Loader Settings: additional drivers with additional_drivers_use_exclusively=false doesn't allow to run additional drivers as GPU0

[christophe-lunarg]

With device_configurations, we can list devices including additional drivers.

Devices:
========
GPU0:
    apiVersion         = 1.4.305
    driverVersion      = 0.0.1
    vendorID           = 0x10005
    deviceID           = 0x0000
    deviceType         = PHYSICAL_DEVICE_TYPE_CPU
    deviceName         = llvmpipe (LLVM 20.1.6, 256 bits)
    driverID           = DRIVER_ID_MESA_LLVMPIPE
    driverName         = llvmpipe
    driverInfo         = Mesa 25.0.7 (git-35721f1986) (LLVM 20.1.6)
[Vulkan Loader] DEBUG | LAYER:  Unloading layer library C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispig.inf_amd64_02bdcff75475bcf9\.\nvoglv64.dll


    conformanceVersion = 1.3.1.1
    deviceUUID         = 6d657361-3235-2e30-2e37-000000000000
    driverUUID         = 6c6c766d-7069-7065-5555-494400000000
GPU1:
    apiVersion         = 1.3.271
    driverVersion      = 101.5186
    vendorID           = 0x8086
    deviceID           = 0x56a1
    deviceType         = PHYSICAL_DEVICE_TYPE_DISCRETE_GPU
    deviceName         = Intel(R) Arc(TM) A750 Graphics
    driverID           = DRIVER_ID_INTEL_PROPRIETARY_WINDOWS
    driverName         = Intel Corporation
    driverInfo         = Intel driver
    conformanceVersion = 1.3.6.3
    deviceUUID         = 8680a156-0800-0000-0e00-000000000000
    driverUUID         = 33312e30-2e31-3031-2e35-313836000000
GPU2:
    apiVersion         = 1.3.295
    driverVersion      = 553.22.0.0
    vendorID           = 0x10de
    deviceID           = 0x2208
    deviceType         = PHYSICAL_DEVICE_TYPE_DISCRETE_GPU
    deviceName         = NVIDIA GeForce RTX 3080 Ti
    driverID           = DRIVER_ID_NVIDIA_PROPRIETARY
    driverName         = NVIDIA
    driverInfo         = 553.22
    conformanceVersion = 1.3.8.2
    deviceUUID         = bc4a01b1-5641-8058-47a8-151a395a80c7
    driverUUID         = 1a8cb5ae-3ba9-590a-8ba4-a405828f4748

However, when putting the additional drivers first, as "GPU0", running vkcube shows the the GPU1 is used instead.

When moving a "typically" drivers first, then this typically drivers is used. In my case, this typical driver could be either my Nvidia or Intel GPU.

[charles-lunarg]

I think this is actually a consequence of KhronosGroup/Vulkan-Tools#1047 which changes vkcube's gpu selection logic from "the first in the list" to "discrete, then integrated, then virtual, then CPU".

I am open to removing that logic from vkcube but that should be moved to Vulkan-Tools

[charles-lunarg]

@christophe-lunarg Can you specify which vkcube you used? IE which SDK version, that would rule out the problem where vkcube changed its logic.

[christophe-lunarg]

Ah that could be! Rather than removing this logic, what about adding an argument to control that behavior?

I'll test tomorrow with an old version of vkcube!

[christophe-lunarg]

Using this file, with vkcube from SDK 1.4.304.1, I can still reproduce the issue:
vk_loader_settings.json

Selected GPU 0: NVIDIA GeForce RTX 3080 Ti, type: DiscreteGpu

But maybe, I agreed it might not be a Loader issue but a vkcube issue that play around with device selection... this said, how does it manage to see my NVIDIA GPU when device_configurations only list llvmpipe? So it sounds like something is of with the loader too.

Running vulkaninfo, I am getting:

Devices:
========
GPU0:
	apiVersion         = 1.4.305
	driverVersion      = 0.0.1
	vendorID           = 0x10005
	deviceID           = 0x0000
	deviceType         = PHYSICAL_DEVICE_TYPE_CPU
	deviceName         = llvmpipe (LLVM 20.1.6, 256 bits)
	driverID           = DRIVER_ID_MESA_LLVMPIPE
	driverName         = llvmpipe
	driverInfo         = Mesa 25.0.7 (git-35721f1986) (LLVM 20.1.6)
	conformanceVersion = 1.3.1.1
	deviceUUID         = 6d657361-3235-2e30-2e37-000000000000
	driverUUID         = 6c6c766d-7069-7065-5555-494400000000

On my side, I'll investigate how vkcube is working with device selection, maybe adding an argument to control or not the device selection.

[christophe-lunarg]

If I use vkcube --gpu_number 0, even with the SDK 321, then I can run lavapipe. So there is definetly something going on with the GPU selection in vkcube things too.

It looks like the default behavior of vkcube is vkcube --gpu_number -1 which cause automatic selection. Because of the context of the SDK and this loader change, I think we could consider vkcube --gpu_number 0 to be the default, so changing vkcube. What would you think about such change?

This said, if we can understand how vkcube manage to see physical devices not listed in device_configurations, it would likely make this change of default vkcube behavior pointless.

I'll continue debugging vkcube to figure this out...

[christophe-lunarg]

Okkkkkk, something is terrible weird, now, I no longer reproduce the issue, I am getting vkcube to start with llvmpipe in vkconfig with the same vk_loader_settings.json than above. Oo