2016-02-01 22:00:32

by Sven Eckelmann

Subject: [PATCHv3] mac80211: minstrel: Change expected throughput unit back to Kbps

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 <[email protected]>
---
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..8928151 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 *= AVG_PKT_SIZE * 8 / 1024;

return tp_avg;
}
--
2.7.0

2016-02-01 22:53:30

by Johannes Stezenbach

Subject: Re: [PATCHv3] mac80211: minstrel: Change expected throughput unit back to Kbps

Hi Sven,

On Mon, Feb 01, 2016 at 11:00:16PM +0100, Sven Eckelmann wrote:
> - 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 *= AVG_PKT_SIZE * 8 / 1024;

This doesn't look right, in integer arithmetics there is a big
difference between (a * b) / c and a * ( b / c).


Johannes