[c-nsp] Cisco N540-ACC-SYS ipv4 routes

[Saku Ytti]

On Thu, 16 Jul 2020 at 16:31, Tim Durack <tdurack at gmail.com> wrote:

> Not trying to be smart or pedantic: modern routers are built out of lots of "ASICs". I imagine the forwarding element design is the differentiator:

I don't think there is other option here :)

> 1. Fixed pipeline: EARL family
> 2. Progammable pipeline: UADP family
> 3. Run-to-completion: "Silicon One" family
>
> Not an exhaustive list, lots of other examples etc...

I mean what is pipeline? Silicon One is pipeline. Ingress pipe is
parser + npu (terminate) + npu (lookup), egress pipe is npu (rewrite).

Nokia FP is pipeline, but like Silicon one, it's pipeline of identical
NPUs, just lot more identical NPUs in pipeline compared to Silicon
One.

Trio OTOH hits only one core in LU, one given PPE handles everything
for given packet. So not a pipeline.

I like Trio approach more, as the more NPUs you have in the pipeline,
the more difficult it looks to program it right. Because if your NPU1
is parser, and you have big buggy code and your parsing of IPv6
extension headers is pathologically slow, now you're HOLB the whole
line, rest of the cores are doing nothing.
In Trio they don't need to be so careful, as you can think of it as
single fat core in stead of many slim cores in pipe, so you get to use
whole cycle pool, and if not every packet is pathological, you get
away with lot worse ucode design.


-- 
  ++ytti