Re: [RFC PATCH V2 00/10] Qemu: Add live migration support for SRIOV NIC

["Lan, Tianyu" <tianyu.lan@intel.com>]

On 11/30/2015 4:01 PM, Michael S. Tsirkin wrote:
> It is still not very clear what it is you are trying to achieve, and
> whether your patchset achieves it.  You merely say "adding live
> migration" but it seems pretty clear this isn't about being able to
> migrate a guest transparently, since you are adding a host/guest
> handshake.
>
> This isn't about functionality either: I think that on KVM, it isn't
> hard to live migrate if you can do a host/guest handshake, even today,
> with no kernel changes:
> 1. before migration, expose a pv nic to guest (can be done directly on
>    boot)
> 2. use e.g. a serial connection to move IP from an assigned device to pv nic
> 3. maybe move the mac as well
> 4. eject the assigned device
> 5. detect eject on host (QEMU generates a DEVICE_DELETED event when this
>     happens) and start migration
>

This looks like the bonding driver solution which put pv nic and VF
in one bonded interface under active-backup mode. The bonding driver
will switch from VF to PV nic automatically when VF is unplugged during
migration. This is the only available solution for VF NIC migration. But
it requires guest OS to do specific configurations inside and rely on
bonding driver which blocks it work on Windows. From performance side,
putting VF and virtio NIC under bonded interface will affect their
performance even when not do migration. These factors block to use VF
NIC passthough in some user cases(Especially in the cloud) which require
migration.

Current solution we proposed changes NIC driver and Qemu. Guest Os
doesn't need to do special thing for migration. It's easy to deploy and
all changes are in the NIC driver, NIC vendor can implement migration
support just in the their driver.