netdev - RE: SRIOV switchdev mode BoF minutes

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Date:   Wed, 18 Apr 2018 17:07:02 +0000
From:   "Parikh, Neerav" <neerav.parikh@...el.com>
To:     Andy Gospodarek <andrew.gospodarek@...adcom.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     Or Gerlitz <gerlitz.or@...il.com>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        David Miller <davem@...emloft.net>,
        "Singhai, Anjali" <anjali.singhai@...el.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Simon Horman <simon.horman@...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



> -----Original Message-----
> From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org]
> On Behalf Of Andy Gospodarek
> Sent: Wednesday, April 18, 2018 8:15 AM
> To: Jakub Kicinski <jakub.kicinski@...ronome.com>
> Cc: Andy Gospodarek <andrew.gospodarek@...adcom.com>; Or Gerlitz
> <gerlitz.or@...il.com>; Samudrala, Sridhar <sridhar.samudrala@...el.com>;
> David Miller <davem@...emloft.net>; Singhai, Anjali
> <anjali.singhai@...el.com>; Michael Chan <michael.chan@...adcom.com>;
> Simon Horman <simon.horman@...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 04:19:15PM -0700, Jakub Kicinski wrote:
> > On Tue, 17 Apr 2018 10:47:00 -0400, Andy Gospodarek wrote:
> > > 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.
> >
> > +1 if there is no FW resource allocation issues IMHO it's okay to
> > just show all reprs for "remote PCIes (PFs and VFs)" on the SmartNIC/
> > controller.  The reprs should just show link down as if PCIe cable
> > was unpluged until host actually enables them.
> 
> Yes we are on the same page on this.
> 
> > A similar issue exists on multi-host for PFs, right?  If one of the
> > hosts is down do we still show their PF repr?  IMHO yes.
> 
> I would agree with that as well.  With today's model the VF reps are
> created once a PF is put into switchdev mode, but I'm still working out
> how we want to consider whether or not a PF rep for the other domains is
> created locally or not and also how one can determine which domain is in
> control.
> 
> Permanent config options (like NVRAM settings) could easily handle which
> domain is in control, but that still does not mean that PF reps must be
> created automatically, does it?
> 
> > That makes the thing looks more like a switch with cables being plugged
> > in and out.
> 
> Yes, that's exactly how I view it as well.

If we need to behave like a switch or emulate that mode then is there a 
thought around the usability model?

So, while whichever domain is in control the implication above is that the
max number of vports supported (VFs and PFs) will need to be represented
regardless of whether they're "Enabled" or not in a given "Switch".
By "Enabled" I mean SRIOV VFs may not have been enabled but still the
representor exists.
For example if there are 256 VFs supported on a given PF when someone
switches into the switchdev mode there will be ~257 representor netdevs
added into the system. And if you've multi-port, multi-function devices
the number of representor netdevs will increase accordingly.
While representor netdevs' naming may help a bit here but a user will 
need to determine and differentiate between the sprawl of representors
netdevs and data netdevs to identify which all can be added into an 
OVS bridge (or vSwitch).
And switching to the "switchdev mode" becomes a pre-requisite before
any of the vSwitch bridges that uses these representor netdevs.

While, in a SmartNIC where users are not managing the devices this may
be deployed based on the NIC FW/SW capabilities. 
But, I'm not sure how the same model applied on a standard host running 
Linux will work across devices.