https://bugs.kde.org/show_bug.cgi?id=464669
Bug ID: 464669
Summary: Performance issue with Vulkan applications on Wayland
with Intel ANV
Classification: Plasma
Product: kwin
Version: 5.26.5
Platform: Archlinux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
Created attachment 155519
--> https://bugs.kde.org/attachment.cgi?id=155519&action=edit
Hacked together patch that fixes the issue on my end
SUMMARY
Starting with Mesa 22.3 there is a performance issue running Vulkan
applications on KWin on Intel systems with an integrated GPU.
Annoyingly since 22.0 there is a separate bug causing such a performance
regression (https://gitlab.freedesktop.org/mesa/mesa/-/issues/7019), which was
fixed in 22.3, hence only a handful of commits during 22.3 development actually
show expected performance.
I have bisected this on the Mesa side to
https://gitlab.freedesktop.org/mesa/mesa/-/commit/db42ed1e04cc7c9b92fb22cc2eef7f62e73aabba.
This commit introduces a check to verify that the compositor is using the same
GPU as the client, using zwp_linux_dmabuf_feedback_v1::main_device.
On my system KWin reports the major/minor numbers for /dev/dri/card0 (226, 0),
whilst Mesa expects the ones for /dev/dri/renderD128 (226, 128).
Now the fun part is that the wayland protocol documentation has conflicting
information regarding what device should be reported by the compositor, namely
https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/main/unstable/linux-dmabuf/linux-dmabuf-unstable-v1.xml#L484-487
claims this to be unspecified and
https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/main/unstable/linux-dmabuf/feedback.rst#for-compositors
claims it should be set to the rendering device.
So either Mesa should not be comparing the dev_t the way it does or KWin is
reporting the wrong device.
Both Sway (1.8) and Weston (11.0.0) do in fact set the main_device to
/dev/dri/renderD128, unlike KWin, and performance is fine with them.
I have attached a quickly hacked together attempt at fixing this issue in KWin,
by reporting the render device node instead, which does fix the performance
issue and so far has had no ill effects.
If people think this should rather be fixed/changed on the Mesa side (as per
the xml protocol documentation), I can also open up an issue over there
instead.
STEPS TO REPRODUCE
1. Run a Vulkan application, e.g. vkmark.
2. Compare performance on KWin to another compositor, e.g. Weston.
OBSERVED RESULT
Running on Weston it is considerably faster. (vkmark score 5378 <-> 1382)
EXPECTED RESULT
KWin and Weston should have comparable performance.
SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.26.5
KDE Frameworks Version: 5.102.0
Qt Version: 5.15.8
Mesa: 22.3.3
ADDITIONAL INFORMATION
CPU: Intel(R) Core(TM) i7-7500U CPU @ 2.70GHz
GPU: HD Graphics 620 (KBL GT2)
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