Re: [Make-wifi-fast] the wifi airtime-fair fq_codel stuff on net-next looks mostly good

[Luca Muscariello <luca.muscariello@gmail.com>]

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Air time fairness has a strong theoretical foundation.
So I should cite Newton and say that Toke is sitting on giants' schoulders
:)

In multi rate systems  in a shared channel, time is the right resource to
share.

Then one could discuss about which fairness criterion to use, but that's
secondary.

The criterion used by toke is max-min in time.
I guess this is the best you can do in wifi.
This turns out to be proportional fairness in throughput.

In LTE the shared channel is time shared (slotted)
and fairness is slightly different to max-min in time.

In LTE thanks to the feedback channel, multi user diversity can be used to
schedule transmissions towards the UE with best radio conditions at a given
time.
David Tse showed that this is proportional fairness
with multi user diversity gain. The cell throughout increases
logarithmically with the number of users.
And this is the best criterion for many reasons that I skip here.

This is out of target for wifi but what Toke is doing is really solid.

Luca




On Saturday, 15 October 2016, Mikael Abrahamsson <swmike@swm.pp.se> wrote:

> On Wed, 12 Oct 2016, Dave Taht wrote:
>
> http://openwrtsummit.org/#quick-details
>>
>
> I've had the discussion with "radio guys" before regarding "fairness" of
> radio resources. They kept talking about "optimising the cell for
> throughput". I told them "then we should give the speaker with the highest
> bitrate and demand for bits as much radio resources as possible, and starve
> everybody else". This is of course not good for general customer
> satisfaction.
>
> After a lot of discussions back and forth, we came to the same conclusion
> as you seem to have come to (if I understood Tokes talk correctly), in that
> "radio time" is the most fair resource. If someone has bad radio conditions
> then they get lower total throughput than the one with good radio
> conditions, so the fairness is "equal air time". This means everybody get
> equal part of the shared resource, and gives people an incentive to try to
> improve radio reception if they have trouble, and doesn't starve everybody
> else of airtime just because one device is having a bad radio day.
>
> So full support for this approach from me, good job!
>
> --
> Mikael Abrahamsson    email: swmike@swm.pp.se
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