[Bloat] generic tcp - window scaling limits

[Toke Høiland-Jørgensen]

Matthias Tafelmeier <matthias.tafelmeier at gmx.net> writes:

> Hello,
>
> before bringing it forward to LNX netdev and with the risk of restating
> something, I wanted to hearken for the take of this here, since it's
> also bloating related - when looking at it from the link
> clogging/flowyness point of view.
>
> I first surmised some DQL (as done for driver rings - BQL) introduction
> to the TCP hard limit could improve perceived flow latency - though the
> current hard limit is perfectly enough in conjunction with the window
> advertisement/scaling.
>
> As of what I measured here
>
> https://matthias0tafelmeier.wordpress.com/2017/08/24/linux-tcp-window-scaling-quantification-rmemwmem/

Erm, what exactly are you trying to show here? As far as I can tell from
the last (1-flow) plot, you are saturating the link in all the tests
(and indeed the BDP for a 1Gbps with 2ms RTT is around 250kb), which
means that the TCP flow is limited by cwin and not rwin; so I'm not sure
you are really testing what you say you are.

I'm not sure why the latency varies with the different tests, though;
you sure there's not something else varying? Have you tried running
Flent with the --socket-stats option and taking a look at the actual
window each flow is using?

-Toke