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

On Fri, Mar 02, 2018 at 02:26:48PM -0800, Siwei Liu wrote:

On Fri, Mar 2, 2018 at 1:31 PM, Michael S. Tsirkin [off-list ref] wrote:

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On Fri, Mar 02, 2018 at 12:44:56PM -0800, Siwei Liu wrote:

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On Fri, Mar 2, 2018 at 12:10 PM, Michael S. Tsirkin [off-list ref] wrote:

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On Fri, Mar 02, 2018 at 11:52:27AM -0800, Samudrala, Sridhar wrote:

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On 3/2/2018 11:41 AM, Michael S. Tsirkin wrote:

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On Fri, Mar 02, 2018 at 07:26:25AM -0800, Alexander Duyck wrote:

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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.

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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

Interesting point. I guess that's a limitation in the curent patch then:
virtio and PT device must be connected to the same physical NIC.
Worth documenting.

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--
MST

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