[libplacebo] Couldn't setting "vulkan-device" disable physical devices enumeration?

[szpak]

I have a laptop with Intel + NVidia cards and in a "work configuration", I use nouveau to keep the NVidia card disabled. After upgrade to Fedora 42, with Vulkan enabled globally by default, mpv (and many other apps) started using my NVidia card by default. I was able to manage it somehow with VK_ICD_FILENAMES, but for mpv, I just speficy vulkan-device=....

It works, but... the devices are still enumerated, which makes my NVidia card switch from DynOff → DynPwr, which in turn (as I suspect) causes ~2s delay on mpv initialization.

Couldn't vulkan-device=... completely disable physical devices enumeration (and maybe fallback to it once the given device is not found)?

Some logs:

[   0.001][v][cplayer] mpv v0.40.0 Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
[   0.001][v][cplayer] libplacebo version: v7.349.0
[   0.001][v][cplayer] FFmpeg version: 7.1.1 (runtime 7.1.2)
[   0.001][v][cplayer] FFmpeg library versions:
[   0.001][v][cplayer]    libavcodec      61.19.101
[   0.001][v][cplayer]    libavdevice     61.3.100
[   0.001][v][cplayer]    libavfilter     10.4.100
[   0.001][v][cplayer]    libavformat     61.7.100
[   0.001][v][cplayer]    libavutil       59.39.100
[   0.001][v][cplayer]    libswresample   5.3.100
[   0.001][v][cplayer]    libswscale      8.3.100
[   0.001][v][cplayer] Configuration: -Dalsa=enabled -Dbuild-date=false -Dcaca=enabled -Dcdda=enabled -Dcplayer=true -Dcplugins=enabled -Dcuda-hwaccel=enabled -Dcuda-interop=enabled -Ddmabuf-wayland=enabled -Ddrm=enabled -Ddvbin=enabled -Ddvdnav=enabled -Degl-drm=enabled -Degl-wayland=enabled -Degl-x11=enabled -Degl=enabled -Dgbm=enabled -Dgl-x11=enabled -Dgl=enabled -Dhtml-build=enabled -Diconv=enabled -Djack=enabled -Djavascript=enabled -Djpeg=enabled -Dlcms2=enabled -Dlibarchive=enabled -Dlibavdevice=enabled -Dlibbluray=enabled -Dlibmpv=true -Dlua=enabled -Dmanpage-build=enabled -Dopenal=enabled -Dopensles=disabled -Doss-audio=disabled -Dpipewire=enabled -Dplain-gl=enabled -Dpulse=enabled -Drubberband=enabled -Dsdl2-audio=enabled -Dsdl2-gamepad=enabled -Dsdl2-video=enabled -Dsdl2=enabled -Dshaderc=disabled -Dsndio=disabled -Dspirv-cross=disabled -Duchardet=enabled -Dvaapi-drm=enabled -Dvaapi-wayland=enabled -Dvaapi-x11=enabled -Dvaapi=enabled -Dvapoursynth=enabled -Dvdpau-gl-x11=enabled -Dvdpau=enabled -Dvector=enabled -Dvulkan=enabled -Dwayland=enabled -Dwerror=false -Dx11=enabled -Dxv=enabled -Dzimg=enabled -Dzlib=enabled -Dprefix=/usr -Dbindir=/usr/bin -Ddatadir=/usr/share -Dincludedir=/usr/include -Dinfodir=/usr/share/info -Dlibdir=/usr/lib64 -Dlibexecdir=/usr/libexec -Dlocaledir=/usr/share/locale -Dlocalstatedir=/var -Dmandir=/usr/share/man -Dsbindir=/usr/bin -Dsharedstatedir=/var/lib -Dsysconfdir=/etc -Dauto_features=auto -Dbuildtype=plain -Dwrap_mode=nodownload
[   0.001][v][cplayer] List of enabled features: alsa caca cdda cplugins cuda-hwaccel cuda-interop dmabuf-interop-gl dmabuf-wayland drm dvbin dvdnav egl egl-drm egl-wayland egl-x11 ffmpeg ffnvcodec gbm gl gl-x11 glibc-thread-name glob glob-posix gpl iconv jack javascript jpeg lcms2 libarchive libass libavdevice libbluray libdl libplacebo linux-fstatfs lua-5.1 memfd-create memrchr openal pipewire posix posix-shm ppoll pthread-condattr-setclock pulse rubberband rubberband-3 sdl2 sdl2-audio sdl2-gamepad sdl2-video uchardet vaapi vaapi-drm vaapi-wayland vaapi-x11 vapoursynth vdpau vdpau-gl-x11 vector vk-khr-display vt.h vulkan wayland wayland-protocols-1-32 wayland-protocols-1-38 wayland-protocols-1-39 wayland-protocols-1-41 x11 xv zimg zimg-st428 zlib
...
[   0.001][d][file] resize stream to 131072 bytes, drop 0 bytes
[   0.001][d][file] Stream opened successfully.
[   0.002][v][libplacebo] Initialized libplacebo v7.349.0 (API v349)
[   0.002][d][libplacebo] Available instance version: 1.4.313
[   0.002][d][libplacebo] Spent 0.242 ms enumerating instance layers
[   0.002][d][libplacebo] Available layers:
[   0.002][d][libplacebo]     VK_LAYER_MESA_device_select (v1.4.303)
[   0.066][v][libplacebo] Spent 63.724 ms enumerating instance extensions
[   0.066][d][libplacebo] Available instance extensions:
[   0.066][d][libplacebo]     VK_KHR_device_group_creation
...
[   0.066][v][libplacebo]     VK_KHR_portability_enumeration
[   0.072][d][libplacebo] Spent 6.373 ms creating vulkan instance
[   2.101][v][cplayer] Applying profile 'default'...                                    <---- 2s later!
[   2.101][v][cplayer] Setting option 'hwdec' = '' (flags = 4)
[   2.101][v][cplayer] Setting option 'sub-codepage' = 'cp1250' (flags = 4)
[   2.101][v][cplayer] Setting option 'vulkan-device' = 'xxx' (flags = 4)
[   2.101][v][libplacebo] Initialized libplacebo v7.349.0 (API v349)
[   2.101][d][libplacebo] Available instance version: 1.4.313
[   2.101][d][libplacebo] Spent 0.220 ms enumerating instance layers
...
[   2.318][v][vo/gpu/libplacebo] Spent 53.981 ms enumerating physical devices
[   2.318][v][vo/gpu/libplacebo]     GPU 0: NVIDIA GeForce GTX 1660 Ti (NVK TU116) v1.4.311 (discrete)
[   2.318][v][vo/gpu/libplacebo]            uuid: xxx
[   2.319][d][vo/gpu/libplacebo]      -> excluding due to UUID mismatch
[   2.319][v][vo/gpu/libplacebo]     GPU 1: Intel(R) UHD Graphics 630 (CFL GT2) v1.4.311 (integrated)
[   2.319][v][vo/gpu/libplacebo]            uuid: xxx
[   2.319][v][vo/gpu/libplacebo]     GPU 2: llvmpipe (LLVM 20.1.8, 256 bits) v1.4.311 (software)
[   2.319][v][vo/gpu/libplacebo]            uuid: xxx
[   2.320][d][vo/gpu/libplacebo]      -> excluding due to UUID mismatch
[   2.320][v][vo/gpu/libplacebo] Vulkan device properties:
[   2.320][v][vo/gpu/libplacebo]     Device Name: Intel(R) UHD Graphics 630 (CFL GT2)
[   2.320][v][vo/gpu/libplacebo]     Device ID: 8086:3e9b
[   2.320][v][vo/gpu/libplacebo]     Device UUID: xxx
[   2.320][v][vo/gpu/libplacebo]     Driver version: 6401009
[   2.320][v][vo/gpu/libplacebo]     API version: 1.4.311

[kasper93]

No, it's not possible.

Vulkan gives vkEnumeratePhysicalDevices API that returns list of opaque handles (VkPhysicalDevice) for each device. We then query properties of each device for selection, based on name or type of gpu and so on. Next we this handle to create Vulkan context and what not. There is no way to get a VkPhysicalDevice "directly", as it's application job to select it.

Long story short, this is a driver / kernel bug where they should not wake up the device for sole purpose of enumerating them.

It's known issue, you can read related discussion here (it not only affects NVIDIA...):
#16218
https://gitlab.freedesktop.org/drm/amd/-/issues/2295
https://gitlab.freedesktop.org/mesa/mesa/-/issues/11383

Some duplicates:
https://gitlab.freedesktop.org/mesa/mesa/-/issues/12972
https://gitlab.freedesktop.org/mesa/mesa/-/issues/13001

[szpak]

Thank you for your explanations. I will comment/subscribe to those issues.