Public bug reported:
# Summary
Upstream VirGL video acceleration support in virglrenderer requires the
VMM (QEMU) to explicitly enable it by passing the
VIRGL_RENDERER_USE_VIDEO flag during virglrenderer initialization.
Ubuntu currently builds virglrenderer with video disabled (tracked in LP
#2141692). Even after LP #2141692 is resolved, guests will not be able
to use VirGL video acceleration unless Ubuntu QEMU enables (or provides
an opt-in switch to enable) VIRGL_RENDERER_USE_VIDEO.
# Related bug
- virglrenderer build feature request: LP #2141692
# Background / Motivation
VirGL video acceleration aims to expose VA-API video encode/decode
capabilities to virtio-gpu/virgl guests (where supported by host
GPU/driver stack). This can reduce guest CPU load and improve multimedia
and remote desktop streaming responsiveness in VM desktops.
virglrenderer alone is not sufficient: QEMU must pass a runtime flag to
activate the video path.
# Request
Please add support in Ubuntu QEMU to enable VirGL video acceleration by
passing VIRGL_RENDERER_USE_VIDEO when initializing virglrenderer for
virtio-gpu virgl/virtio-gpu-gl.
To minimize risk/regressions, please implement this as an OPT-IN feature
(default off), e.g.:
- a device property on virtio-gpu-gl / virtio-vga-gl such as "virgl-video=on"
(naming up to maintainer)
- when enabled, QEMU includes VIRGL_RENDERER_USE_VIDEO in the flags passed to
virgl_renderer_init()
# Notes / Scope
- This bug is about QEMU plumbing/runtime flag control only.
- The virglrenderer build-time enablement is tracked separately in LP #2141692.
Both are required for end-to-end testing.
# Evidence / How to verify on Ubuntu
On an Ubuntu host:
1) Enable virglrenderer video feature (via LP #2141692 fix or locally rebuilt
virglrenderer).
2) With QEMU supporting the opt-in flag, start a VM with virtio-gpu +
virgl/virtio-gl and set the new property.
3) In the guest:
LIBVA_DRIVER_NAME=virtio_gpu vainfo
Expected:
- virtio_gpu VA-API driver loads
- Additional codec profiles (decode/encode depending on host capabilities)
appear vs baseline
# Why opt-in is preferred
- Avoids enabling a newer/less widely tested code path for all users by default.
- Allows targeted testing across Intel/AMD/NVIDIA and different Mesa/driver
stacks during the 26.04 cycle.
- Provides a clean upgrade path: opt-in now; consider default-on later if
stable.
# References
- virglrenderer video feature needs VMM runtime flag VIRGL_RENDERER_USE_VIDEO
(per upstream documentation / common downstream patches)
- Related Ubuntu request: LP #2141692
** Affects: qemu (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2141694
Title:
Add opt-in support to enable VIRGL_RENDERER_USE_VIDEO for virtio-gpu
virgl
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