[Cerowrt-devel] [Make-wifi-fast] wifi airtime fairness patches could use eyeballs and testing

[Toke Høiland-Jørgensen]

Jonathan Morton <chromatix99 at gmail.com> writes:

>> On 11 Aug, 2016, at 01:05, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>> 
>> There are cwnd reductions, yes, but are they drops? My thought was
>> that they were retransmissions caused by OOO packets?
>
> You should be able to find the retransmitted packets, in that case.
> But FQ shouldn’t be reordering packets within the same flow.

No, but the WiFi retransmission logic might. Specifically, the ath9k
will put packets in a retry buffer that takes precedence over new
packets when building aggregates. But since it has one or two aggregates
built already by the time it does this, reordering can occur that way.

Now, digging in to the packet traces (looking at the single flow case,
since that is easier to follow), there's a ~320k segment of the sequence
space that is about 1.5MB and 200 ms late (sequence numbers 10044929
through 10370177 show up after sequence number 11617665 at around the
12k packet mark in the trace). This is nine full aggregates being
reordered.

I'm not really sure the reordering mechanism described above can account
for this, unless there are some pretty serious hardware buffering going
on that we are not aware of. Does anyone else have any ideas?

-Toke