Re: [Make-wifi-fast] [RFC] mac80211: Dynamically set CoDel parameters per station.

[Felix Fietkau <nbd@nbd.name>]

On 2016-09-08 21:59, Toke Høiland-Jørgensen wrote:
> CoDel can be too aggressive if a station sends at a very low rate. This
> gets worse the more stations are present, as each station gets more
> bursty the longer the round-robin scheduling between stations takes.
> 
> This is an attempt to dynamically adjust CoDel parameters per station.
> It takes a rather simple approach and uses a simple binary designation
> of a station as 'slow' if it has expected throughput less than eight
> Mbps (i.e. the lowest couple of rates). In this case, CoDel is set to be
> more lenient by adjusting its target to 50 ms and interval to 300 ms.
> There's a built-in hysteresis so a station cannot flip between slow and
> fast more than once every two seconds.
> 
> In this version the check is performed every time a packet is enqueued
> to the intermediate queues; and the overhead of doing this is alleviated
> a bit by caching the result and by the above-mentioned hysteresis. It
> can probably be smarter about both when and how to do the scaling, but
> this seems to alleviate some of the starvation I've seen with very slow
> stations.
Since this is not dealing properly with firmware rate control anyway,
I'd suggest calling the update from rate_control_set_rates in order to
avoid putting more stuff into the tx hot path.

You could add a separate code path to allow firmware rate control
devices to provide a hint at a convenient point in time.

- Felix