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

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Date:   Fri, 29 Mar 2019 11:59:26 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, mlxsw@...lanox.com,
        idosch@...lanox.com, f.fainelli@...il.com, andrew@...n.ch,
        vivien.didelot@...il.com, michael.chan@...adcom.com
Subject: Re: [patch net-next 00/12] net: expose switch ID via devlink

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.

> 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?

> >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.

The situation with pipelined devices is somewhat murky.  Didn't Or add
some from of PCIe-side looped queue to forward between PFs?

Presumably DSA would lean the opposite way with multiple ASICs
reporting the same ID?