Performance issues with Lavapipe in Windows (?)

[George Karpathios]

Hi list, I hope all is well.

I would like to ask if there are any known issues regarding the performance
of Lavapipe in Windows 10.

I'm trying to add support for Vulkan software rendering into a relatively
large 3d modeling/rendering application, so I opted to try Mesa and
Lavapipe. I built LLVM 16.0.0 and Mesa 23.0.1 using the documentation
(thanks for that!). My environment is an 8-core Intel i7 (with an
integrated iGPU) with 32GiB RAM, an nVidia RTX 3070 and Visual Studio
2019/MSVC.

The build procedure seems to be ok (Release builds, proper linking with
either MT or MD runtime libraries, proper DLL loading via VK_ICD_FILENAMES)
but the performance I'm getting during runtime is very slow. It looks like
it needs 1-1.5 seconds to render a virtually empty scene (think just a
floor grid of lines)  and over 15-20 seconds for a frame of a few thousand
vertices. The CPU utilisation also seems to be low, under 20-25%.

I understand that the information I provide is probably vague, but at this
point I just want to rule some probable causes out, like is there any
version of LLVM or Mesa or combination of them that is known to have such
issues? Maybe some build/installation configuration parameter or
environment variable that is important in Windows specifically and I may
have missed (I tried tweaking LP_NUM_THREADS but didn't change anything) ?
Anything that could point me in the right direction is highly valuable &
appreciated.

Also probably worth noting is the fact that the vkcube(pp) demo from the
Vulkan SDK seems to run ok with Lavapipe, but in this case I also notice
(in task manager) a ~50% utilization of the integrated iGPU (why?). In the
aforementioned larger application I don't notice any usage of the
integrated iGPU.

Any advice on what I could check/double check is more than welcome. Thank
you in advance for your time.

Best regards,
George
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