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@@ -0,0 +1,151 @@
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+From: Felix Fietkau <[email protected]>
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+Date: Sat, 6 Feb 2021 16:33:14 +0100
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+Subject: [PATCH] mac80211: minstrel_ht: rework rate downgrade code and
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+ max_prob rate selection
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+
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+The current fallback code for fast rate switching on potentially failing rates
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+is triggering too often if there is some strong noise on the channel. This can
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+lead to wild fluctuations in the rate selection.
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+Additionally, switching down to max_prob_rate can create a significant gap down
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+in throughput, especially when using only 2 spatial streams, because max_prob_rate
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+is limited to using fewer streams than the max_tp rates.
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+In order to improve throughput without reducing reliability too much, use the
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+rate downgrade code for the max_prob_rate only, and allow the non-downgraded
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+max_prob_rate to use as many spatial streams as the max_tp rates
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+
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+Signed-off-by: Felix Fietkau <[email protected]>
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+---
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+
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+--- a/net/mac80211/rc80211_minstrel_ht.c
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++++ b/net/mac80211/rc80211_minstrel_ht.c
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+@@ -511,6 +511,14 @@ minstrel_ht_set_best_prob_rate(struct mi
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+ int cur_tp_avg, cur_group, cur_idx;
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+ int max_gpr_group, max_gpr_idx;
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+ int max_gpr_tp_avg, max_gpr_prob;
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++ int min_dur;
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++
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++ min_dur = max(minstrel_get_duration(mi->max_tp_rate[0]),
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++ minstrel_get_duration(mi->max_tp_rate[1]));
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++
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++ /* make the rate at least 18% slower than max tp rates */
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++ if (minstrel_get_duration(index) <= min_dur * 19 / 16)
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++ return;
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+
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+ cur_group = MI_RATE_GROUP(index);
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+ cur_idx = MI_RATE_IDX(index);
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+@@ -532,11 +540,6 @@ minstrel_ht_set_best_prob_rate(struct mi
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+ !minstrel_ht_is_legacy_group(max_tp_group))
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+ return;
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+
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+- /* skip rates faster than max tp rate with lower prob */
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+- if (minstrel_get_duration(mi->max_tp_rate[0]) > minstrel_get_duration(index) &&
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+- mrs->prob_avg < max_tp_prob)
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+- return;
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+-
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+ max_gpr_group = MI_RATE_GROUP(mg->max_group_prob_rate);
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+ max_gpr_idx = MI_RATE_IDX(mg->max_group_prob_rate);
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+ max_gpr_prob = mi->groups[max_gpr_group].rates[max_gpr_idx].prob_avg;
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+@@ -594,40 +597,6 @@ minstrel_ht_assign_best_tp_rates(struct
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+
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+ }
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+
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+-/*
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+- * Try to increase robustness of max_prob rate by decrease number of
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+- * streams if possible.
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+- */
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+-static inline void
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+-minstrel_ht_prob_rate_reduce_streams(struct minstrel_ht_sta *mi)
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+-{
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+- struct minstrel_mcs_group_data *mg;
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+- int tmp_max_streams, group, tmp_idx, tmp_prob;
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+- int tmp_tp = 0;
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+-
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+- if (!mi->sta->ht_cap.ht_supported)
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+- return;
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+-
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+- group = MI_RATE_GROUP(mi->max_tp_rate[0]);
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+- tmp_max_streams = minstrel_mcs_groups[group].streams;
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+- for (group = 0; group < ARRAY_SIZE(minstrel_mcs_groups); group++) {
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+- mg = &mi->groups[group];
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+- if (!mi->supported[group] || group == MINSTREL_CCK_GROUP)
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+- continue;
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+-
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+- tmp_idx = MI_RATE_IDX(mg->max_group_prob_rate);
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+- tmp_prob = mi->groups[group].rates[tmp_idx].prob_avg;
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+-
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+- if (tmp_tp < minstrel_ht_get_tp_avg(mi, group, tmp_idx, tmp_prob) &&
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+- (minstrel_mcs_groups[group].streams < tmp_max_streams)) {
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+- mi->max_prob_rate = mg->max_group_prob_rate;
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+- tmp_tp = minstrel_ht_get_tp_avg(mi, group,
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+- tmp_idx,
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+- tmp_prob);
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+- }
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+- }
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+-}
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+-
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+ static u16
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+ __minstrel_ht_get_sample_rate(struct minstrel_ht_sta *mi,
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+ enum minstrel_sample_type type)
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+@@ -1111,8 +1080,6 @@ minstrel_ht_update_stats(struct minstrel
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+
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+ mi->max_prob_rate = tmp_max_prob_rate;
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+
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+- /* Try to increase robustness of max_prob_rate*/
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+- minstrel_ht_prob_rate_reduce_streams(mi);
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+ minstrel_ht_refill_sample_rates(mi);
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+
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+ #ifdef CPTCFG_MAC80211_DEBUGFS
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+@@ -1157,7 +1124,7 @@ minstrel_ht_txstat_valid(struct minstrel
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+ }
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+
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+ static void
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+-minstrel_downgrade_rate(struct minstrel_ht_sta *mi, u16 *idx, bool primary)
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++minstrel_downgrade_prob_rate(struct minstrel_ht_sta *mi, u16 *idx)
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+ {
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+ int group, orig_group;
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+
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+@@ -1172,11 +1139,7 @@ minstrel_downgrade_rate(struct minstrel_
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+ minstrel_mcs_groups[orig_group].streams)
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+ continue;
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+
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+- if (primary)
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+- *idx = mi->groups[group].max_group_tp_rate[0];
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+- else
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+- *idx = mi->groups[group].max_group_tp_rate[1];
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+- break;
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++ *idx = mi->groups[group].max_group_prob_rate;
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+ }
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+ }
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+
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+@@ -1210,7 +1173,7 @@ minstrel_ht_tx_status(void *priv, struct
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+ struct ieee80211_tx_info *info = st->info;
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+ struct minstrel_ht_sta *mi = priv_sta;
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+ struct ieee80211_tx_rate *ar = info->status.rates;
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+- struct minstrel_rate_stats *rate, *rate2;
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++ struct minstrel_rate_stats *rate;
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+ struct minstrel_priv *mp = priv;
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+ u32 update_interval = mp->update_interval;
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+ bool last, update = false;
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+@@ -1256,18 +1219,13 @@ minstrel_ht_tx_status(void *priv, struct
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+ /*
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+ * check for sudden death of spatial multiplexing,
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+ * downgrade to a lower number of streams if necessary.
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++ * only do this for the max_prob_rate to prevent spurious
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++ * rate fluctuations when the link changes suddenly
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+ */
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+- rate = minstrel_get_ratestats(mi, mi->max_tp_rate[0]);
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++ rate = minstrel_get_ratestats(mi, mi->max_prob_rate);
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+ if (rate->attempts > 30 &&
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+ rate->success < rate->attempts / 4) {
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+- minstrel_downgrade_rate(mi, &mi->max_tp_rate[0], true);
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+- update = true;
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+- }
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+-
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+- rate2 = minstrel_get_ratestats(mi, mi->max_tp_rate[1]);
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+- if (rate2->attempts > 30 &&
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+- rate2->success < rate2->attempts / 4) {
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+- minstrel_downgrade_rate(mi, &mi->max_tp_rate[1], false);
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++ minstrel_downgrade_prob_rate(mi, &mi->max_prob_rate);
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+ update = true;
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+ }
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+ }
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Felix Fietkau