Re: [PATCH v2 net-next] net: dsa: felix: enable cut-through forwarding between ports by default

On Thu, Nov 25, 2021 at 07:29:09AM -0800, Jakub Kicinski wrote:

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Obviously shooting from the hip here, but I was expecting the cut-thru
update to be before the bridge reconfig if port is joining, and after
if port is leaving. Do you know what I'm getting at?  

Yes, I know what you're getting at. But it's a bit complicated to do,
given the layering constraints and that cut-through forwarding is an
optional feature which isn't present on all devices, so I am trying to
keep its footprint minimal on the ocelot library.

What I can do is I can disable cut-through forwarding for ports that are
standalone (not in a bridge). I don't have a use case for that anyway:
the store-and-forward latency is indistinguishable from network stack
latency. This will guarantee that when a port joins a bridge, it has
cut-through forwarding disabled. So there are no issues if it happens to
join a bridge and its link speed is higher than anybody else: there will
be no packet underruns.

Hm, to make sure I understand - fixing standalone ports doesn't
necessary address the issue of a slow standalone port joining, right?

Yeah, I think I handled it better in v3 than my initial idea here.