Re: [Cerowrt-devel] archer c7 v2, policing, hostapd, test openwrt build

[Jonathan Morton <chromatix99@gmail.com>]

> On 29 Mar, 2015, at 14:16, Sebastian Moeller <moeller0@gmx.de> wrote:

Okay, so it looks like you get another 5% without any shaping running.  So in summary:

- With no shaping at all, the router is still about 10% down compared to downstream line rate.
- Upstream is fine *if* unidirectional.  The load of servicing downstream traffic hurts upstream badly.
- Turning on HTB + fq_codel loses you 5%.
- Using ingress filtering via IFB loses you another 5%.
- Mangling the Diffserv field loses you yet another 5%.

Those 5% penalties add up.  People might grudgingly accept a 10% loss of bandwidth to be sure of lower latency, and faster hardware would do better than that, but losing 25% is a bit much.

I should be able to run similar tests through my Pentium-MMX within a couple of days, so we can see whether I get similar overhead numbers out of that; I can even try plugging in your shaping settings, since they’re (just) within the line rate of the 100baseTX cards installed in it.  I could also compare cake’s throughput to that of HTB + fq_codel; I’ve already seen an improvement with older versions of cake, but I want to see what the newest version gets too.

Come to think of it, I should probably try swapping the same cards into a faster machine as well, to see how much they influence the result.

>> You see, if we were to use a policer instead of ingress shaping, we’d not only be getting IFB and ingress Diffserv mangling out of the way, but HTB as well.
> 
> But we still would run HTB for egress I assume, and the current results with policers Dave hinted at do not seem like good candidates for replacing shaping…

The point of this exercise was to find out whether a theoretical, ideal policer on ingress might - in theory, mind - give a noticeable improvement of efficiency and thus throughput.

The existing policers available are indeed pretty unsuitable, as Dave’s tests proved, but there may be a way to do better by adapting AQM techniques to the role.  In particular, Codel’s approach of gradually increasing a sparse drop rate seems like it would work better than the “brick wall” imposed by a plain token bucket.

Your results suggest that investigating this possibility might still be worthwhile.  Whether anything will come of it, I don’t know.

 - Jonathan Morton