cc59698d69
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>
10 lines
432 B
YAML
10 lines
432 B
YAML
---
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features:
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- |
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From this release, Nova instances will get ``virtio`` as the default
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display device (instead of ``cirrus``, which has many limitations).
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If your guest has a native kernel (called "virtio-gpu" in Linux;
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available since Linux 4.4 and above) driver, then it'll be used;
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otherwise, the 'virtio' model will gracefully fallback to VGA
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compatibiliy mode, which is still better than ``cirrus``.
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