Subject: Re: [PATCH v1 2/2] mac80211: minstrel_ht: fill all requested rates

From: Peter Seiderer <[email-masked]>
Date: Mon, 4 Apr 2022 23:25:12 +0200

Hello Toke, Felix,

On Mon, 04 Apr 2022 20:21:24 +0200, Toke Høiland-Jørgensen <[email-masked]> wrote:

> +Felix
> 
> Peter Seiderer <[email-masked]> writes:
> 
> > Fill all requested rates (in case of ath9k 4 rate slots are
> > available, so fill all 4 instead of only 3), improves throughput in
> > noisy environment.  
> 
> How did you test this? Could you quantify the gains in throughput you saw?

Investigating some performance degradation of a wifi system original with ath5k
cards using a legacy kernel and madwifi driver compared against the 
performance using a ath9k card running IBSS mode over long distance/with
additional amplifier and using iperf for measurement...

With the ath5k cards under bad conditions the throughput is going down below
10 Mbits/s but with stable throughput..., with the ath9k card and the exact same
setup there are short periods with good throughput values and periods up to 10-15
seconds with 0 Mbits/s...

The actual in-door/laboratory test setup is a wired connection between the
two wifi systems (with fixed attenuators in between) and an adjustable noise/
disturb signal induced by a signal generator...

Without this patch the 0 Mbits/s periods from the field test are reproducible,
with this patch applied we see a more or less stable throughput of 1-5 Mbits/s...

Regards,
Peter

> 
> -Toke
> 
> > Signed-off-by: Peter Seiderer <[email-masked]>
> > ---
> >  net/mac80211/rc80211_minstrel_ht.c | 14 +++++++-------
> >  1 file changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
> > index 9c6ace858107..cd6a0f153688 100644
> > --- a/net/mac80211/rc80211_minstrel_ht.c
> > +++ b/net/mac80211/rc80211_minstrel_ht.c
> > @@ -1436,17 +1436,17 @@ minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
> >  	/* Start with max_tp_rate[0] */
> >  	minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_tp_rate[0]);
> >  
> > -	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]);
> > -	}
> > +	/* Fill up remaining, keep one entry for max_probe_rate */
> > +	for (; i < (mp->hw->max_rates - 1); i++)
> > +		minstrel_ht_set_rate(mp, mi, rates, i, mi->max_tp_rate[i]);
> >  
> > -	if (mp->hw->max_rates >= 2) {
> > +	if (i < mp->hw->max_rates)
> >  		minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_prob_rate);
> > -	}
> > +
> > +	if (i < IEEE80211_TX_RATE_TABLE_SIZE)
> > +		rates->rate[i].idx = -1;
> >  
> >  	mi->sta->max_rc_amsdu_len = minstrel_ht_get_max_amsdu_len(mi);
> > -	rates->rate[i].idx = -1;
> >  	rate_control_set_rates(mp->hw, mi->sta, rates);
> >  }
> >  
> > -- 
> > 2.35.1