A-MSDU reception not working?

Ben Greear greearb at candelatech.com
Mon Jun 30 13:28:24 PDT 2014

On 06/30/2014 01:15 PM, Denton Gentry wrote:
> In iperf tests using a MacBook STA bridging through an ath10k AP to an
> Ethernet server, I'm noticing very selective packet loss. The second
> and subsequent frames in an A-MSDU packet appear to be dropped.
> The AP sets the A-MSDU size to 3839 bytes, and the MacBook frequently
> sends A-MSDU packets containing two TCP frames. So far as I can tell,
> the first TCP frame from an A-MSDU aggregate is delivered and the
> second is consistently lost. The MacBook generally retransmits the
> lost frame as a singleton with no aggregation, and the retransmitted
> frame makes it through.
> This became more noticeable after the reordering fixes in
> http://lists.infradead.org/pipermail/ath10k/2014-June/002552.html
> I see this A-MSDU packet loss behavior both with and without the
> reordering fixes, the first packet in an A-MSDU is delivered while the
> second is dropped. However, *without* the reordering fixes (and
> therefore with packets delivered out of order) the MacBook sends
> relatively few A-MSDU frames. *With* the reordering fixes, so all
> packets are delivered in order, the MacBook keeps sending A-MSDU and
> therefore has to deal with more packet loss. I suspect it is an
> interaction with the MacOS TCP congestion window which I'm likely
> never going to fully understand, its stuck in a region of the
> congestion window where the Wifi driver keeps choosing to using

We saw a case where ath10k AP would drop all UDP PDUs over about 3800 bytes,
I would guess it might be the same problem.

We have not looked into the problem yet.  Stations work fine
(which is our main concern at present)...


Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com

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