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

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Dec 02, 2015 at 10:08:25PM +0800, Lan, Tianyu wrote:
> On 12/1/2015 11:02 PM, Michael S. Tsirkin wrote:
> >>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.
> >
> >That's really up to guest. You don't need to do bonding,
> >you can just move the IP and mac from userspace, that's
> >possible on most OS-es.
> >
> >Or write something in guest kernel that is more lightweight if you are
> >so inclined. What we are discussing here is the host-guest interface,
> >not the in-guest interface.
> >
> >>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
> >
> >
> >Except of course these patches don't even work properly yet.
> >
> >And when they do, even minor changes in host side NIC hardware across
> >migration will break guests in hard to predict ways.
> 
> Switching between PV and VF NIC will introduce network stop and the
> latency of hotplug VF is measurable.
> For some user cases(cloud service
> and OPNFV) which are sensitive to network stabilization and performance,
> these are not friend and blocks SRIOV NIC usage in these case.

I find this hard to credit. hotplug is not normally a data path
operation.

> We hope
> to find a better way to make SRIOV NIC work in these cases and this is
> worth to do since SRIOV NIC provides better network performance compared
> with PV NIC.

If this is a performance optimization as the above implies,
you need to include some numbers, and document how did
you implement the switch and how did you measure the performance.

> Current patches have some issues. I think we can find
> solution for them andimprove them step by step.

-- 
MST