netdev - Re: [virtio-dev] Re: [PATCH v4 2/2] virtio_net: Extend virtio to use VF datapath when available

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Date:   Fri, 2 Mar 2018 14:26:48 -0800
From:   Siwei Liu <loseweigh@...il.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Stephen Hemminger <stephen@...workplumber.org>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>, virtio-dev@...ts.oasis-open.org,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        Jakub Kicinski <kubakici@...pl>
Subject: Re: [virtio-dev] Re: [PATCH v4 2/2] virtio_net: Extend virtio to use
 VF datapath when available

On Fri, Mar 2, 2018 at 1:31 PM, Michael S. Tsirkin <mst@...hat.com> wrote:
> On Fri, Mar 02, 2018 at 12:44:56PM -0800, Siwei Liu wrote:
>> On Fri, Mar 2, 2018 at 12:10 PM, Michael S. Tsirkin <mst@...hat.com> wrote:
>> > On Fri, Mar 02, 2018 at 11:52:27AM -0800, Samudrala, Sridhar wrote:
>> >>
>> >>
>> >> On 3/2/2018 11:41 AM, Michael S. Tsirkin wrote:
>> >> > On Fri, Mar 02, 2018 at 07:26:25AM -0800, Alexander Duyck wrote:
>> >> > > The design limits things to a 1:1 relationship since we just have the
>> >> > > child and backup pointers, but I don't think I am seeing exception
>> >> > > handling to prevent us from overwriting the child pointers so there
>> >> > > may be a leak there.
>> >> > >
>> >> > > Thanks.
>> >> > >
>> >> > > - Alex
>> >> > In fact maintaining a list in that case would be nicer, and
>> >> > just use an arbitrary one.
>> >> > E.g. one can see how a user wanting to swap device 1 for device 2
>> >> > might first add device 2 with same MAC then drop device 1.
>> >>
>> >> It should be possible to swap VF1 with VF2 by
>> >> 1.- enabling virtio link
>> >> 2.- unplugging VF1
>> >> 3.- plugging VF2
>> >> 4.- disabling virtio link
>> >>
>> >
>> > True, but it isn't hard to avoid breakage if user
>> > swapped steps 2 and 3. No need to make it more
>> > fragile that it has to be.
>>
>> The migration case, VF2 is associated with another PF on another
>> machine (destination), I wonder how it is possible.
>
> E.g. you want to remove the PF so you unplug the VF
> then add another VF of the same PF.
>
>> Even with local plugging of VF2 on the same PF, the MAC address
>> requirement (VF1's == VF2's) would fail the MAC address assignment on
>> VF2.
>>
>> -Siwei
>
> Why would it fail? These are separate cards.

OK. I realized that you may talk about assigning a VF on a diffferent
PF (VF1 on PF1 while VF2 on PF2). And we might assign a pass-through
device rather than a VF. Yes, it's indeed possible that may happen but
I take it as a further step down (another patch maybe) as it would
involve changes to notify the network with gratuituious ARP and/or
unsolicited ND advertisement of the MAC address association with the
new port.

-Siwei

>
>> >
>> > --
>> > MST
>> >
>> > ---------------------------------------------------------------------
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>> >