netdev - Re: [PATCH net-next v9 3/4] virtio_net: Extend virtio to use VF datapath when available

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Date:   Sat, 28 Apr 2018 10:24:33 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Sridhar Samudrala <sridhar.samudrala@...el.com>
Cc:     mst@...hat.com, stephen@...workplumber.org, davem@...emloft.net,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org, jesse.brandeburg@...el.com,
        alexander.h.duyck@...el.com, kubakici@...pl, jasowang@...hat.com,
        loseweigh@...il.com, aaron.f.brown@...el.com
Subject: Re: [PATCH net-next v9 3/4] virtio_net: Extend virtio to use VF
 datapath when available

Fri, Apr 27, 2018 at 07:06:59PM CEST, sridhar.samudrala@...el.com wrote:
>This patch enables virtio_net to switch over to a VF datapath when a VF
>netdev is present with the same MAC address. It allows live migration
>of a VM with a direct attached VF without the need to setup a bond/team
>between a VF and virtio net device in the guest.
>
>The hypervisor needs to enable only one datapath at any time so that
>packets don't get looped back to the VM over the other datapath. When a VF

Why? Both datapaths could be enabled at a time. Why the loop on
hypervisor side would be a problem. This in not an issue for
bonding/team as well.


>is plugged, the virtio datapath link state can be marked as down. The
>hypervisor needs to unplug the VF device from the guest on the source host
>and reset the MAC filter of the VF to initiate failover of datapath to

"reset the MAC filter of the VF" - you mean "set the VF mac"?


>virtio before starting the migration. After the migration is completed,
>the destination hypervisor sets the MAC filter on the VF and plugs it back
>to the guest to switch over to VF datapath.
>
>It uses the generic failover framework that provides 2 functions to create
>and destroy a master failover netdev. When STANDBY feature is enabled, an
>additional netdev(failover netdev) is created that acts as a master device
>and tracks the state of the 2 lower netdevs. The original virtio_net netdev
>is marked as 'standby' netdev and a passthru device with the same MAC is
>registered as 'primary' netdev.
>
>This patch is based on the discussion initiated by Jesse on this thread.
>https://marc.info/?l=linux-virtualization&m=151189725224231&w=2

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