;
++ }
++
++ i = 0;
++ if (n_rates > 1) {
++ random = prandom_u32();
++ i = random % n_rates;
++ }
++ probe_rate = rates[i];
++
++out:
++ mi->sample_rate = probe_rate;
++ mi->sample_mode = MINSTREL_SAMPLE_ACTIVE;
++}
++
+ /*
+ * Update rate statistics and select new primary rates
+ *
+@@ -536,7 +667,8 @@ minstrel_ht_prob_rate_reduce_streams(str
+ * 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)
++minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
++ bool sample)
+ {
+ struct minstrel_mcs_group_data *mg;
+ struct minstrel_rate_stats *mrs;
+@@ -544,6 +676,18 @@ minstrel_ht_update_stats(struct minstrel
+ u16 tmp_mcs_tp_rate[MAX_THR_RATES], tmp_group_tp_rate[MAX_THR_RATES];
+ u16 tmp_cck_tp_rate[MAX_THR_RATES], index;
+
++ mi->sample_mode = MINSTREL_SAMPLE_IDLE;
++
++ if (sample) {
++ mi->total_packets_cur = mi->total_packets -
++ mi->total_packets_last;
++ mi->total_packets_last = mi->total_packets;
++ }
++ if (!mp->sample_switch)
++ sample = false;
++ if (mi->total_packets_cur < SAMPLE_SWITCH_THR && mp->sample_switch != 1)
++ sample = false;
++
+ if (mi->ampdu_packets > 0) {
+ if (!ieee80211_hw_check(mp->hw, TX_STATUS_NO_AMPDU_LEN))
+ mi->avg_ampdu_len = minstrel_ewma(mi->avg_ampdu_len,
+@@ -630,12 +774,16 @@ minstrel_ht_update_stats(struct minstrel
+ /* try to sample all available rates during each interval */
+ mi->sample_count *= 8;
+
++ if (sample)
++ minstrel_ht_rate_sample_switch(mp, mi);
++
+ #ifdef CPTCFG_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;
++ mi->sample_mode = MINSTREL_SAMPLE_IDLE;
+ }
+ #endif
+
+@@ -739,15 +887,17 @@ minstrel_ht_tx_status(void *priv, struct
+ 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_rate_stats *rate, *rate2, *rate_sample = NULL;
+ struct minstrel_priv *mp = priv;
+ bool last, update = false;
++ bool sample_status = false;
+ int i;
+
+ if (!msp->is_ht)
+ return mac80211_minstrel.tx_status_ext(priv, sband,
+ &msp->legacy, st);
+
++
+ /* This packet was aggregated but doesn't carry status info */
+ if ((info->flags & IEEE80211_TX_CTL_AMPDU) &&
+ !(info->flags & IEEE80211_TX_STAT_AMPDU))
+@@ -773,12 +923,17 @@ minstrel_ht_tx_status(void *priv, struct
+ if (info->flags & IEEE80211_TX_CTL_RATE_CTRL_PROBE)
+ mi->sample_packets += info->status.ampdu_len;
+
++ if (mi->sample_mode != MINSTREL_SAMPLE_IDLE)
++ rate_sample = minstrel_get_ratestats(mi, mi->sample_rate);
++
+ 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 (rate == rate_sample)
++ sample_status = true;
+
+ if (last)
+ rate->success += info->status.ampdu_ack_len;
+@@ -786,44 +941,60 @@ minstrel_ht_tx_status(void *priv, struct
+ 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);
++ switch (mi->sample_mode) {
++ case MINSTREL_SAMPLE_IDLE:
++ break;
++
++ case MINSTREL_SAMPLE_ACTIVE:
++ if (!sample_status)
++ break;
++
++ mi->sample_mode = MINSTREL_SAMPLE_PENDING;
+ update = true;
+- }
++ break;
++
++ case MINSTREL_SAMPLE_PENDING:
++ if (sample_status)
++ break;
+
+- 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;
++ minstrel_ht_update_stats(mp, mi, false);
++ break;
++ }
++
++
++ if (mp->hw->max_rates > 1) {
++ /*
++ * 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->last_stats_update +
+ (mp->update_interval / 2 * HZ) / 1000)) {
+ update = true;
+- minstrel_ht_update_stats(mp, mi);
++ minstrel_ht_update_stats(mp, mi, true);
+ }
+
+ if (update)
+ minstrel_ht_update_rates(mp, mi);
+ }
+
+-static inline int
+-minstrel_get_duration(int index)
+-{
+- const struct mcs_group *group = &minstrel_mcs_groups[index / MCS_GROUP_RATES];
+- unsigned int duration = group->duration[index % MCS_GROUP_RATES];
+- return duration << group->shift;
+-}
+-
+ static void
+ minstrel_calc_retransmit(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
+ int index)
+@@ -988,14 +1159,18 @@ static void
+ minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
+ {
+ struct ieee80211_sta_rates *rates;
++ u16 first_rate = mi->max_tp_rate[0];
+ int i = 0;
+
++ if (mi->sample_mode == MINSTREL_SAMPLE_ACTIVE)
++ first_rate = mi->sample_rate;
++
+ 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]);
++ minstrel_ht_set_rate(mp, mi, rates, i++, first_rate);
+
+ if (mp->hw->max_rates >= 3) {
+ /* At least 3 tx rates supported, use max_tp_rate[1] next */
+@@ -1020,6 +1195,11 @@ minstrel_get_sample_rate(struct minstrel
+ int tp_rate1, tp_rate2;
+ int sample_idx = 0;
+
++ if (mp->hw->max_rates == 1 && mp->sample_switch &&
++ (mi->total_packets_cur >= SAMPLE_SWITCH_THR ||
++ mp->sample_switch == 1))
++ return -1;
++
+ if (mi->sample_wait > 0) {
+ mi->sample_wait--;
+ return -1;
+@@ -1341,7 +1521,7 @@ minstrel_ht_update_caps(void *priv, stru
+ mi->supported[MINSTREL_CCK_GROUP] |= mi->cck_supported_short << 4;
+
+ /* create an initial rate table with the lowest supported rates */
+- minstrel_ht_update_stats(mp, mi);
++ minstrel_ht_update_stats(mp, mi, true);
+ minstrel_ht_update_rates(mp, mi);
+
+ return;
+@@ -1459,6 +1639,8 @@ minstrel_ht_alloc(struct ieee80211_hw *h
+ if (!mp)
+ return NULL;
+
++ mp->sample_switch = -1;
++
+ /* contention window settings
+ * Just an approximation. Using the per-queue values would complicate
+ * the calculations and is probably unnecessary */
+@@ -1490,6 +1672,8 @@ minstrel_ht_alloc(struct ieee80211_hw *h
+ mp->fixed_rate_idx = (u32) -1;
+ debugfs_create_u32("fixed_rate_idx", S_IRUGO | S_IWUGO, debugfsdir,
+ &mp->fixed_rate_idx);
++ debugfs_create_u32("sample_switch", S_IRUGO | S_IWUSR, debugfsdir,
++ &mp->sample_switch);
+ #endif
+
+ minstrel_ht_init_cck_rates(mp);
+--- a/net/mac80211/rc80211_minstrel_ht.h
++++ b/net/mac80211/rc80211_minstrel_ht.h
+@@ -33,6 +33,7 @@ struct mcs_group {
+ u16 flags;
+ u8 streams;
+ u8 shift;
++ u8 bw;
+ u16 duration[MCS_GROUP_RATES];
+ };
+
+@@ -50,6 +51,12 @@ struct minstrel_mcs_group_data {
+ struct minstrel_rate_stats rates[MCS_GROUP_RATES];
+ };
+
++enum minstrel_sample_mode {
++ MINSTREL_SAMPLE_IDLE,
++ MINSTREL_SAMPLE_ACTIVE,
++ MINSTREL_SAMPLE_PENDING,
++};
++
+ struct minstrel_ht_sta {
+ struct ieee80211_sta *sta;
+
+@@ -71,6 +78,8 @@ struct minstrel_ht_sta {
+ unsigned int overhead;
+ unsigned int overhead_rtscts;
+
++ unsigned int total_packets_last;
++ unsigned int total_packets_cur;
+ unsigned int total_packets;
+ unsigned int sample_packets;
+
+@@ -82,6 +91,9 @@ struct minstrel_ht_sta {
+ u8 sample_count;
+ u8 sample_slow;
+
++ enum minstrel_sample_mode sample_mode;
++ u16 sample_rate;
++
+ /* current MCS group to be sampled */
+ u8 sample_group;
+
projects / openwrt / staging / ansuel.git / commitdiff