It actually depends on several factors. Surprisingly, games that are heavily CPU bottlenecked often run better on Linux under Proton than the native Windows version.
That being said, for games that are GPU bound, a 20% deficit on a Nvidia GPU is actually about what I'd expect.
and yeah, 5-15% seems "normal" but 20% is pretty reasonable considering all the other factors involved. But I would be concerned.
I would say to do the following:
make sure shaders have fully precached. Steam supports this in the background which makes me wonder if it is always finished if i start a game after an update
Check a few other games and especially engines. So Unreal, Unity, a few proprietary, etc
Look into using mangohud and other monitoring tools to try to see WHAT is different. Memory usage, draw time, etc.
I was seeing 30-40% performance loss in BG3 and the stutters were too frequent to play Apex Legends. After that I gave up on gaming on Linux. If I’m doing any dev work I use my Linux partition, but day to day I drive windows for gaming.
Were you using the Vulkan renderer after Patch 2? There's a massive performance regression that got introduced with that Patch. DX11 still works fine tho.
the stutters were too frequent to play Apex Legends
This should be fixed after graphics pipeline library support was added to both Nvidia and AMD. If you tried it before that, it was indeed a stuttery mess. It is dramatically better now.
I actually got better performance in BG3 with my Arch system compared to Windows. The game crashes to desktop every 10 minutes in windows and runs relatively stable in Linux.
Ironically, I actually got better performance in Fedora than Win11, same machine, playing Monster Hunter World. I think in my case it was because of the background stuff running in Windows. I run Linux pretty bare.
I'm running AMD, not Nvidia, but I didnt notice much of any performance loss in the games I played during the brief time I had both Linux and Windows installed, before migrating fully to linux.
On games that worked well, at least. There was a couple games that didnt play great with proton at the time, that have long since been sorted out and run great.
hell, iirc, a couple games even ran better on linux.