openstack/nova
Code Issues Proposed changes

libvirt: Switch the default video model from 'cirrus' to 'virtio'

Browse Source 
The current Nova default video device model of 'cirrus' was chosen by
commit 2c7dca4ede (Configuration element for describing video drivers,
2013-11-25).  While it has worked fine-enough for all these years,
Cirrus devices is is "considered harmful"[1] by QEMU graphics
maintainers since 2014.

The current recommended video device model for both UEFI and BIOS guests
is 'virtio'[1].  'virtio' is a sensible default whether or not the guest
has a native kernel (called "virtio-gpu" in Linux) driver -- i.e. if the
guest has the VirtIO GPU driver, then it'll be used; otherwise, the
'virtio' model falls back to VGA compatibiliy mode.

To quote the documentation[2] from a QEMU graphics maintainer:

    This ['virtio' in libvirt or 'virtio-vga' in QEMU terms] is a
    modern, virtio-based display device designed for virtual machines.
    It comes with VGA compatibility mode. You need a guest driver to
    make full use of this device. If your guest OS has no driver it
    should still show a working display thanks to the VGA compatibility
    mode, but the device will not provide any advantages over standard
    VGA then.  [...] This is the place where most development happens,
    support for new, cool features will most likely be added to this
    device.

[1] "qemu: using cirrus considered harmful"
    https://www.kraxel.org/blog/2014/10/qemu-using-cirrus-considered-harmful/

[2] https://www.kraxel.org/blog/2019/09/display-devices-in-qemu/#virtio-vga

Implements: blueprint virtio-as-default-display-device

Change-Id: I4c999bb4120768af40093ddb1e6004ee33c9698f
Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
This commit is contained in:
Kashyap Chamarthy 2021-06-22 13:20:57 +02:00
parent 5979c64846
commit cc59698d69
3 changed files with 19 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
nova/virt/libvirt/config.py
View File

@ -2055,7 +2055,7 @@ class LibvirtConfigGuestVideo(LibvirtConfigGuestDevice):
super(LibvirtConfigGuestVideo, self).__init__(root_name="video",
**kwargs)
self.type = 'cirrus'
self.type = 'virtio'
self.vram = None
self.heads = None
self.driver_iommu = False

9
nova/virt/libvirt/driver.py
View File

@ -5920,6 +5920,15 @@ class LibvirtDriver(driver.ComputeDriver):
guestarch = libvirt_utils.get_arch(image_meta)
if CONF.libvirt.virt_type == 'parallels':
video.type = 'vga'
# NOTE(kchamart): 'virtio' is a sensible default whether or not
# the guest has the native kernel driver (called "virtio-gpu" in
# Linux) -- i.e. if the guest has the VirtIO GPU driver, it'll
# be used; otherwise, the 'virtio' model will gracefully
# fallback to VGA compatibiliy mode.
elif (guestarch in (fields.Architecture.I686,
fields.Architecture.X86_64) and not
CONF.spice.enabled):
video.type = 'virtio'
elif guestarch in (fields.Architecture.PPC,
fields.Architecture.PPC64,
fields.Architecture.PPC64LE):

9
releasenotes/notes/virtio-as-default-display-device-5341d3d5180036e2.yaml Normal file
View File

@ -0,0 +1,9 @@
---
features:
- |
From this release, Nova instances will get ``virtio`` as the default
display device (instead of ``cirrus``, which has many limitations).
If your guest has a native kernel (called "virtio-gpu" in Linux;
available since Linux 4.4 and above) driver, then it'll be used;
otherwise, the 'virtio' model will gracefully fallback to VGA
compatibiliy mode, which is still better than ``cirrus``.