netdev - Re: [PATCH net-next v2 4/7] devlink: allow subports on devlink PCI ports

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Message-ID: <20190315181620.341bd02c@cakuba.netronome.com>
Date:   Fri, 15 Mar 2019 18:16:20 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Parav Pandit <parav@...lanox.com>
Cc:     Jiri Pirko <jiri@...nulli.us>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "oss-drivers@...ronome.com" <oss-drivers@...ronome.com>
Subject: Re: [PATCH net-next v2 4/7] devlink: allow subports on devlink PCI
 ports

On Fri, 15 Mar 2019 22:12:13 +0000, Parav Pandit wrote:
> > On Fri, 15 Mar 2019 21:08:14 +0100, Jiri Pirko wrote:  
> > > >> IIUC, Jiri/Jakub are proposing creation of 2 devlink objects for
> > > >> each port - host facing ports and switch facing ports. This is in
> > > >> addition to the netdevs that are created today.  
> > 
> > To be clear I'm not in favour of the dual-object proposal.
> >   
> > > >I am not proposing any different.
> > > >I am proposing only two changes.
> > > >1. control hostport params via referring hostport (not via indirect
> > > >peer)  
> > >
> > > Not really possible. If you passthrough VF into VM, the hostport goes
> > > along with it.
> > >  
> > > >2. flavour should not be vf/pf, flavour should be hostport, switchport.
> > > >Because switch is flat and agnostic of pf/vf/mdev.  
> > >
> > > Not sure. It's good to have this kind of visibility.  
> > 
> > Yes, this subthread honestly makes me go from 60% sure to 95% sure we
> > shouldn't do the dual object thing :(  Seems like Parav is already confused by
> > it and suggests host port can exist without switch port :(
> >  
> I am almost sure that I am not confused.
> I am clear that hostports should be configured by devlink
> instance which has the capability to program it.

Right now a devlink port is something that the datapath of an ASIC can
address.  All flavours we have presently are basically various MACs -
physical (front panel ports), DSA - for ASIC interconnects on a
multi-ASIC board, CPU - for connecting to a MAC of a NIC.

Jiri's flavour proposal was strictly extending the same logic to
SR-IOV.  Each object addressable within the datapath gets a port.  
The datapath's ID can be used as port_index.

I just reimplemented his patches here and added the subports which I
think he wasn't aware of as they are a quirk of old NFP ASICs.

Having 3 objects for the same datapath ID is a significant departure
from the existing devlink port semantics.

> When hostport is in VF, that VF usually won't have privilege
> to program it and won't have visibility to eswitch either.

If VM has no visibility into the eswitch and no permission to configure
things, what use does the object serve?

> Why would you like to start with restrictive model of peer view only?

"Restrictive model" is one way of putting it.  I'd rather say that we
are not adding objects which:
 (a) do not adhere to current semantics;
 (b) have no distinct function.

We can make the "add MAC address" command not use the word peer:

devlink port addr_pool add pci/0000:05:00.0/10003 type eth 00:11:22:33:44:55
devlink port addr_pool del pci/0000:05:00.0/10003 type eth 00:11:22:33:44:55

if the "peer" doesn't sit right.

> Hostports exist for infiniband HCA without switchport.
> We should be able to manage hostport objects without creating fake eswitch sw object.

It sounds like the RDMA subsystem is lacking a model to represent all
its objects, but that's RDMA's problem to solve..

In netdev world we have netdevs for ports which a used for bulk of the
configuration, most importantly - forwarding.

> Jakub,
> Can you please point to some example other than veth-pair where you
> configure host param (such as mac address) through a switch?

Existing "legacy" SR-IOV NDOs.

> An existing example will help me to map it to devlink eswitch proposal.
> If we go peer programming route, what are your thoughts on
> how should we program infiniband hostports which doesn't have peer ports?

Again, you may be trying to fix RDMA's lack of control objects, which
may be better fixed elsewhere..