[PATCH 0/7] mac80211: improve and consolidate minstrel rate control

[PATCH 0/7] mac80211: improve and consolidate minstrel rate control

[Thomas Huehn]

This patch series merges functions, macros and sampling improvements from
minstrel_ht into minstrel. It adds several improvements to the rate control.  

Thomas

[PATCH 1/7] mac80211: merge EWMA calculation of minstrel_ht and minstrel

[Thomas Huehn]

Both rate control algorithms (minstrel and minstrel_ht) calculate
averages based on EWMA. Shift function minstrel_ewma() into
rc80211_minstrel.h and make use of it in both minstrel version.
Also shift the default EWMA level (75%) definition to the header file
and clean up variable usage.

Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
---
 net/mac80211/rc80211_minstrel.c    | 15 +++++----------
 net/mac80211/rc80211_minstrel.h    | 13 ++++++++++++-
 net/mac80211/rc80211_minstrel_ht.c | 10 ----------
 3 files changed, 17 insertions(+), 21 deletions(-)

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index eea45a2..d78f629 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -76,7 +76,6 @@ 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;
@@ -90,14 +89,13 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 		/* To avoid rounding issues, probabilities scale from 0 (0%)
 		 * to 18000 (100%) */
 		if (mr->attempts) {
-			p = (mr->success * 18000) / mr->attempts;
+			mr->cur_prob = (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->probability = minstrel_ewma(mr->probability,
+							mr->cur_prob,
+							EWMA_LEVEL);
+			mr->cur_tp = mr->probability * (1000000 / usecs);
 		}
 
 		mr->last_success = mr->success;
@@ -542,9 +540,6 @@ minstrel_alloc(struct ieee80211_hw *hw, struct dentry *debugfsdir)
 	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;
 
diff --git a/net/mac80211/rc80211_minstrel.h b/net/mac80211/rc80211_minstrel.h
index 5ecf757..98db93f 100644
--- a/net/mac80211/rc80211_minstrel.h
+++ b/net/mac80211/rc80211_minstrel.h
@@ -9,6 +9,18 @@
 #ifndef __RC_MINSTREL_H
 #define __RC_MINSTREL_H
 
+#define EWMA_LEVEL 75	/* ewma weighting factor [%] */
+
+/*
+ * Perform EWMA (Exponentially Weighted Moving Average) calculation
+  */
+static inline int
+minstrel_ewma(int old, int new, int weight)
+{
+	return (new * (100 - weight) + old * weight) / 100;
+}
+
+
 struct minstrel_rate {
 	int bitrate;
 	int rix;
@@ -73,7 +85,6 @@ struct minstrel_priv {
 	unsigned int cw_min;
 	unsigned int cw_max;
 	unsigned int max_retry;
-	unsigned int ewma_level;
 	unsigned int segment_size;
 	unsigned int update_interval;
 	unsigned int lookaround_rate;
diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
index 3af141c..a3081e5 100644
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -18,7 +18,6 @@
 
 #define AVG_PKT_SIZE	1200
 #define SAMPLE_COLUMNS	10
-#define EWMA_LEVEL		75
 
 /* Number of bits for an average sized packet */
 #define MCS_NBITS (AVG_PKT_SIZE << 3)
@@ -129,15 +128,6 @@ const struct mcs_group minstrel_mcs_groups[] = {
 static u8 sample_table[SAMPLE_COLUMNS][MCS_GROUP_RATES];
 
 /*
- * Perform EWMA (Exponentially Weighted Moving Average) calculation
- */
-static int
-minstrel_ewma(int old, int new, int weight)
-{
-	return (new * (100 - weight) + old * weight) / 100;
-}
-
-/*
  * Look up an MCS group index based on mac80211 rate information
  */
 static int
-- 
1.8.1.1

[PATCH 2/7] mac80211: merge value scaling macros of minstrel_ht and minstrel

[Thomas Huehn]

Both minstrel versions use individual ways to scale up integer values
to perform calculations. Merge minstrel_ht's scaling macros into
minstrels header file and use them in both minstrel versions.

Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
---
 net/mac80211/rc80211_minstrel.c         | 9 ++++-----
 net/mac80211/rc80211_minstrel.h         | 5 +++++
 net/mac80211/rc80211_minstrel_debugfs.c | 6 +++---
 net/mac80211/rc80211_minstrel_ht.h      | 5 -----
 4 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index d78f629..c9b9902 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -86,10 +86,8 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 		if (!usecs)
 			usecs = 1000000;
 
-		/* To avoid rounding issues, probabilities scale from 0 (0%)
-		 * to 18000 (100%) */
 		if (mr->attempts) {
-			mr->cur_prob = (mr->success * 18000) / mr->attempts;
+			mr->cur_prob = MINSTREL_FRAC(mr->success, mr->attempts);
 			mr->succ_hist += mr->success;
 			mr->att_hist += mr->attempts;
 			mr->probability = minstrel_ewma(mr->probability,
@@ -105,7 +103,8 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 
 		/* 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)) {
+		if (mr->probability > MINSTREL_FRAC(95, 100) ||
+		    mr->probability < MINSTREL_FRAC(10, 100)) {
 			mr->adjusted_retry_count = mr->retry_count >> 1;
 			if (mr->adjusted_retry_count > 2)
 				mr->adjusted_retry_count = 2;
@@ -300,7 +299,7 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
 	/* 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))
+	if (!mrr && sample && (mi->r[ndx].probability > MINSTREL_FRAC(95, 100)))
 		ndx = mi->max_tp_rate;
 
 	ar[0].idx = mi->r[ndx].rix;
diff --git a/net/mac80211/rc80211_minstrel.h b/net/mac80211/rc80211_minstrel.h
index 98db93f..fda4a61 100644
--- a/net/mac80211/rc80211_minstrel.h
+++ b/net/mac80211/rc80211_minstrel.h
@@ -11,6 +11,11 @@
 
 #define EWMA_LEVEL 75	/* ewma weighting factor [%] */
 
+/* scaled fraction values */
+#define MINSTREL_SCALE  16
+#define MINSTREL_FRAC(val, div) (((val) << MINSTREL_SCALE) / div)
+#define MINSTREL_TRUNC(val) ((val) >> MINSTREL_SCALE)
+
 /*
  * Perform EWMA (Exponentially Weighted Moving Average) calculation
   */
diff --git a/net/mac80211/rc80211_minstrel_debugfs.c b/net/mac80211/rc80211_minstrel_debugfs.c
index d5a5622..c0ebfac 100644
--- a/net/mac80211/rc80211_minstrel_debugfs.c
+++ b/net/mac80211/rc80211_minstrel_debugfs.c
@@ -79,9 +79,9 @@ minstrel_stats_open(struct inode *inode, struct file *file)
 		p += sprintf(p, "%3u%s", mr->bitrate / 2,
 				(mr->bitrate & 1 ? ".5" : "  "));
 
-		tp = mr->cur_tp / ((18000 << 10) / 96);
-		prob = mr->cur_prob / 18;
-		eprob = mr->probability / 18;
+		tp = MINSTREL_TRUNC(mr->cur_tp / 10);
+		prob = MINSTREL_TRUNC(mr->cur_prob * 1000);
+		eprob = MINSTREL_TRUNC(mr->probability * 1000);
 
 		p += sprintf(p, "  %6u.%1u   %6u.%1u   %6u.%1u        "
 				"%3u(%3u)   %8llu    %8llu\n",
diff --git a/net/mac80211/rc80211_minstrel_ht.h b/net/mac80211/rc80211_minstrel_ht.h
index 302dbd5..4ee5999 100644
--- a/net/mac80211/rc80211_minstrel_ht.h
+++ b/net/mac80211/rc80211_minstrel_ht.h
@@ -16,11 +16,6 @@
 #define MINSTREL_MAX_STREAMS	3
 #define MINSTREL_STREAM_GROUPS	4
 
-/* scaled fraction values */
-#define MINSTREL_SCALE	16
-#define MINSTREL_FRAC(val, div) (((val) << MINSTREL_SCALE) / div)
-#define MINSTREL_TRUNC(val) ((val) >> MINSTREL_SCALE)
-
 #define MCS_GROUP_RATES	8
 
 struct mcs_group {
-- 
1.8.1.1

[PATCH 3/7] mac80211: add documentation and verbose variable names in

[Thomas Huehn]

Add documentation and more verbose variable names to minstrel's
multi-rate-retry setup within function minstrel_get_rate() to
increase the readability of the algorithm.

Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
---
 net/mac80211/rc80211_minstrel.c | 81 +++++++++++++++++++++++++----------------
 net/mac80211/rc80211_minstrel.h |  2 +-
 2 files changed, 50 insertions(+), 33 deletions(-)

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index c9b9902..152bb0e 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -78,7 +78,6 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 	u32 usecs;
 	int i;
 
-	mi->stats_update = jiffies;
 	for (i = 0; i < mi->n_rates; i++) {
 		struct minstrel_rate *mr = &mi->r[i];
 
@@ -144,6 +143,9 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 	mi->max_tp_rate = index_max_tp;
 	mi->max_tp_rate2 = index_max_tp2;
 	mi->max_prob_rate = index_max_prob;
+
+	/* Reset update timer */
+	mi->stats_update = jiffies;
 }
 
 static void
@@ -204,10 +206,10 @@ 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;
+	sample_ndx = SAMPLE_TBL(mi, mi->sample_row, mi->sample_column);
+	mi->sample_row++;
+	if ((int) mi->sample_row > (mi->n_rates - 2)) {
+		mi->sample_row = 0;
 		mi->sample_column++;
 		if (mi->sample_column >= SAMPLE_COLUMNS)
 			mi->sample_column = 0;
@@ -225,31 +227,37 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *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;
+	bool mrr_capable;
+	bool indirect_rate_sampling = false;
+	bool rate_sampling = false;
 	int i, delta;
 	int mrr_ndx[3];
-	int sample_rate;
+	int sampling_ratio;
 
+	/* management/no-ack frames do not use rate control */
 	if (rate_control_send_low(sta, priv_sta, txrc))
 		return;
 
-	mrr = mp->has_mrr && !txrc->rts && !txrc->bss_conf->use_cts_prot;
+	/* check multi-rate-retry capabilities & adjust lookaround_rate */
+	mrr_capable = mp->has_mrr &&
+		      !txrc->rts &&
+		      !txrc->bss_conf->use_cts_prot;
+	if (mrr_capable)
+		sampling_ratio = mp->lookaround_rate_mrr;
+	else
+		sampling_ratio = mp->lookaround_rate;
 
+	/* init rateindex [ndx] with max throughput rate */
 	ndx = mi->max_tp_rate;
 
-	if (mrr)
-		sample_rate = mp->lookaround_rate_mrr;
-	else
-		sample_rate = mp->lookaround_rate;
-
+	/* increase sum packet counter */
 	mi->packet_count++;
-	delta = (mi->packet_count * sample_rate / 100) -
+
+	delta = (mi->packet_count * sampling_ratio / 100) -
 			(mi->sample_count + mi->sample_deferred / 2);
 
 	/* delta > 0: sampling required */
-	if ((delta > 0) && (mrr || !mi->prev_sample)) {
+	if ((delta > 0) && (mrr_capable || !mi->prev_sample)) {
 		struct minstrel_rate *msr;
 		if (mi->packet_count >= 10000) {
 			mi->sample_deferred = 0;
@@ -268,21 +276,25 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
 			mi->sample_count += (delta - mi->n_rates * 2);
 		}
 
+		/* get next random rate sample */
 		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);
+		rate_sampling = true;
 
-		if (!sample_slower) {
+		/* Decide if direct ( 1st mrr stage) or indirect (2nd mrr stage)
+		 * rate sampling method should be used */
+		if (mrr_capable &&
+		    msr->perfect_tx_time > mi->r[ndx].perfect_tx_time)
+				indirect_rate_sampling = true;
+
+		if (!indirect_rate_sampling) {
 			if (msr->sample_limit != 0) {
 				ndx = sample_ndx;
 				mi->sample_count++;
 				if (msr->sample_limit > 0)
 					msr->sample_limit--;
-			} else {
-				sample = false;
-			}
+			} else
+				rate_sampling = false;
 		} else {
 			/* Only use IEEE80211_TX_CTL_RATE_CTRL_PROBE to mark
 			 * packets that have the sampling rate deferred to the
@@ -294,34 +306,39 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
 			mi->sample_deferred++;
 		}
 	}
-	mi->prev_sample = sample;
+	mi->prev_sample = rate_sampling;
 
 	/* 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 > MINSTREL_FRAC(95, 100)))
+	if (!mrr_capable && rate_sampling &&
+	   (mi->r[ndx].probability > MINSTREL_FRAC(95, 100)))
 		ndx = mi->max_tp_rate;
 
+	/* mrr setup for 1st stage */
 	ar[0].idx = mi->r[ndx].rix;
 	ar[0].count = minstrel_get_retry_count(&mi->r[ndx], info);
 
-	if (!mrr) {
-		if (!sample)
+	/* non mrr setup for 2nd stage */
+	if (!mrr_capable) {
+		if (!rate_sampling)
 			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 setup for 2nd stage */
+	if (rate_sampling) {
+		if (indirect_rate_sampling)
 			mrr_ndx[0] = sample_ndx;
 		else
 			mrr_ndx[0] = mi->max_tp_rate;
 	} else {
 		mrr_ndx[0] = mi->max_tp_rate2;
 	}
+
+	/* mrr setup for 3rd & 4th stage */
 	mrr_ndx[1] = mi->max_prob_rate;
 	mrr_ndx[2] = 0;
 	for (i = 1; i < 4; i++) {
@@ -352,7 +369,7 @@ init_sample_table(struct minstrel_sta_info *mi)
 	u8 rnd[8];
 
 	mi->sample_column = 0;
-	mi->sample_idx = 0;
+	mi->sample_row = 0;
 	memset(mi->sample_table, 0, SAMPLE_COLUMNS * mi->n_rates);
 
 	for (col = 0; col < SAMPLE_COLUMNS; col++) {
diff --git a/net/mac80211/rc80211_minstrel.h b/net/mac80211/rc80211_minstrel.h
index fda4a61..5fb5cb8 100644
--- a/net/mac80211/rc80211_minstrel.h
+++ b/net/mac80211/rc80211_minstrel.h
@@ -69,7 +69,7 @@ struct minstrel_sta_info {
 	unsigned int sample_count;
 	int sample_deferred;
 
-	unsigned int sample_idx;
+	unsigned int sample_row;
 	unsigned int sample_column;
 
 	int n_rates;
-- 
1.8.1.1

[PATCH 4/7] mac80211: extend minstrel's rate sampling to avoid unsampled rates

[Thomas Huehn]

Minstrel's decision which rate should be directly sampled within the
1st mrr stage is limited to such rates faster than the current max
throughput rate. All rates below the current max. throughput rate
are indirectly sampled via the 2nd mrr stage.
This approach leads to deprecated per rate statistics and therfore
a deprecated mrr chain setup.

This patch uses the sampling approach from minstrel_ht. A counter is
added to sum all indirect sample attempts per rate. After 20 indirect
sampling attempts the rate is directly sampled within the 1st mrr stage.
Therefore more up-to-date statistics for all rates are maintained and
used to setup the mrr chain.

Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
---
 net/mac80211/rc80211_minstrel.c | 13 +++++++++----
 net/mac80211/rc80211_minstrel.h |  1 +
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index 152bb0e..aa59f29 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -85,7 +85,8 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 		if (!usecs)
 			usecs = 1000000;
 
-		if (mr->attempts) {
+		if (unlikely(mr->attempts > 0)) {
+			mr->sample_skipped = 0;
 			mr->cur_prob = MINSTREL_FRAC(mr->success, mr->attempts);
 			mr->succ_hist += mr->success;
 			mr->att_hist += mr->attempts;
@@ -93,7 +94,8 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 							mr->cur_prob,
 							EWMA_LEVEL);
 			mr->cur_tp = mr->probability * (1000000 / usecs);
-		}
+		} else
+			mr->sample_skipped++;
 
 		mr->last_success = mr->success;
 		mr->last_attempts = mr->attempts;
@@ -282,9 +284,12 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
 		rate_sampling = true;
 
 		/* Decide if direct ( 1st mrr stage) or indirect (2nd mrr stage)
-		 * rate sampling method should be used */
+		 * rate sampling method should be used.
+		 * Respect such rates that are not sampled for 20 interations.
+		 */
 		if (mrr_capable &&
-		    msr->perfect_tx_time > mi->r[ndx].perfect_tx_time)
+		    msr->perfect_tx_time > mi->r[ndx].perfect_tx_time &&
+		    msr->sample_skipped < 20)
 				indirect_rate_sampling = true;
 
 		if (!indirect_rate_sampling) {
diff --git a/net/mac80211/rc80211_minstrel.h b/net/mac80211/rc80211_minstrel.h
index 5fb5cb8..200b7e3 100644
--- a/net/mac80211/rc80211_minstrel.h
+++ b/net/mac80211/rc80211_minstrel.h
@@ -43,6 +43,7 @@ struct minstrel_rate {
 	u32 attempts;
 	u32 last_attempts;
 	u32 last_success;
+	u8 sample_skipped;
 
 	/* parts per thousand */
 	u32 cur_prob;
-- 
1.8.1.1

[PATCH 5/7] mac80211: add lowest rate into minstrel's randmon rate sampling table

[Thomas Huehn]

While minstrel bootstraps and fills the success probabilities of each
rate the lowest rate has typically a very high success probability
(often 100% in our tests).
Its statistics are never updated but considered to setup the mrr chain.
In our tests we see that especially the 3rd mrr stage (which is that
rate providing highest success probability) is filled with the lowest rate
because its initial high sucess probability is never updated. By design
the 4th mrr stage is filled with the lowest rate so often 3rd and 4th
mrr stage are equal.

This patch follows minstrels general approach of assuming as little
as possible about rate dependencies. Consequently we include the
lowest rate into the random sampling table to get balanced up-to-date
statistics of all rates and therefore balanced decisions.

Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
---
 net/mac80211/rc80211_minstrel.c    | 22 ++++++++--------------
 net/mac80211/rc80211_minstrel.h    |  6 ++++--
 net/mac80211/rc80211_minstrel_ht.c |  1 -
 3 files changed, 12 insertions(+), 17 deletions(-)

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index aa59f29..c28e60a 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -55,7 +55,6 @@
 #include "rate.h"
 #include "rc80211_minstrel.h"
 
-#define SAMPLE_COLUMNS	10
 #define SAMPLE_TBL(_mi, _idx, _col) \
 		_mi->sample_table[(_idx * SAMPLE_COLUMNS) + _col]
 
@@ -210,7 +209,7 @@ minstrel_get_next_sample(struct minstrel_sta_info *mi)
 	unsigned int sample_ndx;
 	sample_ndx = SAMPLE_TBL(mi, mi->sample_row, mi->sample_column);
 	mi->sample_row++;
-	if ((int) mi->sample_row > (mi->n_rates - 2)) {
+	if ((int) mi->sample_row >= mi->n_rates) {
 		mi->sample_row = 0;
 		mi->sample_column++;
 		if (mi->sample_column >= SAMPLE_COLUMNS)
@@ -370,26 +369,21 @@ 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];
+	u8 rnd[mi->n_rates];
 
 	mi->sample_column = 0;
 	mi->sample_row = 0;
-	memset(mi->sample_table, 0, SAMPLE_COLUMNS * mi->n_rates);
+	memset(mi->sample_table, 0xff, SAMPLE_COLUMNS * mi->n_rates);
 
 	for (col = 0; col < SAMPLE_COLUMNS; col++) {
-		for (i = 0; i < n_srates; i++) {
+		for (i = 0; i < mi->n_rates; i++) {
 			get_random_bytes(rnd, sizeof(rnd));
-			new_idx = (i + rnd[i & 7]) % n_srates;
+			new_idx = (i + rnd[i]) % mi->n_rates;
 
-			while (SAMPLE_TBL(mi, new_idx, col) != 0)
-				new_idx = (new_idx + 1) % n_srates;
+			while (SAMPLE_TBL(mi, new_idx, col) != 0xff)
+				new_idx = (new_idx + 1) % mi->n_rates;
 
-			/* 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;
+			SAMPLE_TBL(mi, new_idx, col) = i;
 		}
 	}
 }
diff --git a/net/mac80211/rc80211_minstrel.h b/net/mac80211/rc80211_minstrel.h
index 200b7e3..49a770b 100644
--- a/net/mac80211/rc80211_minstrel.h
+++ b/net/mac80211/rc80211_minstrel.h
@@ -9,7 +9,9 @@
 #ifndef __RC_MINSTREL_H
 #define __RC_MINSTREL_H
 
-#define EWMA_LEVEL 75	/* ewma weighting factor [%] */
+#define EWMA_LEVEL	75	/* ewma weighting factor [%] */
+#define SAMPLE_COLUMNS	10	/* number of columns in sample table */
+
 
 /* scaled fraction values */
 #define MINSTREL_SCALE  16
@@ -78,7 +80,7 @@ struct minstrel_sta_info {
 	bool prev_sample;
 
 	/* sampling table */
-	u8 *sample_table;
+	void *sample_table;
 
 #ifdef CONFIG_MAC80211_DEBUGFS
 	struct dentry *dbg_stats;
diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
index a3081e5..8f88108 100644
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -17,7 +17,6 @@
 #include "rc80211_minstrel_ht.h"
 
 #define AVG_PKT_SIZE	1200
-#define SAMPLE_COLUMNS	10
 
 /* Number of bits for an average sized packet */
 #define MCS_NBITS (AVG_PKT_SIZE << 3)
-- 
1.8.1.1

[PATCH 6/7] mac80211: treat minstrel success probabilities below 10% as implausible

[Thomas Huehn]

Based on minstrel_ht this patch treats success probabilities below 10% as
implausible values for throughput calculation in minstrel's statistics.
Current throughput per rate with such a low success probability is reset
to 0 MBit/s.

Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
---
 net/mac80211/rc80211_minstrel.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index c28e60a..8af71f6 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -92,7 +92,6 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 			mr->probability = minstrel_ewma(mr->probability,
 							mr->cur_prob,
 							EWMA_LEVEL);
-			mr->cur_tp = mr->probability * (1000000 / usecs);
 		} else
 			mr->sample_skipped++;
 
@@ -101,6 +100,12 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 		mr->success = 0;
 		mr->attempts = 0;
 
+		/* Update throughput per rate, reset thr. below 10% success */
+		if (mr->probability < MINSTREL_FRAC(10, 100))
+			mr->cur_tp = 0;
+		else
+			mr->cur_tp = mr->probability * (1000000 / usecs);
+
 		/* Sample less often below the 10% chance of success.
 		 * Sample less often above the 95% chance of success. */
 		if (mr->probability > MINSTREL_FRAC(95, 100) ||
-- 
1.8.1.1

[PATCH 7/7] mac80211: improve minstrels rate sorting by means of throughput & probability

[Thomas Huehn]

This patch improves the way minstrel sorts rates according to throughput
and success probability. 3 FOR-loops across the entire rate set in function
minstrel_update_stats() which where used to determine the fastest, second
fastest and most robust rate are reduced to 1 FOR-loop.

The sorted list of rates according throughput is extended to the best four
rates as we need them in upcoming joint rate and power control.

The most robust rate selection is aligned with minstrel_ht's approach.
Once any success probability is above 95% the one with the highest
throughput is chosen as most robust rate. If success probabilities of all
rates are below 95%, the rate with the highest succ. prob. is elected as
most robust one

Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
---
 net/mac80211/rc80211_minstrel.c         | 66 +++++++++++++++++----------------
 net/mac80211/rc80211_minstrel.h         | 10 +++--
 net/mac80211/rc80211_minstrel_debugfs.c |  6 ++-
 3 files changed, 45 insertions(+), 37 deletions(-)

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index 8af71f6..221b5f4 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -72,13 +72,17 @@ rix_to_ndx(struct minstrel_sta_info *mi, int rix)
 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;
+	u8 tmp_tp_rate[MAX_THR_RATES];
+	u8 tmp_prob_rate = 0;
 	u32 usecs;
 	int i;
 
+	for (i=0; i < MAX_THR_RATES; i++)
+	    tmp_tp_rate[i] = 0;
+
 	for (i = 0; i < mi->n_rates; i++) {
 		struct minstrel_rate *mr = &mi->r[i];
+		int j = MAX_THR_RATES;
 
 		usecs = mr->perfect_tx_time;
 		if (!usecs)
@@ -120,35 +124,35 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 		}
 		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;
+		/* Find 1st, 2nd, 3rd & 4th best throughput rate */
+		//printk(KERN_ERR "before sort: max_tp_rate[0]= %i, [1]= %i, [2]= %i, [3]= %i,", mi->max_tp_rate[0], mi->max_tp_rate[1], mi->max_tp_rate[2], mi->max_tp_rate[3]);
+		while (j > 0 && mr->cur_tp > mi->r[tmp_tp_rate[j - 1]].cur_tp)
+			j--;
+		if (j < MAX_THR_RATES - 1)
+			memmove(&tmp_tp_rate[j + 1], &tmp_tp_rate[j], MAX_THR_RATES - (j + 1));
+		if (j < MAX_THR_RATES)
+			tmp_tp_rate[j] = i;
+		//printk(KERN_ERR "after sort with j=%i : max_tp_rate[0]= %i, [1]= %i, [2]= %i, [3]= %i,", j, mi->max_tp_rate[0], mi->max_tp_rate[1], mi->max_tp_rate[2], mi->max_tp_rate[3]);
+
+		/* To determine the most robust rate (max_prob_rate) used at
+		 * 3rd mmr stage we distinct between two cases:
+		 * (1) if any success probabilitiy >= 95%, out of those rates
+		 * choose the maximum throughput rate as max_prob_rate
+		 * (2) if all success probabilities < 95%, the rate with
+		 * highest success probability is choosen as max_prob_rate */
+		if (mr->probability >= MINSTREL_FRAC(95,100)) {
+			if (mr->cur_tp >= mi->r[tmp_prob_rate].cur_tp)
+				tmp_prob_rate = i;
+		} else {
+			if (mr->probability >= mi->r[tmp_prob_rate].probability)
+				tmp_prob_rate = i;
 		}
 	}
 
-	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;
+	/* Assign the new rate set */
+	memcpy(mi->max_tp_rate, tmp_tp_rate, sizeof(mi->max_tp_rate));
+	mi->max_prob_rate = tmp_prob_rate;
 
 	/* Reset update timer */
 	mi->stats_update = jiffies;
@@ -254,7 +258,7 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
 		sampling_ratio = mp->lookaround_rate;
 
 	/* init rateindex [ndx] with max throughput rate */
-	ndx = mi->max_tp_rate;
+	ndx = mi->max_tp_rate[0];
 
 	/* increase sum packet counter */
 	mi->packet_count++;
@@ -322,7 +326,7 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
 	 * to use it, as this only wastes precious airtime */
 	if (!mrr_capable && rate_sampling &&
 	   (mi->r[ndx].probability > MINSTREL_FRAC(95, 100)))
-		ndx = mi->max_tp_rate;
+		ndx = mi->max_tp_rate[0];
 
 	/* mrr setup for 1st stage */
 	ar[0].idx = mi->r[ndx].rix;
@@ -342,9 +346,9 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
 		if (indirect_rate_sampling)
 			mrr_ndx[0] = sample_ndx;
 		else
-			mrr_ndx[0] = mi->max_tp_rate;
+			mrr_ndx[0] = mi->max_tp_rate[0];
 	} else {
-		mrr_ndx[0] = mi->max_tp_rate2;
+		mrr_ndx[0] = mi->max_tp_rate[1];
 	}
 
 	/* mrr setup for 3rd & 4th stage */
diff --git a/net/mac80211/rc80211_minstrel.h b/net/mac80211/rc80211_minstrel.h
index 49a770b..85ebf42 100644
--- a/net/mac80211/rc80211_minstrel.h
+++ b/net/mac80211/rc80211_minstrel.h
@@ -18,6 +18,9 @@
 #define MINSTREL_FRAC(val, div) (((val) << MINSTREL_SCALE) / div)
 #define MINSTREL_TRUNC(val) ((val) >> MINSTREL_SCALE)
 
+/* number of highest throughput rates to consider*/
+#define MAX_THR_RATES 4
+
 /*
  * Perform EWMA (Exponentially Weighted Moving Average) calculation
   */
@@ -65,9 +68,8 @@ struct minstrel_sta_info {
 
 	unsigned int lowest_rix;
 
-	unsigned int max_tp_rate;
-	unsigned int max_tp_rate2;
-	unsigned int max_prob_rate;
+	u8 max_tp_rate[MAX_THR_RATES];
+	u8 max_prob_rate;
 	unsigned int packet_count;
 	unsigned int sample_count;
 	int sample_deferred;
@@ -80,7 +82,7 @@ struct minstrel_sta_info {
 	bool prev_sample;
 
 	/* sampling table */
-	void *sample_table;
+	u8 *sample_table;
 
 #ifdef CONFIG_MAC80211_DEBUGFS
 	struct dentry *dbg_stats;
diff --git a/net/mac80211/rc80211_minstrel_debugfs.c b/net/mac80211/rc80211_minstrel_debugfs.c
index c0ebfac..d104834 100644
--- a/net/mac80211/rc80211_minstrel_debugfs.c
+++ b/net/mac80211/rc80211_minstrel_debugfs.c
@@ -73,8 +73,10 @@ minstrel_stats_open(struct inode *inode, struct file *file)
 	for (i = 0; i < mi->n_rates; i++) {
 		struct minstrel_rate *mr = &mi->r[i];
 
-		*(p++) = (i == mi->max_tp_rate) ? 'T' : ' ';
-		*(p++) = (i == mi->max_tp_rate2) ? 't' : ' ';
+		*(p++) = (i == mi->max_tp_rate[0]) ? 'A' : ' ';
+		*(p++) = (i == mi->max_tp_rate[1]) ? 'B' : ' ';
+		*(p++) = (i == mi->max_tp_rate[2]) ? 'C' : ' ';
+		*(p++) = (i == mi->max_tp_rate[3]) ? 'D' : ' ';
 		*(p++) = (i == mi->max_prob_rate) ? 'P' : ' ';
 		p += sprintf(p, "%3u%s", mr->bitrate / 2,
 				(mr->bitrate & 1 ? ".5" : "  "));
-- 
1.8.1.1

Re: [PATCH 7/7] mac80211: improve minstrels rate sorting by means of throughput & probability

[Bob Copeland]

On Fri, Mar 01, 2013 at 06:37:36PM +0100, Thomas Huehn wrote:
> +		//printk(KERN_ERR "before sort: max_tp_rate[0]= %i, [1]= %i, [2]= %i, [3]= %i,", mi->max_tp_rate[0], mi->max_tp_rate[1], mi->max_tp_rate[2], mi->max_tp_rate[3]);

Some leftover debugging there, and elsewhere.

I take it the changes to minstrel_update_stats fix the problem where
a rate might get used more than once?  A while ago I wrote the following
patch for that, but never found the time to test it.  It would be great
to know it's fixed.

From: Bob Copeland <me@bobcopeland.com>
Date: Fri, 18 May 2012 22:57:49 -0400
Subject: [PATCH] minstrel: avoid reusing max tp/max prob rates if they are the same

Some testing I did a while ago with mac80211_hwsim showed that
the MRR chain would frequently have the same rate included more
than once because it would be both the "max throughput" rate and
the "max success probability" rate.

If we truly cannot deliver packets with that rate due to changes
in radio conditions, we can waste a lot of airtime with unsuccessful
retransmissions.  So, compute both of the max throughput rates up
front, and then pick the max prob. rate from the leftovers.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
---
 net/mac80211/rc80211_minstrel.c |   21 +++++++++++----------
 1 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index 79633ae..36255f1 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -73,7 +73,7 @@ rix_to_ndx(struct minstrel_sta_info *mi, int rix)
 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_tp = 0, index_max_tp = 0, max_tp2 = 0, index_max_tp2 = 0;
 	u32 max_prob = 0, index_max_prob = 0;
 	u32 usecs;
 	u32 p;
@@ -123,25 +123,26 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 	for (i = 0; i < mi->n_rates; i++) {
 		struct minstrel_rate *mr = &mi->r[i];
 		if (max_tp < mr->cur_tp) {
+			max_tp2 = max_tp;
+			index_max_tp2 = index_max_tp;
 			index_max_tp = i;
 			max_tp = mr->cur_tp;
-		}
-		if (max_prob < mr->probability) {
-			index_max_prob = i;
-			max_prob = mr->probability;
+		} else if (max_tp2 < mr->cur_tp) {
+			index_max_tp2 = i;
+			max_tp2 = mr->cur_tp;
 		}
 	}
 
-	max_tp = 0;
+	max_prob = 0;
 	for (i = 0; i < mi->n_rates; i++) {
 		struct minstrel_rate *mr = &mi->r[i];
 
-		if (i == index_max_tp)
+		if (i == index_max_tp || i == index_max_tp2)
 			continue;
 
-		if (max_tp < mr->cur_tp) {
-			index_max_tp2 = i;
-			max_tp = mr->cur_tp;
+		if (max_prob < mr->probability) {
+			index_max_prob = i;
+			max_prob = mr->probability;
 		}
 	}
 	mi->max_tp_rate = index_max_tp;
-- 
1.7.2.5

-- 
Bob Copeland %% www.bobcopeland.com

Re: [PATCH 0/7] mac80211: improve and consolidate minstrel rate control

[Johannes Berg]

On Fri, 2013-03-01 at 18:37 +0100, Thomas Huehn wrote:
> This patch series merges functions, macros and sampling improvements from
> minstrel_ht into minstrel. It adds several improvements to the rate control.  

Generally, please CC me on this address rather than my @intel.com one
(for patches anyway) -- it tends to fit my workflow better and make it
less likely I'll lose a patch :-)

johannes

Re: [PATCH 7/7] mac80211: improve minstrels rate sorting by means of throughput & probability

[Thomas Hühn]

Hi Bob,


On 01.03.2013, at 19:41, Bob Copeland <me@bobcopeland.com> wrote:

> On Fri, Mar 01, 2013 at 06:37:36PM +0100, Thomas Huehn wrote:
>> +		//printk(KERN_ERR "before sort: max_tp_rate[0]= %i, [1]= %i, [2]= %i, [3]= %i,", mi->max_tp_rate[0], mi->max_tp_rate[1], mi->max_tp_rate[2], mi->max_tp_rate[3]);
> 
> Some leftover debugging there, and elsewhere.
> 

I should have removed the debugging, thx for finding, I will fix this in v2.

> I take it the changes to minstrel_update_stats fix the problem where
> a rate might get used more than once?  A while ago I wrote the following
> patch for that, but never found the time to test it.  It would be great
> to know it's fixed.

This patch brings minstrel-ht's way of electing the max probability rate to minstrel.
It relaxes the max probability criteria in such a way, that in cases where max probability of rates its above 95%, they are treated as if they have equally high success probability and now just the throughput matters as decision criteria. Lets make a concrete example of a minstrel statistic table snap shot:

Rate | Success		| Throughput
	 |  Prob. [%]	|     [MBit/s]
-----------------------------------------
  6	|	98.5		|	6.0
  9	|	99.9		|	8.7
  12	|	95.3		|	11.2
  18	|	99.8		|	17.3
  24	|	95.3		|	21.6
  36  |	90.0		|	29.4
  48  |	90.2		|	37.6
  54  |	84.3		|	39.3

In case we determine the maximal probability rate just by finding highest success prob. it would give us rate 9. With this patch and the "above 95% success everything is just equally successful" we would choose rate 24 as max. probability rate, as it provides the highest throughout among the rates with success prob. > 95%.
If I understand you right, your idea is to avoid equal rates for max_throughput and max_probability. The patch above would use equal rates for max_thr & max_prob. if the channel conditions allow this, so if they are pretty good. In other cases the max. probability rate can be totally different from max_thr. rate. So I do not 
understand the reasoning behind enforcing different rates for max_tp and max_prob. Minstrel will just apply its rule of max_prob_rate regardless if this rate also provides best or second best or other throughput values. Would you mind to this this patch with your hwsim ?

Greetings Thomas


> From: Bob Copeland <me@bobcopeland.com>
> Date: Fri, 18 May 2012 22:57:49 -0400
> Subject: [PATCH] minstrel: avoid reusing max tp/max prob rates if they are the same
> 
> Some testing I did a while ago with mac80211_hwsim showed that
> the MRR chain would frequently have the same rate included more
> than once because it would be both the "max throughput" rate and
> the "max success probability" rate.
> 
> If we truly cannot deliver packets with that rate due to changes
> in radio conditions, we can waste a lot of airtime with unsuccessful
> retransmissions.  So, compute both of the max throughput rates up
> front, and then pick the max prob. rate from the leftovers.
> 
> Signed-off-by: Bob Copeland <me@bobcopeland.com>
> ---
> net/mac80211/rc80211_minstrel.c |   21 +++++++++++----------
> 1 files changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
> index 79633ae..36255f1 100644
> --- a/net/mac80211/rc80211_minstrel.c
> +++ b/net/mac80211/rc80211_minstrel.c
> @@ -73,7 +73,7 @@ rix_to_ndx(struct minstrel_sta_info *mi, int rix)
> 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_tp = 0, index_max_tp = 0, max_tp2 = 0, index_max_tp2 = 0;
> 	u32 max_prob = 0, index_max_prob = 0;
> 	u32 usecs;
> 	u32 p;
> @@ -123,25 +123,26 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
> 	for (i = 0; i < mi->n_rates; i++) {
> 		struct minstrel_rate *mr = &mi->r[i];
> 		if (max_tp < mr->cur_tp) {
> +			max_tp2 = max_tp;
> +			index_max_tp2 = index_max_tp;
> 			index_max_tp = i;
> 			max_tp = mr->cur_tp;
> -		}
> -		if (max_prob < mr->probability) {
> -			index_max_prob = i;
> -			max_prob = mr->probability;
> +		} else if (max_tp2 < mr->cur_tp) {
> +			index_max_tp2 = i;
> +			max_tp2 = mr->cur_tp;
> 		}
> 	}
> 
> -	max_tp = 0;
> +	max_prob = 0;
> 	for (i = 0; i < mi->n_rates; i++) {
> 		struct minstrel_rate *mr = &mi->r[i];
> 
> -		if (i == index_max_tp)
> +		if (i == index_max_tp || i == index_max_tp2)
> 			continue;
> 
> -		if (max_tp < mr->cur_tp) {
> -			index_max_tp2 = i;
> -			max_tp = mr->cur_tp;
> +		if (max_prob < mr->probability) {
> +			index_max_prob = i;
> +			max_prob = mr->probability;
> 		}
> 	}
> 	mi->max_tp_rate = index_max_tp;
> -- 
> 1.7.2.5
> 
> -- 
> Bob Copeland %% www.bobcopeland.com
> --
> To unsubscribe from this list: send the line "unsubscribe linux-wireless" in
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> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH 7/7] mac80211: improve minstrels rate sorting by means of throughput & probability

[Bob Copeland]

On Sat, Mar 02, 2013 at 12:01:59PM +0100, Thomas Hühn wrote:
> Hi Bob,
> 
> I should have removed the debugging, thx for finding, I will fix this in v2.

Thanks!

> If I understand you right, your idea is to avoid equal rates for
> max_throughput and max_probability. The patch above would use equal
> rates for max_thr & max_prob. if the channel conditions allow this, so
> if they are pretty good. In other cases the max. probability rate can
> be totally different from max_thr. rate. So I do not understand the
> reasoning behind enforcing different rates for max_tp and max_prob.
> Minstrel will just apply its rule of max_prob_rate regardless if this
> rate also provides best or second best or other throughput values.

I guess my reasoning is that if you have an MRR setup like this:

mrr0 rate = 24, count = 8  (max_tp)
mrr1 rate = 18, count = 3  (max_tp2)
mrr2 rate = 24, count = 8  (max_prob)
mrr3 rate = 6,  count = 3

...and you are located right next to the microwave that just got
turned on :) ... then that second set of 24 mbit retries may well be
quite some time of wasted airtime vs perhaps picking 12 mbit if the
probability of those rates is close.

[this was an actual table generated by minstrel from my simulation,
at least at the time, max retries was ignored by minstrel.]

> Would you mind to this this patch with your hwsim ?

That is a bit complicated :)  To do so requires porting my userspace
wifi simulator to wmediumd, a process I have started but haven't
put much time into.  Nevertheless it has been on my personal to-do for
quite some time, so I'll give it a go soon.  I wouldn't hold up
acceptance of the patches for my testing though.

-- 
Bob Copeland %% www.bobcopeland.com