netdev - Re: SRIOV switchdev mode BoF minutes

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Date:   Tue, 17 Apr 2018 10:47:00 -0400
From:   Andy Gospodarek <andrew.gospodarek@...adcom.com>
To:     Or Gerlitz <gerlitz.or@...il.com>
Cc:     Andy Gospodarek <andrew.gospodarek@...adcom.com>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        David Miller <davem@...emloft.net>,
        Anjali Singhai Jain <anjali.singhai@...el.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Simon Horman <simon.horman@...ronome.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        John Fastabend <john.fastabend@...il.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Rony Efraim <ronye@...lanox.com>,
        Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: SRIOV switchdev mode BoF minutes

On Tue, Apr 17, 2018 at 04:58:05PM +0300, Or Gerlitz wrote:
> On Tue, Apr 17, 2018 at 4:30 PM, Andy Gospodarek
> <andrew.gospodarek@...adcom.com> wrote:
> > On Mon, Apr 16, 2018 at 07:08:39PM -0700, Samudrala, Sridhar wrote:
> >>
> >> On 4/16/2018 5:39 AM, Andy Gospodarek wrote:
> >> > On Sun, Apr 15, 2018 at 09:01:16AM +0300, Or Gerlitz wrote:
> >> > > On Sat, Apr 14, 2018 at 2:03 AM, Samudrala, Sridhar
> >> > > <sridhar.samudrala@...el.com> wrote:
> >> > >
> >> > > > I meant between PFs on 2 compute nodes.
> >> > > If the PF serves as uplink rep, it functions as  a switch port -- applications
> >> > > don't run on switch ports. One way to get apps to run on the host in switchdev
> >> > > mode is probe one of the VFs there.
> >> > >
> >> > >
> >> > >
> >> So once a pci device is configured in 'switchdev' mode,  only port representor netdevs are
> >> seen on the host, no more PF netdev.
> >
> > That is not the functionality I would propose.  The PF netdev will still be there.
> 
> Andy,
> 
> Basically LGTM, so even in smartnic configs, the PF @ the host is
> still privileged to
> create/destroy VFs or provision MACs for them even if it is not the
> e-switch manager
> anymore?

Yes, in a SmartNIC world one config we aim to have is that a host can create
and destroy VFs as needed.  One of the challenges is how the VF reps are
managed by applications in the SmartNIC when the host could make them
disappear.  

> Actually AFAIK this  can also work somehow otherwise, e.g a smartnic FW
> "pushes" the VFs into the host w.o them being under a host admin directive.

The model to 'push' VFs to a host is also another option, but I do not
like it as much.  My general preference is to allow the host to use a
SmartNIC as if it was any other standard NIC (we have been using the
word 'Performance NIC' to desribe what we would call a standard NIC, but
the name is not terribly important).

There is also a school of thought that the VF reps could be
pre-allocated on the SmartNIC so that any application processing that
traffic would sit idle when no traffic arrives on the rep, but could
process frames that do arrive when the VFs were created on the host.
This implementation will depend on how resources are allocated on a
given bit of hardware, but can really work well.