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

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Message-ID: <20190824152407.GA8251@lunn.ch>
Date:   Sat, 24 Aug 2019 17:24:07 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Marek Behún <marek.behun@....cz>
Cc:     netdev@...r.kernel.org, Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Ahern <dsahern@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH RFC net-next 0/3] Multi-CPU DSA support

On Sat, Aug 24, 2019 at 04:42:47AM +0200, Marek Behún wrote:
> Hi,
> this is my attempt to solve the multi-CPU port issue for DSA.
> 
> Patch 1 adds code for handling multiple CPU ports in a DSA switch tree.
> If more than one CPU port is found in a tree, the code assigns CPU ports
> to user/DSA ports in a round robin way. So for the simplest case where
> we have one switch with N ports, 2 of them of type CPU connected to eth0
> and eth1, and the other ports labels being lan1, lan2, ..., the code
> assigns them to CPU ports this way:
>   lan1 <-> eth0
>   lan2 <-> eth1
>   lan3 <-> eth0
>   lan4 <-> eth1
>   lan5 <-> eth0

Hi Marek

That is what i've always argued is a good default. So i'm happy with
this.

> Patch 2 adds a new operation to the net device operations structure.
> Currently we use the iflink property of a net device to report to which
> CPU port a given switch port si connected to. The ip link utility from
> iproute2 reports this as "lan1@...0". We add a new net device operation,
> ndo_set_iflink, which can be used to set this property. We call this
> function from the netlink handlers.

That is a new idea. Interesting.

I would like to look around and see what else uses this "lan1@...0"
concept. We need to ensure it is not counter intuitive in general,
when you consider all possible users.

> Patch 3 implements this new ndo_set_iflink operation for DSA slave
> device. Thus the userspace can request a change of CPU port of a given
> port.

So this is all about transmit from the host out the switch. What about
receive? How do you tell the switch which CPU interface it should use
for a port?

    Thanks
	Andrew