[Make-wifi-fast] Must a WiFi link be fully loaded to get an accurate latency measurement?

[Toke Høiland-Jørgensen]

Tim Higgins <tim at smallnetbuilder.com> writes:

> One of the things I've been wondering about as I work on OFDMA testing is how
> heavily a WiFi link needs to be loaded.
> As far as I can tell, all (most/many) of the flent scripts basically have
> netperf TCP/IP streams running full tilt.
>
> I guess put another way, how effective are the anti-bufferbloat methods at
> reducing latency on a moderately loaded link?

Well, the anti-bufferbloat mitigations aim at managing packet queues.
But if the link is not loaded to capacity, packets will generally be
sent out as soon as they arrive, so there won't *be* any queue to
manage. Which means that as far as queueing is concerned, it doesn't
really matter what you do. There are other factors that can impact the
latency of an idle link, of course, but we haven't really touched those
much when working on the bloat stuff..

> In terms of WiFi, do I need to run a link at 90+ airtime congestion to
> see OFDMA work it's magic? Or would the lack of available airtime
> hinder it working?

Now this is a good question. I would expect that OFDMA to only kick in
if there is actually data queued for multiple stations. I mean,
otherwise it doesn't really gain you much? There is probably also a
tradeoff in how long you hold back packets while waiting for more data
to show up; wait too long and you're just wasting airtime, but if you
don't wait long enough you get no benefit. How the firmware scheduler
manages that is of course vital; but I guess that's what you're trying
to find out? :)

-Toke