[v9] Support virtio-gpu DRM native context

[PATCH v9 00/10] Support virtio-gpu DRM native context

Posted by Dmitry Osipenko 3 weeks, 2 days ago

This patchset adds DRM native context support to VirtIO-GPU on Qemu.

Contarary to Virgl and Venus contexts that mediates 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 DRM native context drivers existing in a wild:

- Freedreno (Qualcomm SoC GPUs), completely upstreamed
- AMDGPU, completely upstreamed
- Intel (i915), merge requests are opened
- Asahi (Apple SoC GPUs), partially merged upstream

# How to try out DRM context:

1. DRM context uses host blobs and on host requires latest 6.13 version
of Linux kernel that contains necessary KVM fixes.

2. Use latest Mesa (both guest and host) and libvirglrenderer versions.
Use build flags documented in tha patch #10 of this series.

3. On guest, use latest Linux kernel v6.14-rc or newer.

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. We will need to optimize hostmem
unmapping that currently happens in a deffered RCU work, blocking
GPU for a substantial time [2].

[2] https://lore.kernel.org/qemu-devel/f58d250d-3831-4ff1-a018-f62f9aeb2527@collabora.com/T/#m17ac72336d28a64c793d4e4e0c87fc7dff9aa847

Changelog:

v9: - Updated doc patch by addresing review comments from Akihiko Odaki.
Made kernel requirements section specific to guest kernel and
removed reference to host requirements. Removed examples of
external projects' build flags.

- Added guest kernel minimum versions to the guest requirements table.

v8: - Addressed review comments from Akihiko Odaki on the doc patch.

- Added r-bs from Akihiko Odaki on the doc patches.

- Extended vrend doc with info about hostmem requirement for GL 4.6

v7: - Added r-b from Alex Bennée to the async fencing patch.

- Updated virtio-gpu doc patch with addressed review comments
from Akihiko Odaki.

v6: - Fixed compilation warning using older version of virglrenderer,
which wasn't fixed properly in v5.

- Added t-bs from Alex Bennée.

- Added patches to improve virgl/venus doc by adding links
to the Mesa doc as was suggested by Akihiko Odaki.

- Updated patch that documents guest/host requirements. Added
links to Asahi nctx and reworked the doc structure by adding
requirements to each context-type section instead of having
one big blob or requirements, which was objected by Akihiko Odaki.

v5: - Added r-bs from Akihiko Odaki.

- Added acks from Michael Tsirkin.

- Fixed compilation warning using older version of virglrenderer that
was reported by Alex Bennée. Noticed that I need to keep old
virgl_write_fence() code around for the older virglrenderer in
"Support asynchronous fencing" patch, so added it back and verified
that old virglrenderer works properly.

- Added new patch from Alex Bennée that adds more virtio-gpu
documentation with a couple corrections and additions to it from me.

- Rebased patches on top of latest staging tree.

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.

Alex Bennée (1):
docs/system: virtio-gpu: Document host/guest requirements

Dmitry Osipenko (8):
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
ui/sdl2: Don't disable scanout when display is refreshed
ui/gtk: Don't disable scanout when display is refreshed
docs/system: virtio-gpu: Add link to Mesa VirGL doc
docs/system: virtio-gpu: Update Venus link

Pierre-Eric Pelloux-Prayer (1):
ui/sdl2: Implement dpy dmabuf functions

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