From: Timo Lindhorst <tlnd@online.de>
To: Johannes Berg <johannes@sipsolutions.net>
Subject: Re: [PATCH] mac80211_hwsim: Report rate info in tx status
Date: Wed, 28 Mar 2012 15:47:21 +0200
Cc: "John W. Linville" <linville@tuxdriver.com>,
	linux-wireless@vger.kernel.org, Jouni Malinen <j@w1.fi>
References: <201203281117.53033.tlnd@online.de> <201203281128.27956.tlnd@online.de> <1332927150.3479.25.camel@jlt3.sipsolutions.net>
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> > > +     if (!ack)
> > > +             for (i = 0; i < IEEE80211_TX_MAX_RATES; i++)
> > > +                     tx_count[i] = txi->control.rates[i].count;
> > > +
> > > 
> > >       ieee80211_tx_info_clear_status(txi);
> > >       if (!(txi->flags & IEEE80211_TX_CTL_NO_ACK) && ack)
> > >       
> > >               txi->flags |= IEEE80211_TX_STAT_ACK;
> > > 
> > > +
> > > +     if (ack) {
> > > +             txi->status.rates[0].count = 1;
> > > +             txi->status.rates[1].idx = -1;
> > > +     } else {
> > > +             for (i = 0; i < IEEE80211_TX_MAX_RATES; i++)
> > > +                     txi->control.rates[i].count = tx_count[i];
> > > +     }
> > > +
> > > 
> > >       ieee80211_tx_status_irqsafe(hw, skb);
> > >  
> > >  }
> > 
> > I know: backing up the count values, clearing the status, and restoring
> > the values if necessary is kind of ugly. Would it be better to partly
> > clear the status manually instead of using
> > ieee80211_tx_info_clear_status() ?
> 
> Yeah just noticed the ieee80211_tx_info_clear_status() in there too...
> 
> OTOH, what are you using this for?
While working on some modifications to the rate control code, I thought it 
would be handy to use mac80211_hwsim for debugging and testing. Thereby I 
noticed that the tx status does not report any tx attempts, thus the rate 
control could not work at all.

> It seems almost like we should always
> just set
> 	txi->status.rates[0].count = 1;

At least,
	txi->status.rates[1].idx = -1;
has to be set too, to indicate that only the first rate was used.


> since we never attempted multiple transmits? I'm not really sure though,
> it's a corner case ... 
We would only attempt multiple transmits if the receiver is not responding to 
unicast frames -- maybe because it has failed or switched the channel. 
Probably not a common use case, but that was what I was testing...


> I could also imagine this being populated by
> userspace (wmediumd) but I guess that isn't there now ...
Right, but if you are not using wmediumd but the bare mac80211_hwsim ideal 
channel, there would be no rate information and thus no rate adaption through 
the rate control algorithm.

Regards
Timo