[Make-wifi-fast] Thoughts on tackling airtime fairness

David Lang david at lang.hm
Wed May 11 11:24:03 EDT 2016

On Wed, 11 May 2016, Toke Høiland-Jørgensen wrote:

> David Lang <david at lang.hm> writes:
>>> - How to measure the results? Can we dump the information from the
>>>  driver (and is it accurate)? Do we need to parse aircaps? Something
>>>  else?
>> we need to be able to instrament the driver (I don't know if we can
>> get enough data there or not currently)
>> trying to work with aircaps has the problem that what you see in the
>> aircap doesn't match what either the sender or receiver sees
>> Take retransmissions as an example. They only happen because the
>> receiver didn't see them. If you were to get an aircap off the same
>> antenna as the receiver, you also wouldn't see them and therefor could
>> not account for them. In the real world, you are doing the aircap from
>> a different device, with a different antenna so what you see will be
>> even more different. Now think about the normal case where you have
>> two stations taking in two very different locations and one device to
>> do the aircap.
>> If we don't have anything else, aircaps are what we have to fall back
>> on, but we need to realize how much we can't see at that point.
> Hmm, hadn't thought of that. Damn. Well, guess we'll have to trust the
> driver (or make it trustworthy if we can't).

the good news is that getting this information out of the driver should not be 
hard. It knows when it does a retransmit.

I also suspect that we could get away without explictly tracking retransmits for 
now. As it retransmits to a station, it's also going to end up slowing down if 
it's a long-term problem.

we need to think of the scale we are trying to be fair on. I think that if we 
are fair on the scale of seconds we will gain 80% of the effect that we would 
get if we were trying to be fair on the order of ms, and it's much easier to do 

David Lang

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