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Commit 8fddddff authored by Daniel Halperin's avatar Daniel Halperin Committed by John W. Linville
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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: default avatarDaniel Halperin <dhalperi@cs.washington.edu>
Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
parent 56d1893d

net/mac80211/rc80211_minstrel.c

+2 −2
Original line number Diff line number Diff line
@@ -417,8 +417,8 @@ minstrel_rate_init(void *priv, struct ieee80211_supported_band *sband, 
			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;

net/mac80211/rc80211_minstrel_ht.c

+21 −6
Original line number Diff line number Diff line
@@ -464,6 +464,7 @@ minstrel_calc_retransmit(struct minstrel_priv *mp, struct minstrel_ht_sta *mi, 
	const struct mcs_group *group;

	unsigned int tx_time, tx_time_rtscts, tx_time_data;

	unsigned int cw = mp->cw_min;

	unsigned int ctime = 0;

	unsigned int t_slot = 9; /* FIXME */

	unsigned int ampdu_len = MINSTREL_TRUNC(mi->avg_ampdu_len);
@@ -480,13 +481,27 @@ minstrel_calc_retransmit(struct minstrel_priv *mp, struct minstrel_ht_sta *mi, 


	group = &minstrel_mcs_groups[index / MCS_GROUP_RATES];

	tx_time_data = group->duration[index % MCS_GROUP_RATES] * ampdu_len;

	tx_time = 2 * (t_slot + mi->overhead + tx_time_data);

	tx_time_rtscts = 2 * (t_slot + mi->overhead_rtscts + tx_time_data);



	/* Contention time for first 2 tries */

	ctime = (t_slot * cw) >> 1;

	cw = min((cw << 1) | 1, mp->cw_max);

	ctime += (t_slot * cw) >> 1;

	cw = min((cw << 1) | 1, mp->cw_max);



	/* Total TX time for data and Contention after first 2 tries */

	tx_time = ctime + 2 * (mi->overhead + tx_time_data);

	tx_time_rtscts = ctime + 2 * (mi->overhead_rtscts + tx_time_data);



	/* See how many more tries we can fit inside segment size */

	do {

		cw = (cw << 1) | 1;

		cw = min(cw, mp->cw_max);

		tx_time += cw + t_slot + mi->overhead;

		tx_time_rtscts += cw + t_slot + mi->overhead_rtscts;

		/* Contention time for this try */

		ctime = (t_slot * cw) >> 1;

		cw = min((cw << 1) | 1, mp->cw_max);



		/* Total TX time after this try */

		tx_time += ctime + mi->overhead + tx_time_data;

		tx_time_rtscts += ctime + mi->overhead_rtscts + tx_time_data;



		if (tx_time_rtscts < mp->segment_size)

			mr->retry_count_rtscts++;

	} while ((tx_time < mp->segment_size) &&