Subject: Re: [RFC v1] mac80211: minstrel_ht: respect RTS threshold setting

From: Peter Seiderer <[email-masked]>
Date: Tue, 16 Nov 2021 22:10:41 +0100

On Tue, 26 Oct 2021 22:41:44 +0200, Peter Seiderer <[email-masked]> wrote:

> Despite the 'RTS thr:off' setting a wireshark trace of IBSS
> traffic with HT40 mode enabled between two ath9k cards revealed
> some RTS/CTS traffic.
>
> Debug and code analysis showed that most places setting
> IEEE80211_TX_RC_USE_RTS_CTS respect the RTS strategy by
> evaluating rts_threshold, e.g. net/mac80211/tx.c:
>
>  698         /* set up RTS protection if desired */
>  699         if (len > tx->local->hw.wiphy->rts_threshold) {
>  700                 txrc.rts = true;
>  701         }
>  702
>  703         info->control.use_rts = txrc.rts;
>
> or drivers/net/wireless/ath/ath9k/xmit.c
>
> 1238                 /*
> 1239                  * Handle RTS threshold for unaggregated HT frames.
> 1240                  */
> 1241                 if (bf_isampdu(bf) && !bf_isaggr(bf) &&
> 1242                     (rates[i].flags & IEEE80211_TX_RC_MCS) &&
> 1243                     unlikely(rts_thresh != (u32) -1)) {
> 1244                         if (!rts_thresh || (len > rts_thresh))
> 1245                                 rts = true;
> 1246                 }
>
> The only place setting IEEE80211_TX_RC_USE_RTS_CTS unconditionally
> was found in net/mac80211/rc80211_minstrel_ht.c.
>
> Fix this by propagating the calculated use_rts value to the
> minstrel_ht_set_rate() function and evaluate it accordingly
> before setting IEEE80211_TX_RC_USE_RTS_CTS.

Despite my believe after code review the use_rts value is only calculated
after hitting the minstrel_ht code, so my preferred alternative solution
would be to NOT requesting RTS/CTS from the minstrel_ht code (for the
fallback rates case)...., updated patch will follow...

Regards,
Peter

>
> Signed-off-by: Peter Seiderer <[email-masked]>
> ---
>  net/mac80211/rc80211_minstrel_ht.c | 21 ++++++++++++---------
>  1 file changed, 12 insertions(+), 9 deletions(-)
>
> diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
> index 72b44d4c42d0..f52edef443fa 100644
> --- a/net/mac80211/rc80211_minstrel_ht.c
> +++ b/net/mac80211/rc80211_minstrel_ht.c
> @@ -276,7 +276,8 @@ static const u8 minstrel_sample_seq[] = {
>  };
>
>  static void
> -minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi);
> +minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
> +			 bool use_rts);
>
>  /*
>   * Some VHT MCSes are invalid (when Ndbps / Nes is not an integer)
> @@ -1254,7 +1255,7 @@ minstrel_ht_tx_status(void *priv, struct ieee80211_supported_band *sband,
>  	}
>
>  	if (update)
> -		minstrel_ht_update_rates(mp, mi);
> +		minstrel_ht_update_rates(mp, mi, info->control.use_rts);
>  }
>
>  static void
> @@ -1319,7 +1320,8 @@ minstrel_calc_retransmit(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
>
>  static void
>  minstrel_ht_set_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
> -                     struct ieee80211_sta_rates *ratetbl, int offset, int index)
> +		     struct ieee80211_sta_rates *ratetbl, int offset, int index,
> +		     bool use_rts)
>  {
>  	int group_idx = MI_RATE_GROUP(index);
>  	const struct mcs_group *group = &minstrel_mcs_groups[group_idx];
> @@ -1357,7 +1359,7 @@ minstrel_ht_set_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
>  	 *  - if station is in dynamic SMPS (and streams > 1)
>  	 *  - for fallback rates, to increase chances of getting through
>  	 */
> -	if (offset > 0 ||
> +	if ((offset > 0 && use_rts) ||
>  	    (mi->sta->smps_mode == IEEE80211_SMPS_DYNAMIC &&
>  	     group->streams > 1)) {
>  		ratetbl->rate[offset].count = ratetbl->rate[offset].count_rts;
> @@ -1426,7 +1428,8 @@ minstrel_ht_get_max_amsdu_len(struct minstrel_ht_sta *mi)
>  }
>
>  static void
> -minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
> +minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
> +			 bool use_rts)
>  {
>  	struct ieee80211_sta_rates *rates;
>  	int i = 0;
> @@ -1436,15 +1439,15 @@ minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
>  		return;
>
>  	/* Start with max_tp_rate[0] */
> -	minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_tp_rate[0]);
> +	minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_tp_rate[0], use_rts);
>
>  	if (mp->hw->max_rates >= 3) {
>  		/* At least 3 tx rates supported, use max_tp_rate[1] next */
> -		minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_tp_rate[1]);
> +		minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_tp_rate[1], use_rts);
>  	}
>
>  	if (mp->hw->max_rates >= 2) {
> -		minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_prob_rate);
> +		minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_prob_rate, use_rts);
>  	}
>
>  	mi->sta->max_rc_amsdu_len = minstrel_ht_get_max_amsdu_len(mi);
> @@ -1705,7 +1708,7 @@ minstrel_ht_update_caps(void *priv, struct ieee80211_supported_band *sband,
>
>  	/* create an initial rate table with the lowest supported rates */
>  	minstrel_ht_update_stats(mp, mi);
> -	minstrel_ht_update_rates(mp, mi);
> +	minstrel_ht_update_rates(mp, mi, false);
>  }
>
>  static void