netdev - Re: [patch net-next 00/12] net: expose switch ID via devlink

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Date:   Fri, 29 Mar 2019 15:34:14 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Linux Netdev List <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>, mlxsw@...lanox.com,
        Ido Schimmel <idosch@...lanox.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>, vivien.didelot@...il.com,
        Michael Chan <michael.chan@...adcom.com>,
        Or Gerlitz <ogerlitz@...lanox.com>
Subject: Re: [patch net-next 00/12] net: expose switch ID via devlink

On Fri, Mar 29, 2019 at 2:21 PM Jiri Pirko <jiri@...nulli.us> wrote:
> Fri, Mar 29, 2019 at 07:59:26PM CET, jakub.kicinski@...ronome.com wrote:
> >On Fri, 29 Mar 2019 07:49:05 +0100, Jiri Pirko wrote:
> >> Thu, Mar 28, 2019 at 10:40:02PM CET, jakub.kicinski@...ronome.com wrote:
> >> >On Thu, 28 Mar 2019 22:12:42 +0100, Jiri Pirko wrote:
> >> >> From: Jiri Pirko <jiri@...lanox.com>
> >> >>
> >> >> To provide visibility of the ports, this patchset exposes switch ID
> >> >> for devlink ports, which are part of a switch. The rest of the ports
> >> >> if any (in case of sr-iov for example) do not set switch ID.
> >> >
> >> >I don't feel good about this patch set.  There is no visibility
> >> >provided here.  Should the port flavour should be a sufficient
> >>
> >> 1) this patch is mainly about avoiding need to define the ndo and moving
> >>    the switch id definition to devlink port attr.
> >
> >Sure, that you could achieve by putting the data in the netdevice
> >structure as well..
> >
> >What is the guiding principle here?  I'm trying to argue for leaving
> >forwarding-related info in netdev code, and only have HW control in
> >devlink.  I just don't see switch id being useful at devlink level in
> >any way.
>
> Well we have switchib driver which does not have any netdevice and still
> the ports are part of a switch. In other words, this is not
> ethernet-specific attribute, therefore devlink is the right fit.

Ack, but switch id is a switchdev thing, controlling which ports are
considered to be part of the same device _for_ _switchdev_.

Is switchib doing forwarding?  Not long ago Parav was convincing us
that switchdev mode for IB is pretty much meaningless.  Even though
there are apparently representors for IB (judging by the recent RDMA
patchset on netdev)...

> >> 2) along with that, switch id is added as attribute. It tells the user
> >>    that some devlink port is part of a switch with certain id. If port
> >>    is not part of a switch (like upcoming hostport, cpu, dsa, etc),
> >>    switch id is not set on that port
> >
> >If the flavour already gives that information, why crowd the attributes
> >for ports with switch id?
>
> Hmm, we'll have multiple non-switch port flavours and once your vf/pf
> patchset  hits the tree we'll have multipkle switch port flavours.
> So makes sense to have switch id.

It's probably a matter of preference then.  To me its very clear to say that
you can switch to physical/vf/pf ports and not cpu/dsa/host. I don't like
the duplication of dumpnig the same attribute both in rtnetlink and devlink.

> Also, you can have multiple switches within one asic.

That line is blurry.

> >> >indication of whether netdev associated with that port can be
> >> >switched to or not?  CPU, DSA, and Host flavours can't be switched
> >> >to.  And the switchid can be an attribute of the devlink instance,
> >> >if we want to expose it via devlink.
> >>
> >> One devlink instance can have multiple switch ids in use as it may
> >> contain multiple switches. Take mlx5 as an instance. Currently every PF
> >> creates a separate devlink instance, however there are some features
> >> shared. In this example, with proposed idea of aliasing, there would be
> >> one devlink instance aliased between these 2 pf inctances, with 2
> >> eswitches and 2 sets of switch ports each belonging to an eswitch -
> >> distinguished by switch id.
> >
> >Out of curiosity, what are the shared features?  It seems mlx5 drives
> >a lot of our API design, it'd be good if the community had a better
> >understanding of it.
>
> I have to gather that info. Not so many things are shared. There is one
> extra switch to mix 2 pfs together. I know about some IB features that
> also mix 2 pfs.

I see, so a dual port IB card would somehow have only one whatever the
equivalent of a netdev in IB world is?

> >The situation with pipelined devices is somewhat murky.  Didn't Or add
> >some from of PCIe-side looped queue to forward between PFs?
>
> I have no clue. Ccing Or. Or?
>
> >Presumably DSA would lean the opposite way with multiple ASICs
> >reporting the same ID?
>
> Yes, sounds right.

Right, so to me switch ID really is a forwarding attribute.