[PATCH v4] mac80211: minstrel: Change expected throughput unit back to Kbps

[PATCH v4] mac80211: minstrel: Change expected throughput unit back to Kbps

[Sven Eckelmann]

The change from cur_tp to the function
minstrel_get_tp_avg/minstrel_ht_get_tp_avg changed the unit used for the
current throughput. For example in minstrel_ht the correct
conversion between them would be:

    mrs->cur_tp / 10 == minstrel_ht_get_tp_avg(..).

This factor 10 must also be included in the calculation of
minstrel_get_expected_throughput and minstrel_ht_get_expected_throughput to
return values with the unit [Kbps] instead of [10Kbps]. Otherwise routing
algorithms like B.A.T.M.A.N. V will make incorrect decision based on these
values. Its kernel based implementation expects expected_throughput always
to have the unit [Kbps] and not sometimes [10Kbps] and sometimes [Kbps].

The same requirement has iw or olsrdv2's nl80211 based statistics module
which retrieve the same data via NL80211_STA_INFO_TX_BITRATE.

Fixes: 6a27b2c40b48 ("mac80211: restructure per-rate throughput calculation into function")
Signed-off-by: Sven Eckelmann <sven@open-mesh.com>
---
v4:
- unify way how multiplication/division is done in
  minstrel_get_expected_throughput and minstrel_ht_get_expected_throughput
v3:
- fix typo in title
- extend description to better explain why this is important
v2:
- Modified PATCH title
---
 net/mac80211/rc80211_minstrel.c    | 2 +-
 net/mac80211/rc80211_minstrel_ht.c | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index 3ece7d1..b54f398 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -711,7 +711,7 @@ static u32 minstrel_get_expected_throughput(void *priv_sta)
 	 * computing cur_tp
 	 */
 	tmp_mrs = &mi->r[idx].stats;
-	tmp_cur_tp = minstrel_get_tp_avg(&mi->r[idx], tmp_mrs->prob_ewma);
+	tmp_cur_tp = minstrel_get_tp_avg(&mi->r[idx], tmp_mrs->prob_ewma) * 10;
 	tmp_cur_tp = tmp_cur_tp * 1200 * 8 / 1024;
 
 	return tmp_cur_tp;
diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
index 3928dbd..f3e9ba4 100644
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -1334,7 +1334,8 @@ static u32 minstrel_ht_get_expected_throughput(void *priv_sta)
 	prob = mi->groups[i].rates[j].prob_ewma;
 
 	/* convert tp_avg from pkt per second in kbps */
-	tp_avg = minstrel_ht_get_tp_avg(mi, i, j, prob) * AVG_PKT_SIZE * 8 / 1024;
+	tp_avg = minstrel_ht_get_tp_avg(mi, i, j, prob) * 10;
+	tp_avg = tp_avg * AVG_PKT_SIZE * 8 / 1024;
 
 	return tp_avg;
 }
-- 
2.7.0

Re: [PATCH v4] mac80211: minstrel: Change expected throughput unit back to Kbps

[Johannes Berg]

On Tue, 2016-02-02 at 08:12 +0100, Sven Eckelmann wrote:
> The change from cur_tp to the function
> minstrel_get_tp_avg/minstrel_ht_get_tp_avg changed the unit used for
> the
> current throughput. For example in minstrel_ht the correct
> conversion between them would be:
> 
>     mrs->cur_tp / 10 == minstrel_ht_get_tp_avg(..).
> 
> This factor 10 must also be included in the calculation of
> minstrel_get_expected_throughput and
> minstrel_ht_get_expected_throughput to
> return values with the unit [Kbps] instead of [10Kbps]. Otherwise
> routing
> algorithms like B.A.T.M.A.N. V will make incorrect decision based on
> these
> values. Its kernel based implementation expects expected_throughput
> always
> to have the unit [Kbps] and not sometimes [10Kbps] and sometimes
> [Kbps].
> 
Applied; also added Cc stable.

johannes