On Fri, Jan 24, 2020 at 10:39:18AM -0500, Laine Stump wrote: > The QEMU driver uses the <teaming type='persistent|transient' > persistent='blah'/> element to setup a "failover" pair of devices - > the persistent device must be a virtio emulated NIC, with the only > extra configuration being the addition of ",failover=on" to the device > commandline, and the transient device must be a hostdev NIC > (<interface type='hostdev'> or <interface type='network'> with a > network that is a pool of SRIOV VFs) where the extra configuration is > the addition of ",failover_pair_id=$aliasOfVirtio" to the device > commandline. These new options are supported in QEMU 4.2.0 and later. > > Extra qemu-specific validation is added to ensure that the device > type/model is appropriate and that the qemu binary supports these > commandline options. > > The result of this will be: > > 1) The virtio device presented to the guest will have an extra bit set > in its PCI capabilities indicating that it can be used as a failover > backup device. The virtio guest driver will need to be equipped to do > something with this information. Unfortunately there is no way for > libvirt to learn whether or not the guest driver supports failover - > if it doesn't then the extra PCI capability will be ignored and the > guest OS will just see two independent devices. (NB: the current > virtio guest driver also requires that the MAC addresses of the two > NICs match in order to pair them into a bond). > > 2) When a migration is requested, QEMu will automatically unplug the > transient/hostdev NIC from the guest on the source host before > starting migration, and automatically re-plug a similar device after > restarting the guest CPUs on the destination host. While the transient > NIC is unplugged, all network traffic will go through the > persistent/virtio device, but when the hostdev NIC is plugged in, it > will get all the traffic. This means that in normal circumstances the > guest gets the performance advantage of vfio-assigned "real hardware" > networking, but it can still be migrated with the only downside being > a performance penalty (due to using an emulated NIC) during the > migration. > > Signed-off-by: Laine Stump <laine@xxxxxxxxxx> > --- > src/qemu/qemu_command.c | 9 +++++ > src/qemu/qemu_domain.c | 36 +++++++++++++++-- > .../qemuxml2argvdata/net-virtio-teaming.args | 40 +++++++++++++++++++ > tests/qemuxml2argvtest.c | 4 ++ > 4 files changed, 86 insertions(+), 3 deletions(-) > create mode 100644 tests/qemuxml2argvdata/net-virtio-teaming.args Reviewed-by: Daniel P. Berrangé <berrange@xxxxxxxxxx> Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
