[Bloat] incremental deployment, transport and L4S (Re: when does the CoDel part of fq_codel help in the real world?)

Mikael Abrahamsson swmike at swm.pp.se
Thu Nov 29 03:19:20 EST 2018

On Thu, 29 Nov 2018, Jonathan Morton wrote:

> I'd say the important bits are only slightly harder than doing the same with fq_codel.

Ok, FQ_CODEL is way off to get implemented in HW. I haven't heard anyone 
even discussing it. Have you (or anyone else) heard differently?

> I believe much of Cake's perceived CPU overhead is actually down to 
> inefficiencies in the Linux network stack.  Using a CPU and some modest 
> auxiliary hardware dedicated to moving packets, not tied up in handling 
> general-purpose duties, then achieving greater efficiency with 
> reasonable hardware costs could be quite easy, without losing the 
> flexibility to change algorithms later.

I need to watch the MT7621 packet accelerator talk at the most recent 
OpenWrt summit. I installed OpenWrt 18.06.1 on an Mikrotik RB750vGR3 and 
just clicked my way around in LUCI and enabled flow offload and b00m, it 
now did full gig NAT44 forwarding. It's implemented as a -j FLOWOFFLOAD 
iptables rule. The good thing here might be that we could throw 
unimportant high speed flows off to the accelerator and then just handle 
the time sensitive flows in CPU, and just make sure the CPU has 
preferential access to the media for its time-sensitive flow. That kind of 
approach might make FQ_CODEL deployable even on slow CPU platforms with 
accelerators because you would only run some flows through FQ_CODEL, where 
the bulk high-speed flows would be handed off to acceleration (and we 
guess they don't care about PDV and bufferbloat).

Mikael Abrahamsson    email: swmike at swm.pp.se

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