Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices

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

On Tue, May 28, 2019 at 05:14:22PM -0700, si-wei liu wrote:
> 
> 
> On 5/21/2019 11:49 AM, Jens Freimann wrote:
> > On Tue, May 21, 2019 at 07:37:19AM -0400, Michael S. Tsirkin wrote:
> > > On Tue, May 21, 2019 at 09:21:57AM +0200, Jens Freimann wrote:
> > > > On Mon, May 20, 2019 at 04:56:57PM -0600, Alex Williamson wrote:
> > > > > On Fri, 17 May 2019 14:58:16 +0200
> > > > > Jens Freimann <jfreimann@redhat.com> wrote:
> > > > > > Command line example:
> > > > > >
> > > > > > qemu-system-x86_64 -enable-kvm -m 3072 -smp 3 \
> > > > > >         -machine q35,kernel-irqchip=split -cpu host   \
> > > > > >         -k fr   \
> > > > > >         -serial stdio   \
> > > > > >         -net none \
> > > > > >         -qmp unix:/tmp/qmp.socket,server,nowait \
> > > > > >         -monitor telnet:127.0.0.1:5555,server,nowait \
> > > > > >         -device
> > > > pcie-root-port,id=root0,multifunction=on,chassis=0,addr=0xa \
> > > > > >         -device pcie-root-port,id=root1,bus=pcie.0,chassis=1 \
> > > > > >         -device pcie-root-port,id=root2,bus=pcie.0,chassis=2 \
> > > > > >         -netdev
> > > > tap,script=/root/bin/bridge.sh,downscript=no,id=hostnet1,vhost=on
> > > > \
> > > > > >         -device virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:6f:55:cc,bus=root2,failover=on
> > > > \
> > > > > >         /root/rhel-guest-image-8.0-1781.x86_64.qcow2
> > > > > >
> > > > > > Then the primary device can be hotplugged via
> > > > > >  (qemu) device_add
> > > > vfio-pci,host=5e:00.2,id=hostdev0,bus=root1,standby=net1
> > > > >
> > > > > Is this standby= option only valid for Network/Ethernet class code
> > > > > devices?  If so, perhaps vfio-pci code should reject the
> > > > option on any
> > > > > non-ethernet devices.  The option is also non-intuitive for
> > > > users, only
> > > > > through examples like above can we see it relates to the id of the
> > > > > secondary device.  Could we instead name it something like
> > > > > "standby_net_failover_pair_id="?
> > > > 
> > > > It is only for ethernet (VFs), I will add code to reject
> > > > non-ethernet VF devices.
> > > > I agree the name is not descriptive and the one you suggest
> > > > seems good to
> > > > me.
> > > > >
> > > > > Also, this feature requires matching MAC addresses per the
> > > > description,
> > > > > where is that done?  Is it the user's responsibility to set
> > > > the MAC on
> > > > > the host device prior to the device_add?  If so, is this actually not
> > > > > only specific to ethernet devices, but ethernet VFs?
> > > > 
> > > > Yes, it's the users responsibility and the MACs are then matched by
> > > > the net_failover driver in the guest. It makes sense for
> > > > ethernet VFs only,
> > > > I'll add a check for that.
> > > 
> > > Actually is there a list of devices for which this has been tested
> > > besides mlx5? I think someone said some old intel cards
> > > don't support this well, we might need to blacklist these ...
> > 
> > So far I've tested mlx5 and XL710 which both worked, but I'm
> > working on testing with more devices. But of course help with testing
> > is greatly appreciated.
> It won't work on Intel ixgbe and Broadcom bnxt_en, which requires toggling
> the state of tap backing the virtio-net in order to release/reprogram MAC
> filter. Actually, it's very few NICs that could work with this - even some
> works by chance the behavior is undefined. Instead of blacklisting it makes
> more sense to whitelist the NIC that supports it - with some new sysfs
> attribute claiming the support presumably.
> 
> -Siwei

I agree for many cards we won't know how they behave until we try.  One
can consider this a bug in Linux that cards don't behave in a consistent
way.  The best thing to do IMHO would be to write a tool that people can
run to test the behaviour.


> > 
> > regards,
> > Jens