Re: Aggregation problem with rt2800 AP and Intel 5100 STA

[Johannes Berg <johannes@sipsolutions.net>]

On Thu, 2011-03-24 at 14:57 +0100, Helmut Schaa wrote:

> I guess so, yes (as I wrote before this is an Intel 5100 client running Windows
> Vista and the latest Intel driver). It sends a nullfunc going to sleep and returns
> a few hundret ms later. And in the meantime I can see my rt2800 AP sending an
> AMPDU to the sleeping STA which of course times out and therefore ends up as
> filtered frame.

Ok so it gets reported to mac80211.

> > Maybe the PS buffer should be larger then?
> 
> 128 frames per STA is already large, no? And also it's nothing unusual
> that some frames get dropped if the STA stays in powersave for a long time.
> 
> > I don't see how we can lose a
> > frame due to rx/tx processing races either, how does that happen? I
> > thought we had the ability to avoid all those races now.
> 
> Good point. Maybe this only happens with rt2x00. The frame exchange looks
> basically like (if you want to see the pcap just ask ;) ):
> 
> STA -> AP  nullfunc PM=1
> AP -> STA  AMPDU (seqnr 3106 - 3112)
> AP -> STA  AMPDU (seqnr 3106 - 3112), retry
> AP -> STA  AMPDU (seqnr 3106 - 3112), retry
> AP -> STA  AMPDU (seqnr 3106 - 3112), retry
> AP -> STA  AMPDU (seqnr 3106 - 3112), retry
> AP -> STA  AMPDU (seqnr 3106 - 3112), retry
> ...
> STA -> AP nullfunc PM=0
> ...
> AP -> STA  AMPDU (seqnr 3108)
> STA -> AP  BlockAck
> AP -> STA  AMPDU (seqnr 3109 - 3114)
> STA -> AP  BlockAck
> ...
> 
> As you can see 3106 and 3107 somehow got lost and thus leave a hole in
> the STAs reorder buffer leading to the strange behavior I described before.

but if they are reported to mac80211 they should be put on the queue
again? Are they maybe not reported back quite in the right way?

> > I don't know, you tell me, does it? :)
> 
> Ha Ha ;)
> 
> Sending a BAR at this point would at least ensure that the Intel STAs RX
> reorder buffer gets flushed (in case we dropped any frames while the STA was
> sleeping, which happened in this case).

Right, but so far this looks like it's more like a bug in the powersave
code rather than something we desperately need to recover from with a
BAR.

johannes