netdev - Re: [RFC] virtio-net: help live migrate SR-IOV devices

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Date:   Tue, 5 Dec 2017 13:52:26 -0800
From:   Jesse Brandeburg <jesse.brandeburg@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     achiad shochat <achiad.mellanox@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Hannes Frederic Sowa <hannes@...hat.com>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        <virtualization@...ts.linux-foundation.org>,
        Shannon Nelson <shannon.nelson@...cle.com>,
        Achiad <achiad@...lanox.com>,
        "Peter Waskiewicz Jr" <peter.waskiewicz.jr@...el.com>,
        netdev <netdev@...r.kernel.org>,
        Anjali Singhai Jain <anjali.singhai@...el.com>,
        Andy Gospodarek <gospo@...adcom.com>,
        Or Gerlitz <gerlitz.or@...il.com>, jesse.brandeburg@...el.com
Subject: Re: [RFC] virtio-net: help live migrate SR-IOV devices

On Tue, 5 Dec 2017 21:20:07 +0200
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> On Tue, Dec 05, 2017 at 11:59:17AM +0200, achiad shochat wrote:
> > Then we'll have a single solution for both netvsc and virtio (and any
> > other PV device).
> > And we could handle the VF DMA dirt issue agnostically.  
> 
> For the record, I won't block patches adding this kist to virtio
> on the basis that they must be generic. It's not a lot
> of code, implementation can come first, prettify later.

Thanks, based on this discussion we're going to work on improving
virtio-net first, but some of Achiad's points are good.  I don't believe
it should block the virtio work however.

In particular I'm really interested in figuring out how we can get to
the point that virtio is able to make or implement some smart decisions
about which NIC to pick for traffic delivery (it's own paravirt path or
the passthorugh device path), if Achiad wants to develop the idea into
some code, I'd be interested to review it.

> But we do need to have a discussion about how devices are paired.
> I am not sure using just MAC works. E.g. some passthrough
> devices don't give host ability to set the MAC.
> Are these worth worrying about?

I personally don't think that will be much of a problem, if a
certain device has that issue, can't we just have the virtio-net device
pick up the MAC address of the passthrough device? As long as they match
things should work OK. It at least is an initial way to do the
configuration that has at least some traction as workable, as proved by
the Microsoft design.

FWIW, the Intel SR-IOV devices all accept a hypervisor/host provided
MAC address.