netdev - Re: [PATCH RFC net-next 0/3] Multi-CPU DSA support

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Date:   Tue, 13 Apr 2021 01:54:50 +0200
From:   Marek Behun <marek.behun@....cz>
To:     Tobias Waldekranz <tobias@...dekranz.com>
Cc:     Vladimir Oltean <olteanv@...il.com>,
        Ansuel Smith <ansuelsmth@...il.com>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        Eric Dumazet <edumazet@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        Cong Wang <cong.wang@...edance.com>,
        Taehee Yoo <ap420073@...il.com>,
        Björn Töpel <bjorn@...nel.org>,
        zhang kai <zhangkaiheb@....com>,
        Weilong Chen <chenweilong@...wei.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Di Zhu <zhudi21@...wei.com>,
        Francis Laniel <laniel_francis@...vacyrequired.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC net-next 0/3] Multi-CPU DSA support

On Tue, 13 Apr 2021 01:13:53 +0200
Tobias Waldekranz <tobias@...dekranz.com> wrote:

> > ...you could get the isolation in place. But you will still lookup the
> > DA in the ATU, and there you will find a destination of either cpu0 or
> > cpu1. So for one of the ports, the destination will be outside of its
> > port based VLAN. Once the vectors are ANDed together, it is left with no
> > valid port to egress through, and the packet is dropped.
> >  
> >> Am I wrong? I confess that I did not understand this into the most fine
> >> details, so it is entirely possible that I am missing something
> >> important and am completely wrong. Maybe this cannot be done.  
> >
> > I really doubt that it can be done. Not in any robust way at
> > least. Happy to be proven wrong though! :)  
> 
> I think I figured out why it "works" for you. Since the CPU address is
> never added to the ATU, traffic for it is treated as unknown. Thanks to
> that, it flooded and the isolation brings it together. As soon as
> mv88e6xxx starts making use of Vladimirs offloading of host addresses
> though, I suspect this will fall apart.

Hmm :( This is bad news. I would really like to make it balance via
input ports. The LAG balancing for this usecase is simply unacceptable,
since the switch puts so little information into the hash function.

I will look into this, maybe ask some follow-up questions.

Marek