Subject: Re: bug: iwlwifi, aggregation, and mac80211's reorder buffer
From: Johannes Berg <johannes@sipsolutions.net>
To: Daniel Halperin <dhalperi@cs.washington.edu>
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Date: Tue, 15 Mar 2011 19:52:46 +0100
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On Tue, 2011-03-15 at 11:47 -0700, Daniel Halperin wrote:

> >> [341398.950019] iwlagn 0000:03:00.0: iwlagn_tx_agg_start on ra =
> >> 00:16:ea:c3:b3:8e tid = 0
> >> [341401.790964] New seq exceeds buffering window: 2335, 2304
> >
> > So the delta is always 31, it seems? Is iwlwifi consistently sending
> > batches of 32 instead of the advertised 31?
> 
> I don't think that's the case, in fact I've never seen the hardware
> send a larger batch than frame limit.

Ok.

> I think it's from a missed
> frame early in one batch being pushed out by a late frame in the next
> batch.

Ok, yeah, that'd have the same effect.

>  I know how to get the logs to find out. I have a bunch of
> meetings soon, but I'll dig into this more later.

Thanks.

> > Also -- don't get confused, the tx_agg_start is on its own TX agg
> > session, but the new seq stuff is on its RX agg session.
> 
> You're absolutely true; but both sides pretty much start and stop
> aggregation in sync, they both have the same timeouts and I'm only
> using tcp traffic which is bidirectional.  They're running the same
> software on the same hardware, modulo one being an AP and one a
> client.

Right, if you have bidi traffic like TCP iwlwifi's way of
starting/stopping aggregation will be in sync.

> [Yes, I know that AP mode is broken on the iwl5300 but I disable power
> save, etc., and it seems to work well enough ...  Actually, does AP
> (not P2P) mode work properly on the P2P-supporting 6300?  I could
> switch to using those.]

Yeah, but I wouldn't worry about it in your case right now -- the only
broken thing that I know of is all about powersave.

johannes