mac80211: minstrel_ht: significantly redesign the rate probing strategy

The biggest flaw in current minstrel_ht is the fact that it needs way too
many probing packets to be able to quickly find the best rate.
Depending on the wifi hardware and operating mode, this can significantly
reduce throughput when not operating at the highest available data rate.

In order to be able to significantly reduce the amount of rate sampling,
we need a much smarter selection of probing rates.

The new approach introduced by this patch maintains a limited set of
available rates to be tested during a statistics window.

They are split into distinct categories:
- MINSTREL_SAMPLE_TYPE_INC - incremental rate upgrade:
  Pick the next rate group and find the first rate that is faster than
  the current max. throughput rate
- MINSTREL_SAMPLE_TYPE_JUMP - random testing of higher rates:
  Pick a random rate from the next group that is faster than the current
  max throughput rate. This allows faster adaptation when the link changes
  significantly
- MINSTREL_SAMPLE_TYPE_SLOW - test a rate between max_prob, max_tp2 and
  max_tp in order to reduce the gap between them

In order to prioritize sampling, every 6 attempts are split into 3x INC,
2x JUMP, 1x SLOW.

Available rates are checked and refilled on every stats window update.

With this approach, we finally get a very small delta in throughput when
comparing setting the optimal data rate as a fixed rate vs normal rate
control operation.
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20210127055735.78599-4-nbd@nbd.nameSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rc80211_minstrel_ht.c

@@ -266,6 +266,14 @@ const struct mcs_group minstrel_mcs_groups[] = {
 const s16 minstrel_cck_bitrates[4] = { 10, 20, 55, 110 };
 const s16 minstrel_ofdm_bitrates[8] = { 60, 90, 120, 180, 240, 360, 480, 540 };
 static u8 sample_table[SAMPLE_COLUMNS][MCS_GROUP_RATES] __read_mostly;
+static const u8 minstrel_sample_seq[] = {
+	MINSTREL_SAMPLE_TYPE_INC,
+	MINSTREL_SAMPLE_TYPE_JUMP,
+	MINSTREL_SAMPLE_TYPE_INC,
+	MINSTREL_SAMPLE_TYPE_JUMP,
+	MINSTREL_SAMPLE_TYPE_INC,
+	MINSTREL_SAMPLE_TYPE_SLOW,
+};
 
 static void
 minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi);
@@ -620,77 +628,31 @@ minstrel_ht_prob_rate_reduce_streams(struct minstrel_ht_sta *mi)
 	}
 }
 
-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)
+static u16
+__minstrel_ht_get_sample_rate(struct minstrel_ht_sta *mi,
+			      enum minstrel_sample_type type)
 {
-	const struct mcs_group *group, *tp_group;
-	int i, g, max_dur;
-	int tp_idx;
-
-	tp_group = &minstrel_mcs_groups[MI_RATE_GROUP(mi->max_tp_rate[0])];
-	tp_idx = MI_RATE_IDX(mi->max_tp_rate[0]);
-
-	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;
+	u16 *rates = mi->sample[type].sample_rates;
+	u16 cur;
+	int i;
 
-		group = &minstrel_mcs_groups[g];
-		if (!minstrel_ht_probe_group(mi, tp_group, tp_idx, group))
+	for (i = 0; i < MINSTREL_SAMPLE_RATES; i++) {
+		if (!rates[i])
 			continue;
 
-		for (i = 0; supported; supported >>= 1, i++) {
-			int idx;
-
-			if (!(supported & 1))
-				continue;
-
-			if ((group->duration[i] << group->shift) > max_dur)
-				continue;
-
-			idx = MI_RATE(g, i);
-			if (idx == mi->max_tp_rate[0])
-				continue;
-
-			rates[(*n_rates)++] = idx;
-			break;
-		}
+		cur = rates[i];
+		rates[i] = 0;
+		return cur;
 	}
+
+	return 0;
 }
 
 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;
+	u16 rate;
 
 	/*
 	 * Use rate switching instead of probing packets for devices with
@@ -699,43 +661,11 @@ minstrel_ht_rate_sample_switch(struct minstrel_priv *mp,
 	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_avg > 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_RATE_GROUP(mi->max_tp_rate[0]);
-		u16 supported = mi->supported[g_idx];
-
-		supported >>= MI_RATE_IDX(mi->max_tp_rate[0]);
-		for (i = 0; supported; supported >>= 1, i++) {
-			if (!(supported & 1))
-				continue;
-
-			probe_rate = mi->max_tp_rate[0] + i;
-			goto out;
-		}
-
+	rate = __minstrel_ht_get_sample_rate(mi, MINSTREL_SAMPLE_TYPE_INC);
+	if (!rate)
 		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_rate = rate;
 	mi->sample_mode = MINSTREL_SAMPLE_ACTIVE;
 }
 
@@ -804,6 +734,274 @@ minstrel_ht_calc_rate_stats(struct minstrel_priv *mp,
 	mrs->attempts = 0;
 }
 
+static bool
+minstrel_ht_find_sample_rate(struct minstrel_ht_sta *mi, int type, int idx)
+{
+	int i;
+
+	for (i = 0; i < MINSTREL_SAMPLE_RATES; i++) {
+		u16 cur = mi->sample[type].sample_rates[i];
+
+		if (cur == idx)
+			return true;
+
+		if (!cur)
+			break;
+	}
+
+	return false;
+}
+
+static int
+minstrel_ht_move_sample_rates(struct minstrel_ht_sta *mi, int type,
+			      u32 fast_rate_dur, u32 slow_rate_dur)
+{
+	u16 *rates = mi->sample[type].sample_rates;
+	int i, j;
+
+	for (i = 0, j = 0; i < MINSTREL_SAMPLE_RATES; i++) {
+		u32 duration;
+		bool valid = false;
+		u16 cur;
+
+		cur = rates[i];
+		if (!cur)
+			continue;
+
+		duration = minstrel_get_duration(cur);
+		switch (type) {
+		case MINSTREL_SAMPLE_TYPE_SLOW:
+			valid = duration > fast_rate_dur &&
+				duration < slow_rate_dur;
+			break;
+		case MINSTREL_SAMPLE_TYPE_INC:
+		case MINSTREL_SAMPLE_TYPE_JUMP:
+			valid = duration < fast_rate_dur;
+			break;
+		default:
+			valid = false;
+			break;
+		}
+
+		if (!valid) {
+			rates[i] = 0;
+			continue;
+		}
+
+		if (i == j)
+			continue;
+
+		rates[j++] = cur;
+		rates[i] = 0;
+	}
+
+	return j;
+}
+
+static int
+minstrel_ht_group_min_rate_offset(struct minstrel_ht_sta *mi, int group,
+				  u32 max_duration)
+{
+	u16 supported = mi->supported[group];
+	int i;
+
+	for (i = 0; i < MCS_GROUP_RATES && supported; i++, supported >>= 1) {
+		if (!(supported & BIT(0)))
+			continue;
+
+		if (minstrel_get_duration(MI_RATE(group, i)) >= max_duration)
+			continue;
+
+		return i;
+	}
+
+	return -1;
+}
+
+/*
+ * Incremental update rates:
+ * Flip through groups and pick the first group rate that is faster than the
+ * highest currently selected rate
+ */
+static u16
+minstrel_ht_next_inc_rate(struct minstrel_ht_sta *mi, u32 fast_rate_dur)
+{
+	struct minstrel_mcs_group_data *mg;
+	u8 type = MINSTREL_SAMPLE_TYPE_INC;
+	int i, index = 0;
+	u8 group;
+
+	group = mi->sample[type].sample_group;
+	for (i = 0; i < ARRAY_SIZE(minstrel_mcs_groups); i++) {
+		group = (group + 1) % ARRAY_SIZE(minstrel_mcs_groups);
+		mg = &mi->groups[group];
+
+		index = minstrel_ht_group_min_rate_offset(mi, group,
+							  fast_rate_dur);
+		if (index < 0)
+			continue;
+
+		index = MI_RATE(group, index & 0xf);
+		if (!minstrel_ht_find_sample_rate(mi, type, index))
+			goto out;
+	}
+	index = 0;
+
+out:
+	mi->sample[type].sample_group = group;
+
+	return index;
+}
+
+static int
+minstrel_ht_next_group_sample_rate(struct minstrel_ht_sta *mi, int group,
+				   u16 supported, int offset)
+{
+	struct minstrel_mcs_group_data *mg = &mi->groups[group];
+	u16 idx;
+	int i;
+
+	for (i = 0; i < MCS_GROUP_RATES; i++) {
+		idx = sample_table[mg->column][mg->index];
+		if (++mg->index >= MCS_GROUP_RATES) {
+			mg->index = 0;
+			if (++mg->column >= ARRAY_SIZE(sample_table))
+				mg->column = 0;
+		}
+
+		if (idx < offset)
+			continue;
+
+		if (!(supported & BIT(idx)))
+			continue;
+
+		return MI_RATE(group, idx);
+	}
+
+	return -1;
+}
+
+/*
+ * Jump rates:
+ * Sample random rates, use those that are faster than the highest
+ * currently selected rate. Rates between the fastest and the slowest
+ * get sorted into the slow sample bucket, but only if it has room
+ */
+static u16
+minstrel_ht_next_jump_rate(struct minstrel_ht_sta *mi, u32 fast_rate_dur,
+			   u32 slow_rate_dur, int *slow_rate_ofs)
+{
+	struct minstrel_mcs_group_data *mg;
+	struct minstrel_rate_stats *mrs;
+	u32 max_duration = slow_rate_dur;
+	int i, index, offset;
+	u16 *slow_rates;
+	u16 supported;
+	u32 duration;
+	u8 group;
+
+	if (*slow_rate_ofs >= MINSTREL_SAMPLE_RATES)
+		max_duration = fast_rate_dur;
+
+	slow_rates = mi->sample[MINSTREL_SAMPLE_TYPE_SLOW].sample_rates;
+	group = mi->sample[MINSTREL_SAMPLE_TYPE_JUMP].sample_group;
+	for (i = 0; i < ARRAY_SIZE(minstrel_mcs_groups); i++) {
+		u8 type;
+
+		group = (group + 1) % ARRAY_SIZE(minstrel_mcs_groups);
+		mg = &mi->groups[group];
+
+		supported = mi->supported[group];
+		if (!supported)
+			continue;
+
+		offset = minstrel_ht_group_min_rate_offset(mi, group,
+							   max_duration);
+		if (offset < 0)
+			continue;
+
+		index = minstrel_ht_next_group_sample_rate(mi, group, supported,
+							   offset);
+		if (index < 0)
+			continue;
+
+		duration = minstrel_get_duration(index);
+		if (duration < fast_rate_dur)
+			type = MINSTREL_SAMPLE_TYPE_JUMP;
+		else
+			type = MINSTREL_SAMPLE_TYPE_SLOW;
+
+		if (minstrel_ht_find_sample_rate(mi, type, index))
+			continue;
+
+		if (type == MINSTREL_SAMPLE_TYPE_JUMP)
+			goto found;
+
+		if (*slow_rate_ofs >= MINSTREL_SAMPLE_RATES)
+			continue;
+
+		if (duration >= slow_rate_dur)
+			continue;
+
+		/* skip slow rates with high success probability */
+		mrs = minstrel_get_ratestats(mi, index);
+		if (mrs->prob_avg > MINSTREL_FRAC(95, 100))
+			continue;
+
+		slow_rates[(*slow_rate_ofs)++] = index;
+		if (*slow_rate_ofs >= MINSTREL_SAMPLE_RATES)
+			max_duration = fast_rate_dur;
+	}
+	index = 0;
+
+found:
+	mi->sample[MINSTREL_SAMPLE_TYPE_JUMP].sample_group = group;
+
+	return index;
+}
+
+static void
+minstrel_ht_refill_sample_rates(struct minstrel_ht_sta *mi)
+{
+	u32 prob_dur = minstrel_get_duration(mi->max_prob_rate);
+	u32 tp_dur = minstrel_get_duration(mi->max_tp_rate[0]);
+	u32 tp2_dur = minstrel_get_duration(mi->max_tp_rate[1]);
+	u32 fast_rate_dur = min(min(tp_dur, tp2_dur), prob_dur);
+	u32 slow_rate_dur = max(max(tp_dur, tp2_dur), prob_dur);
+	u16 *rates;
+	int i, j;
+
+	rates = mi->sample[MINSTREL_SAMPLE_TYPE_INC].sample_rates;
+	i = minstrel_ht_move_sample_rates(mi, MINSTREL_SAMPLE_TYPE_INC,
+					  fast_rate_dur, slow_rate_dur);
+	while (i < MINSTREL_SAMPLE_RATES) {
+		rates[i] = minstrel_ht_next_inc_rate(mi, tp_dur);
+		if (!rates[i])
+			break;
+
+		i++;
+	}
+
+	rates = mi->sample[MINSTREL_SAMPLE_TYPE_JUMP].sample_rates;
+	i = minstrel_ht_move_sample_rates(mi, MINSTREL_SAMPLE_TYPE_JUMP,
+					  fast_rate_dur, slow_rate_dur);
+	j = minstrel_ht_move_sample_rates(mi, MINSTREL_SAMPLE_TYPE_SLOW,
+					  fast_rate_dur, slow_rate_dur);
+	while (i < MINSTREL_SAMPLE_RATES) {
+		rates[i] = minstrel_ht_next_jump_rate(mi, fast_rate_dur,
+						      slow_rate_dur, &j);
+		if (!rates[i])
+			break;
+
+		i++;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(mi->sample); i++)
+		memcpy(mi->sample[i].cur_sample_rates, mi->sample[i].sample_rates,
+		       sizeof(mi->sample[i].cur_sample_rates));
+}
+
+
 /*
  * Update rate statistics and select new primary rates
  *
@@ -848,8 +1046,6 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
 		mi->ampdu_packets = 0;
 	}
 
-	mi->sample_count = 0;
-
 	if (mi->supported[MINSTREL_CCK_GROUP])
 		group = MINSTREL_CCK_GROUP;
 	else if (mi->supported[MINSTREL_OFDM_GROUP])
@@ -884,8 +1080,6 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
 		if (!mi->supported[group])
 			continue;
 
-		mi->sample_count++;
-
 		/* (re)Initialize group rate indexes */
 		for(j = 0; j < MAX_THR_RATES; j++)
 			tmp_group_tp_rate[j] = MI_RATE(group, 0);
@@ -952,9 +1146,7 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
 
 	/* Try to increase robustness of max_prob_rate*/
 	minstrel_ht_prob_rate_reduce_streams(mi);
-
-	/* try to sample half of all available rates during each interval */
-	mi->sample_count *= 4;
+	minstrel_ht_refill_sample_rates(mi);
 
 	if (sample)
 		minstrel_ht_rate_sample_switch(mp, mi);
@@ -971,6 +1163,7 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
 
 	/* Reset update timer */
 	mi->last_stats_update = jiffies;
+	mi->sample_time = jiffies;
 }
 
 static bool
@@ -1000,28 +1193,6 @@ minstrel_ht_txstat_valid(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
 	return false;
 }
 
-static void
-minstrel_set_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 (!mi->supported[mi->sample_group])
-			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)
 {
@@ -1107,14 +1278,6 @@ minstrel_ht_tx_status(void *priv, struct ieee80211_supported_band *sband,
 	mi->ampdu_packets++;
 	mi->ampdu_len += info->status.ampdu_len;
 
-	if (!mi->sample_wait && !mi->sample_tries && mi->sample_count > 0) {
-		int avg_ampdu_len = minstrel_ht_avg_ampdu_len(mi);
-
-		mi->sample_wait = 16 + 2 * avg_ampdu_len;
-		mi->sample_tries = 1;
-		mi->sample_count--;
-	}
-
 	if (mi->sample_mode != MINSTREL_SAMPLE_IDLE)
 		rate_sample = minstrel_get_ratestats(mi, mi->sample_rate);
 
@@ -1386,97 +1549,20 @@ minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
 	rate_control_set_rates(mp->hw, mi->sta, rates);
 }
 
-static int
-minstrel_get_sample_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
+static u16
+minstrel_ht_get_sample_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
 {
-	struct minstrel_rate_stats *mrs;
-	struct minstrel_mcs_group_data *mg;
-	unsigned int sample_dur, sample_group, cur_max_tp_streams;
-	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;
+	u8 seq;
 
-	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_set_next_sample_idx(mi);
-
-	if (!(mi->supported[sample_group] & BIT(sample_idx)))
-		return -1;
-
-	mrs = &mg->rates[sample_idx];
-	sample_idx += MI_RATE(sample_group, 0);
-
-	tp_rate1 = mi->max_tp_rate[0];
-
-	/* Set tp_rate2 to the second highest max_tp_rate */
-	if (minstrel_get_duration(mi->max_tp_rate[0]) >
-	    minstrel_get_duration(mi->max_tp_rate[1])) {
-		tp_rate2 = mi->max_tp_rate[0];
+	if (mp->hw->max_rates > 1) {
+		seq = mi->sample_seq;
+		mi->sample_seq = (seq + 1) % ARRAY_SIZE(minstrel_sample_seq);
+		seq = minstrel_sample_seq[seq];
 	} else {
-		tp_rate2 = mi->max_tp_rate[1];
+		seq = MINSTREL_SAMPLE_TYPE_INC;
 	}
 
-	/*
-	 * Sampling might add some overhead (RTS, no aggregation)
-	 * to the frame. Hence, don't use sampling for the highest currently
-	 * used highest throughput or probability rate.
-	 */
-	if (sample_idx == mi->max_tp_rate[0] || sample_idx == mi->max_prob_rate)
-		return -1;
-
-	/*
-	 * Do not sample if the probability is already higher than 95%,
-	 * or if the rate is 3 times slower than the current max probability
-	 * rate, to avoid wasting airtime.
-	 */
-	sample_dur = minstrel_get_duration(sample_idx);
-	if (mrs->prob_avg > MINSTREL_FRAC(95, 100) ||
-	    minstrel_get_duration(mi->max_prob_rate) * 3 < sample_dur)
-		return -1;
-
-
-	/*
-	 * For devices with no configurable multi-rate retry, skip sampling
-	 * below the per-group max throughput rate, and only use one sampling
-	 * attempt per rate
-	 */
-	if (mp->hw->max_rates == 1 &&
-	    (minstrel_get_duration(mg->max_group_tp_rate[0]) < sample_dur ||
-	     mrs->attempts))
-		return -1;
-
-	/* Skip already sampled slow rates */
-	if (sample_dur >= minstrel_get_duration(tp_rate1) && mrs->attempts)
-		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_RATE_GROUP(tp_rate1)].streams;
-	if (sample_dur >= minstrel_get_duration(tp_rate2) &&
-	    (cur_max_tp_streams - 1 <
-	     minstrel_mcs_groups[sample_group].streams ||
-	     sample_dur >= minstrel_get_duration(mi->max_prob_rate)))
-			return -1;
-
-	mi->sample_tries--;
-
-	return sample_idx;
+	return __minstrel_ht_get_sample_rate(mi, seq);
 }
 
 static void
@@ -1488,7 +1574,7 @@ minstrel_ht_get_rate(void *priv, struct ieee80211_sta *sta, void *priv_sta,
 	struct ieee80211_tx_rate *rate = &info->status.rates[0];
 	struct minstrel_ht_sta *mi = priv_sta;
 	struct minstrel_priv *mp = priv;
-	int sample_idx;
+	u16 sample_idx;
 
 	if (!(info->flags & IEEE80211_TX_CTL_AMPDU) &&
 	    !minstrel_ht_is_legacy_group(MI_RATE_GROUP(mi->max_prob_rate)))
@@ -1504,11 +1590,19 @@ minstrel_ht_get_rate(void *priv, struct ieee80211_sta *sta, void *priv_sta,
 	/* 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);
+		return;
+
+	if (mp->hw->max_rates == 1 && mp->sample_switch &&
+	    (mi->total_packets_cur >= SAMPLE_SWITCH_THR ||
+	     mp->sample_switch == 1))
+		return;
+
+	if (time_is_before_jiffies(mi->sample_time))
+		return;
 
-	if (sample_idx < 0)
+	mi->sample_time = jiffies + MINSTREL_SAMPLE_INTERVAL;
+	sample_idx = minstrel_ht_get_sample_rate(mp, mi);
+	if (!sample_idx)
 		return;
 
 	sample_group = &minstrel_mcs_groups[MI_RATE_GROUP(sample_idx)];
@@ -1629,16 +1723,6 @@ minstrel_ht_update_caps(void *priv, struct ieee80211_supported_band *sband,
 
 	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;
-
 	if (!use_vht) {
 		stbc = (ht_cap & IEEE80211_HT_CAP_RX_STBC) >>
 			IEEE80211_HT_CAP_RX_STBC_SHIFT;

net/mac80211/rc80211_minstrel_ht.h

@@ -69,6 +69,8 @@
 #define MI_RATE_IDX(_rate) FIELD_GET(MI_RATE_IDX_MASK, _rate)
 #define MI_RATE_GROUP(_rate) FIELD_GET(MI_RATE_GROUP_MASK, _rate)
 
+#define MINSTREL_SAMPLE_RATES		5 /* rates per sample type */
+#define MINSTREL_SAMPLE_INTERVAL	(HZ / 50)
 
 struct minstrel_priv {
 	struct ieee80211_hw *hw;
@@ -126,6 +128,13 @@ struct minstrel_rate_stats {
 	bool retry_updated;
 };
 
+enum minstrel_sample_type {
+	MINSTREL_SAMPLE_TYPE_INC,
+	MINSTREL_SAMPLE_TYPE_JUMP,
+	MINSTREL_SAMPLE_TYPE_SLOW,
+	__MINSTREL_SAMPLE_TYPE_MAX
+};
+
 struct minstrel_mcs_group_data {
 	u8 index;
 	u8 column;
@@ -144,6 +153,12 @@ enum minstrel_sample_mode {
 	MINSTREL_SAMPLE_PENDING,
 };
 
+struct minstrel_sample_category {
+	u8 sample_group;
+	u16 sample_rates[MINSTREL_SAMPLE_RATES];
+	u16 cur_sample_rates[MINSTREL_SAMPLE_RATES];
+};
+
 struct minstrel_ht_sta {
 	struct ieee80211_sta *sta;
 
@@ -175,16 +190,14 @@ struct minstrel_ht_sta {
 	/* tx flags to add for frames for this sta */
 	u32 tx_flags;
 
-	u8 sample_wait;
-	u8 sample_tries;
-	u8 sample_count;
+	unsigned long sample_time;
+	struct minstrel_sample_category sample[__MINSTREL_SAMPLE_TYPE_MAX];
+
+	u8 sample_seq;
 
 	enum minstrel_sample_mode sample_mode;
 	u16 sample_rate;
 
-	/* current MCS group to be sampled */
-	u8 sample_group;
-
 	u8 band;
 
 	/* Bitfield of supported MCS rates of all groups */