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Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network d
From: |
Alex Williamson |
Subject: |
Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices |
Date: |
Mon, 20 May 2019 16:56:57 -0600 |
On Fri, 17 May 2019 14:58:16 +0200
Jens Freimann <address@hidden> wrote:
> This is another attempt at implementing the host side of the
> net_failover concept
> (https://www.kernel.org/doc/html/latest/networking/net_failover.html)
>
> Changes since last RFC:
> - work around circular dependency of commandline options. Just add
> failover=on to the virtio-net standby options and reference it from
> primary (vfio-pci) device with standby=<id>
> - add patch 3/4 to allow migration of vfio-pci device when it is part of a
> failover pair, still disallow for all other devices
> - add patch 4/4 to allow unplug of device during migrationm, make an
> exception for failover primary devices. I'd like feedback on how to
> solve this more elegant. I added a boolean to DeviceState, have it
> default to false for all devices except for primary devices.
> - not tested yet with surprise removal
> - I don't expect this to go in as it is, still needs more testing but
> I'd like to get feedback on above mentioned changes.
>
> The general idea is that we have a pair of devices, a vfio-pci and a
> emulated device. Before migration the vfio device is unplugged and data
> flows to the emulated device, on the target side another vfio-pci device
> is plugged in to take over the data-path. In the guest the net_failover
> module will pair net devices with the same MAC address.
>
> * In the first patch the infrastructure for hiding the device is added
> for the qbus and qdev APIs.
>
> * In the second patch the virtio-net uses the API to defer adding the vfio
> device until the VIRTIO_NET_F_STANDBY feature is acked.
>
> Previous discussion:
> RFC v1 https://patchwork.ozlabs.org/cover/989098/
> RFC v2 https://www.mail-archive.com/address@hidden/msg606906.html
>
> To summarize concerns/feedback from previous discussion:
> 1.- guest OS can reject or worse _delay_ unplug by any amount of time.
> Migration might get stuck for unpredictable time with unclear reason.
> This approach combines two tricky things, hot/unplug and migration.
> -> We can surprise-remove the PCI device and in QEMU we can do all
> necessary rollbacks transparent to management software. Will it be
> easy, probably not.
> 2. PCI devices are a precious ressource. The primary device should never
> be added to QEMU if it won't be used by guest instead of hiding it in
> QEMU.
> -> We only hotplug the device when the standby feature bit was
> negotiated. We save the device cmdline options until we need it for
> qdev_device_add()
> Hiding a device can be a useful concept to model. For example a
> pci device in a powered-off slot could be marked as hidden until the
> slot is
> powered on (mst).
> 3. Management layer software should handle this. Open Stack already has
> components/code to handle unplug/replug VFIO devices and metadata to
> provide to the guest for detecting which devices should be paired.
> -> An approach that includes all software from firmware to
> higher-level management software wasn't tried in the last years. This is
> an attempt to keep it simple and contained in QEMU as much as possible.
> 4. Hotplugging a device and then making it part of a failover setup is
> not possible
> -> addressed by extending qdev hotplug functions to check for hidden
> attribute, so e.g. device_add can be used to plug a device.
>
>
> I have tested this with a mlx5 NIC and was able to migrate the VM with
> above mentioned workarounds for open problems.
>
> 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="?
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?
Finally, please copy me on code touching vfio. Thanks,
Alex
- Re: [Qemu-devel] [PATCH 3/4] net/virtio: add failover support, (continued)
- Re: [Qemu-devel] [PATCH 3/4] net/virtio: add failover support, Dr. David Alan Gilbert, 2019/05/30
- Re: [Qemu-devel] [PATCH 3/4] net/virtio: add failover support, Michael S. Tsirkin, 2019/05/30
- Re: [Qemu-devel] [PATCH 3/4] net/virtio: add failover support, Dr. David Alan Gilbert, 2019/05/31
- Re: [Qemu-devel] [PATCH 3/4] net/virtio: add failover support, Eduardo Habkost, 2019/05/30
- Re: [Qemu-devel] [PATCH 3/4] net/virtio: add failover support, Dr. David Alan Gilbert, 2019/05/30
[Qemu-devel] [PATCH 2/4] qdev/qbus: Add hidden device support, Jens Freimann, 2019/05/17
[Qemu-devel] [PATCH 4/4] vfio/pci: unplug failover primary device before migration, Jens Freimann, 2019/05/17
Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices,
Alex Williamson <=
- Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices, Jens Freimann, 2019/05/21
- Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices, Michael S. Tsirkin, 2019/05/28
- Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices, Jens Freimann, 2019/05/29
- Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices, Michael S. Tsirkin, 2019/05/30
- Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices, Jens Freimann, 2019/05/31
Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices, Alex Williamson, 2019/05/21