At high data rates the average frame transmission durations are small
enough for rounding errors to matter, sometimes causing minstrel to use
slightly lower transmit rates than necessary.
To fix this, change the unit of the duration value to nanoseconds
instead of microseconds, and reorder the multiplications/divisions when
calculating the throughput metric so that they don't overflow or
truncate prematurely.
At 2-stream HT40 this makes TCP throughput a bit more stable.
Signed-off-by: Felix Fietkau <[email protected]>
---
net/mac80211/rc80211_minstrel_ht.c | 23 +++++++++++++----------
1 file changed, 13 insertions(+), 10 deletions(-)
diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
index 3af141c..0b5cdd9 100644
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -26,11 +26,11 @@
/* Number of symbols for a packet with (bps) bits per symbol */
#define MCS_NSYMS(bps) ((MCS_NBITS + (bps) - 1) / (bps))
-/* Transmission time for a packet containing (syms) symbols */
+/* Transmission time (nanoseconds) for a packet containing (syms) symbols */
#define MCS_SYMBOL_TIME(sgi, syms) \
(sgi ? \
- ((syms) * 18 + 4) / 5 : /* syms * 3.6 us */ \
- (syms) << 2 /* syms * 4 us */ \
+ ((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 */
@@ -64,9 +64,9 @@
}
#define CCK_DURATION(_bitrate, _short, _len) \
- (10 /* SIFS */ + \
+ (1000 * (10 /* SIFS */ + \
(_short ? 72 + 24 : 144 + 48 ) + \
- (8 * (_len + 4) * 10) / (_bitrate))
+ (8 * (_len + 4) * 10) / (_bitrate)))
#define CCK_ACK_DURATION(_bitrate, _short) \
(CCK_DURATION((_bitrate > 10 ? 20 : 10), false, 60) + \
@@ -211,7 +211,8 @@ static void
minstrel_ht_calc_tp(struct minstrel_ht_sta *mi, int group, int rate)
{
struct minstrel_rate_stats *mr;
- unsigned int usecs = 0;
+ unsigned int nsecs = 0;
+ unsigned int tp;
mr = &mi->groups[group].rates[rate];
@@ -221,10 +222,12 @@ minstrel_ht_calc_tp(struct minstrel_ht_sta *mi, int group, int rate)
}
if (group != MINSTREL_CCK_GROUP)
- usecs = mi->overhead / MINSTREL_TRUNC(mi->avg_ampdu_len);
+ nsecs = 1000 * mi->overhead / MINSTREL_TRUNC(mi->avg_ampdu_len);
- usecs += minstrel_mcs_groups[group].duration[rate];
- mr->cur_tp = MINSTREL_TRUNC((1000000 / usecs) * mr->probability);
+ nsecs += minstrel_mcs_groups[group].duration[rate];
+ tp = 1000000 * ((mr->probability * 1000) / nsecs);
+
+ mr->cur_tp = MINSTREL_TRUNC(tp);
}
/*
@@ -536,7 +539,7 @@ minstrel_calc_retransmit(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
mr->retry_updated = true;
group = &minstrel_mcs_groups[index / MCS_GROUP_RATES];
- tx_time_data = group->duration[index % MCS_GROUP_RATES] * ampdu_len;
+ tx_time_data = group->duration[index % MCS_GROUP_RATES] * ampdu_len / 1000;
/* Contention time for first 2 tries */
ctime = (t_slot * cw) >> 1;
--
1.8.0.2
On Sat, 2013-03-02 at 21:20 +0100, Felix Fietkau wrote:
> At high data rates the average frame transmission durations are small
> enough for rounding errors to matter, sometimes causing minstrel to use
> slightly lower transmit rates than necessary.
> To fix this, change the unit of the duration value to nanoseconds
> instead of microseconds, and reorder the multiplications/divisions when
> calculating the throughput metric so that they don't overflow or
> truncate prematurely.
> At 2-stream HT40 this makes TCP throughput a bit more stable.
Applied all 3.
johannes
max_prob_rate should be selected to be very reliable, however limiting
it to single-stream on 3-stream devices is a bit much.
Allow max_prob_rate to use one stream less than the max_tp_rate.
Signed-off-by: Felix Fietkau <[email protected]>
---
net/mac80211/rc80211_minstrel_ht.c | 27 +++++++++++++++++++--------
1 file changed, 19 insertions(+), 8 deletions(-)
diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
index 0b5cdd9..6c735e0 100644
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -246,6 +246,7 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
struct minstrel_rate_stats *mr;
int cur_prob, cur_prob_tp, cur_tp, cur_tp2;
int group, i, index;
+ int prob_max_streams = 1;
if (mi->ampdu_packets > 0) {
mi->avg_ampdu_len = minstrel_ewma(mi->avg_ampdu_len,
@@ -323,20 +324,13 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
if (!mg->supported)
continue;
- mr = minstrel_get_ratestats(mi, mg->max_prob_rate);
- if (cur_prob_tp < mr->cur_tp &&
- minstrel_mcs_groups[group].streams == 1) {
- mi->max_prob_rate = mg->max_prob_rate;
- cur_prob = mr->cur_prob;
- cur_prob_tp = mr->cur_tp;
- }
-
mr = minstrel_get_ratestats(mi, mg->max_tp_rate);
if (cur_tp < mr->cur_tp) {
mi->max_tp_rate2 = mi->max_tp_rate;
cur_tp2 = cur_tp;
mi->max_tp_rate = mg->max_tp_rate;
cur_tp = mr->cur_tp;
+ prob_max_streams = minstrel_mcs_groups[group].streams - 1;
}
mr = minstrel_get_ratestats(mi, mg->max_tp_rate2);
@@ -346,6 +340,23 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
}
}
+ if (prob_max_streams < 1)
+ prob_max_streams = 1;
+
+ for (group = 0; group < ARRAY_SIZE(minstrel_mcs_groups); group++) {
+ mg = &mi->groups[group];
+ if (!mg->supported)
+ continue;
+ mr = minstrel_get_ratestats(mi, mg->max_prob_rate);
+ if (cur_prob_tp < mr->cur_tp &&
+ minstrel_mcs_groups[group].streams <= prob_max_streams) {
+ mi->max_prob_rate = mg->max_prob_rate;
+ cur_prob = mr->cur_prob;
+ cur_prob_tp = mr->cur_tp;
+ }
+ }
+
+
mi->stats_update = jiffies;
}
--
1.8.0.2
Try to sample all available rates, as sample attempts do not cost much
airtime and are appropriately spaced based on the average A-MPDU length.
This helps with faster recovery on rate fluctuations.
Signed-off-by: Felix Fietkau <[email protected]>
---
net/mac80211/rc80211_minstrel_ht.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
index 6c735e0..4d35bc5 100644
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -312,8 +312,8 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
}
}
- /* try to sample up to half of the available rates during each interval */
- mi->sample_count *= 4;
+ /* try to sample all available rates during each interval */
+ mi->sample_count *= 8;
cur_prob = 0;
cur_prob_tp = 0;
--
1.8.0.2