netdev - Re: [PATCH net-next] net: Add phys_port identifier to struct net

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Date:	Tue, 2 Jul 2013 07:40:40 -0700
From:	<Narendra_K@...l.com>
To:	<bhutchings@...arflare.com>
CC:	<john.fastabend@...il.com>, <netdev@...r.kernel.org>,
	<john.r.fastabend@...el.com>
Subject: Re: [PATCH net-next] net: Add phys_port identifier to struct
 net_device and export it to sysfs

On Fri, Jun 28, 2013 at 10:39:13PM +0530, Ben Hutchings wrote:
> 
> On Fri, 2013-06-28 at 09:33 -0700, John Fastabend wrote:
[...]
> > > John, I think it will be useful in the SRIOV scenario also when more
> > than one VF from two NICs are assigned to the guest. phys_port would be
> > helpful in choosing the correct slave interfaces when host details are
> > not available.
> >
> > OK. But I'm not sure why you would assign two VFs from the same NIC
> > to a guest? This doesn't seem like a good configuration for failover
> > because if one VF fails it seems likely both will fail. Maybe there
> > are some benefits for load balancing? Or my assumption both VFs will
> > fail is wrong.
> 
> I believe Narendra is trying to provide hints to the guest that would
> allow it to avoid such broken bonding configurations.  But it is
> certainly a good question why there would be two VFs assigned in the
> first place.
> 
> I could imagine passing through two VFs for the same physical port that
> have been assigned to different VLANs.  But then you wouldn't want to
> bond two devices that are on different VLANs, whether or not they're
> using the same port!

I was thinking of the following scenario in the guest. 

bond0 = NIC1 VF0 + NIC2 VF0
bond1 = NIC1 VF1 + NIC2 VF1

bond0 and bond1 are on different VLANs. The phys_port identifier hint
would be helpful to the guest in selecting the correct slaves for the
above configuration. Sorry if I missed any detail here.

> 
> > Anyways it does seem useful in the partitioning case with multiple
> > physical functions.

Yes, I agree. 

> 
> I was thinking it could also help to support the hybrid guest networking
> mode.  In this mode, the guest gets a PV (e.g. virtio_net) device and a
> VF bridged to the same physical port, and the VF can be removed before
> the guest is migrated (and maybe reinserted if there's a VF available on
> the new host) without a major disruption to the guest.  In that case the
> guest *should* bond together the two net devices that have the same
> physical port ID but different drivers.  This would require the physical
> port ID to be propagated through macvtap/macvlan and virtio.
> 
> Ben.
> 
> --
> Ben Hutchings, Staff Engineer, Solarflare
> Not speaking for my employer; that's the marketing department's job.
> They asked us to note that Solarflare product names are trademarked.
> 
> --
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> 

-- 
With regards,
Narendra K
Linux Engineering
Dell Inc.
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