Question about viogpu profiling capabilities

[sharkautarch]

It seems like there is a tracing.h file for WPP tracing in viogpudo.
Is WPP tracing locked behind a build-time config, or is it possible to enable it at runtime?
Lastly, do you have any other advice for how to best profile the viogpu driver & services?
For context, I've been experimenting with using virtio-gpu-pci w/ nvidia gpu passthru, and there appears to be some performance degradation w.r.t. viogpu that is not necessarily due to being bound by memory bandwidth limitations.

Reason why I know it isn't a memory bandwith problem is because I've been setting the guest display's resolution to 1280x800 or smaller (upscaled on the host to 1920x1200 using gamescope.) And testing w/ running heaven benchmark shows that I'm able to, on the host side, get 99-100fps.

However, outside of that, (including w/ testing running testufo on firefox and playing a game that I don't think uses fullscreen exclusive mode called ss13) I seem to be getting 50-60fps, and even sometimes 30-40fps (seems to suddenly switch between 50+fps and 30-40fps every few minutes or so)

And on firefox testufo, disabling dwm using a special tool seems to bring the fps back up to around 60fps:

Oddly enough, disabling dwm doesn't seem to help w/ fps as much for ss13

Reason why I'm posting a discussion and not an issue about this fps stuff is because I want to first check if somehow the recently-merged PR #1128 changes any of this

[YanVugenfirer]

Hello @sharkautarch ,

Are you testing the experimental PR #943, or just a regular driver?
A regular virtio-gpu driver in Windows doesn't support acceleration, so it is not expected to have any performance comparable to the actual physical GPU.

[sharkautarch]

@YanVugenfirer
I'm testing using nvidia gpu passthrough and virtio-gpu-pci on the same vm, where basically the nvidia-gpu does the rendering, and virtio-gpu-pci forwards the rendered stuff to the host.

Are you testing the experimental PR #943, or just a regular driver?

using the regular driver btw

Reason for why I'm using this setup is that I'm on a hybrid muxless laptop, and although the intel igpu hardware supports sr-iov, I'm still waiting for sr-iov support in the kernel w/ the Xe driver to mature.
I can tell that the nvidia-gpu in this setup is indeed increasing fps since w/o the nvidia gpu driver installed, the vm is stuck at less than 40fps, whereas with the nvidia gpu driver installed, it can technically go all the way to 100fps from the host perspective (via mangoapp HUD measuring frame times on the actual host machine) when running heaven benchmark in the vm (and heaven benchmark reports higher fps at around 300fps, tho ofc the fps drops down to 100fps due to bandwidth limitations.)

[YanVugenfirer]

OK. But what kind of virtio-gpu driver are you using?

[sharkautarch]

OK. But what kind of virtio-gpu driver are you using?

I believe I'm using the viogpudo driver

If you're asking what version, it's the one from: https://fedorapeople.org/groups/virt/virtio-win/direct-downloads/virtio-win-pkg-scripts-input/latest-build/virtio-win-prewhql-0.1.zip

[YanVugenfirer]

Then, it is expected to have diminished performance compared to pass-through.

[sharkautarch]

Yes, but it seems like there's some level of performance degradation that isn't due to bandwidth limitations because again:

• I'm able to get 100fps when running heaven benchmark
• I forgot to mention this, but I also was able to get ~120fps when running a linux vm (an old gparted live cd of all things) with the same libvirt/qemu config
  
• the windows desktop sometimes is able to run at 50-60 fps, where it remains like that for a while, but then will randomly go down to ~40fps, and then again after some time will go back up to 50-60fps and so on...
• Disabling dwm seems to bring the fps back to 60fps on firefox, no longer going below 50fps for as long as dwm is disabled, tho it doesn't seem to help as much for other programs/apps

I know that there is a certain amount of performance degradation that is unavoidable w/ this setup, but I just want to figure out how best to profile the system & driver to find anything where performance can be improved somewhat

I'm open to compiling the driver myself, if needed, to get better profiling details

[YanVugenfirer]

xperf can be used to profile where OS spends its time: https://learn.microsoft.com/en-us/windows-hardware/test/wpt/windows-performance-toolkit-technical-reference

[sharkautarch]

@YanVugenfirer
I'm aware of xperf, wpr and wpa
Is it possible to enable WPP tracing for viogpudo without recompiling?

[vrozenfe]

WPP works in general.

But in the current version it is not possible to adjust the verbosity level. It is all or nothing. I will fry to fix it in the next public build

[vrozenfe]

For the testing purpose only you can try to activate
"UsePhysicalMemory" and "UsePresentProgress" flags (they are disabled in the downstream build)
https://github.com/virtio-win/kvm-guest-drivers-windows/blob/master/viogpu/viogpudo/viogpudo.inx#L72C7-L72C24