mac80211: fix contention time computation in minstrel, minstrel_ht
When transmitting a frame, the transmitter waits a random number of
slots between 0 and cw. Thus, the contention time is (cw / 2) * t_slot
which we can represent instead as (cw * t_slot) >> 1. Also fix a few
other accounting bugs around contention time, and add comments.
Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index 778c604..8adac67 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -417,8 +417,8 @@
tx_time_single = mr->ack_time + mr->perfect_tx_time;
/* contention window */
- tx_time_single += t_slot + min(cw, mp->cw_max);
- cw = (cw << 1) | 1;
+ tx_time_single += (t_slot * cw) >> 1;
+ cw = min((cw << 1) | 1, mp->cw_max);
tx_time += tx_time_single;
tx_time_cts += tx_time_single + mi->sp_ack_dur;