Re: [PATCH v4 0/5] Support virtio-gpu DRM native context

["Alex Bennée" <alex.bennee@linaro.org>]

Dmitry Osipenko <dmitry.osipenko@collabora.com> writes:

> This patchset adds DRM native context support to VirtIO-GPU on Qemu.
>
> Contarary to Virgl and Venus contexts which mediate high level GFX APIs,
> DRM native context [1] mediates lower level kernel driver UAPI, which
> reflects in a less CPU overhead and less/simpler code needed to support it.
> DRM context consists of a host and guest parts that have to be implemented
> for each GPU driver. On a guest side, DRM context presents a virtual GPU as
> a real/native host GPU device for GL/VK applications.
>
> [1] https://www.youtube.com/watch?v=9sFP_yddLLQ
>
> Today there are four known DRM native context drivers existing in a wild:
>
>   - Freedreno (Qualcomm SoC GPUs), completely upstreamed
>   - AMDGPU, mostly merged into upstreams
>   - Intel (i915), merge requests are opened
>   - Asahi (Apple SoC GPUs), WIP status
>
>
> # How to try out DRM context:
>
> 1. DRM context uses host blobs and requires latest developer version 
> of Linux kernel [2] that has necessary KVM fixes.
>
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/
>
> 2. Use latest libvirglrenderer from upstream git/main for Freedreno
> and AMDGPU native contexts. For Intel use patches [3].
>
> [3] https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/1384
>

Can we detect if virglrenderer has support at build time?

  [drm] pci: virtio-gpu-pci detected at 0000:00:02.0
  [drm] Host memory window: 0x8000000000 +0x100000000
  [drm] features: +virgl +edid +resource_blob +host_visible
  [drm] features: +context_init
  [drm] number of scanouts: 1
  [drm] number of cap sets: 2
  DRM native context support was not enabled in virglrenderer
  qemu: virgl could not be initialized: -1
  [drm:virtio_gpu_init] *ERROR* timed out waiting for cap set 0

is a poor failure mode at runtime.

> 3. On guest, use latest Mesa version for Freedreno. For AMDGPU use
> Mesa patches [4], for Intel [5].
>
> [4] https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21658
> [5] https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29870
>
> 4. On guest, use latest Linux kernel v6.6+. Apply patch [6] if you're
>    running Xorg in guest.
>
> [6] https://lore.kernel.org/dri-devel/20241020224725.179937-1-dmitry.osipenko@collabora.com/
>
> Example Qemu cmdline that enables DRM context:
>
>   qemu-system-x86_64 -device virtio-vga-gl,hostmem=4G,blob=on,drm_native_context=on \
>       -machine q35,accel=kvm,memory-backend=mem1 \
>       -object memory-backend-memfd,id=mem1,size=8G -m 8G
>
>
> # Note about known performance problem in Qemu:
>
> DRM contexts are mapping host blobs extensively and these mapping
> operations work slowly in Qemu. Exact reason is unknown. Mappings work
> fast on Crosvm For DRM contexts this problem is more visible than for
> Venus/Virgl.
>
> Changelog:
>
> v4: - Improved SDL2/dmabuf patch by reusing existing Meson X11 config 
>       option, better handling EGL error and extending comment telling
>       that it's safe to enable SDL2 EGL preference hint. As was suggested
>       by Akihiko Odaki.
>
>     - Replaced another QSLIST_FOREACH_SAFE with QSLIST_EMPTY+FIRST in
>       the async-fencing patch for more consistency of the code. As was
>       suggested by Akihiko Odaki.
>
>     - Added missing braces around if-statement that was spotted by
>       Alex Bennée.
>
>     - Renamed 'drm=on' option of virtio-gpu-gl device to 
>       'drm_native_context=on' for more clarity as was suggested by 
>       Alex Bennée. Haven't added added new context-type option that 
>       was also proposed by Alex, might do it with a separate patch.
>       This context-type option will duplicate and depecate existing
>       options, but in a longer run likely will be worthwhile adding
>       it.
>
>     - Dropped Linux headers-update patch as headers has been updated
>       in the staging tree.
>
> v3: - Improved EGL presence-check code on X11 systems for the SDL2
>       hint that prefers EGL over GLX by using better ifdefs and checking
>       Xlib presence at a build time to avoid build failure if lib SDL2
>       and system are configured with a disabled X11 support. Also added
>       clarifying comment telling that X11 hint doesn't affect Wayland
>       systems. Suggested by Akihiko Odaki.
>
>     - Corrected strerror(err) that used negative error where it should
>       be positive and vice versa that was caught by Akihiko Odaki. Added
>       clarifying comment for the case where we get positive error code
>       from virglrenderer that differs from other virglrenderer API functions.
>
>     - Improved QSLIST usage by dropping mutex protecting the async fence
>       list and using atomic variant of QSLIST helpers instead. Switched away
>       from using FOREACH helper to improve readability of the code, showing
>       that we don't precess list in unoptimal way. Like was suggested by
>       Akihiko Odaki.
>
>     - Updated patchset base to Venus v18.
>
> v2: - Updated SDL2-dmabuf patch by making use of error_report() and
>       checking presense of X11+EGL in the system before making SDL2
>       to prefer EGL backend over GLX, suggested by Akihiko Odaki.
>
>     - Improved SDL2's dmabuf-presence check that wasn't done properly
>       in v1, where EGL was set up only after first console was fully
>       inited, and thus, SDL's display .has_dmabuf callback didn't work
>       for the first console. Now dmabuf support status is pre-checked
>       before console is registered.
>
>     - Updated commit description of the patch that fixes SDL2's context
>       switching logic with a more detailed explanation of the problem.
>       Suggested by Akihiko Odaki.
>
>     - Corrected rebase typo in the async-fencing patch and switched
>       async-fencing to use a sigle-linked list instead of the double,
>       as was suggested by Akihiko Odaki.
>
>     - Replaced "=true" with "=on" in the DRM native context documentation
>       example and made virtio_gpu_virgl_init() to fail with a error message
>       if DRM context can't be initialized instead of giving a warning
>       message, as was suggested by Akihiko Odaki.
>
>     - Added patchew's dependecy tag to the cover letter as was suggested by
>       Akihiko Odaki.
>
> Dmitry Osipenko (4):
>   ui/sdl2: Restore original context after new context creation
>   virtio-gpu: Handle virgl fence creation errors
>   virtio-gpu: Support asynchronous fencing
>   virtio-gpu: Support DRM native context
>
> Pierre-Eric Pelloux-Prayer (1):
>   ui/sdl2: Implement dpy dmabuf functions
>
>  docs/system/devices/virtio-gpu.rst |  11 ++
>  hw/display/virtio-gpu-gl.c         |   5 +
>  hw/display/virtio-gpu-virgl.c      | 158 ++++++++++++++++++++++++++---
>  hw/display/virtio-gpu.c            |  15 +++
>  include/hw/virtio/virtio-gpu.h     |  16 +++
>  include/ui/sdl2.h                  |   7 ++
>  meson.build                        |   6 +-
>  ui/sdl2-gl.c                       |  67 ++++++++++++
>  ui/sdl2.c                          |  42 ++++++++
>  9 files changed, 309 insertions(+), 18 deletions(-)

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro