I’ve been doing a lot of profiling to try and get to the bottom of this, but I’m pretty much out of ideas.
Ever since I upgraded my VR project from 2021.1.X to 2021.2.X, I’ve been struggling with 1.5X higher frame times.
Below are direct comparisons of the exact same project running in their respective versions.
On the left is 2021.1.25f1
On the right is 2021.2.16f1
And here it is running in 2021.3.0f1.
Same exact file; upgraded directly from 2021.1.25f1
It won’t even run at 90hz, whereas it will run at 144hz with plenty of headroom in 2021.1
Just to be clear, I’m on 2021.3 LTS now. Not 2021.2. You should probably upgrade to 2021.3 LTS as well. There’s no reason to stay on a tech release.
I haven’t been able to find anyone else out there complaining of performance issues in OpenXR + 2021.3. Mine seems to be some kind of weird edge-case. I’m pretty sure it’s an OpenXR 1.3.1 issue. When I upgraded from 2021.1, OpenXR updated to 1.3.1 and that’s when the problem started.
Are you experiencing performance issues? Or are you just curious if there are performance issues with it in general?
We’re on 2021.2.19f1, for some very specific bugfixes we were hitting that were pretty severe. We haven’t downgraded and run an exact side by side comparison of the performance, but if you have a solid repro it would be nice to have it confirmed by someone on Unity’s side - so we can at least track what versions it likely exists in.
We are always up against the performance wall so any savings from bugfixes like this are life saving. If Unity doesn’t look into it I suppose we will run a comparison in our next optimizing phase and see.
Unfortunately, it’s basically impossible for me to issue a reliable repro. The bug is very hard to pin down, and only affects certain machines at the office. I’m pretty sure it has something to do with OpenXR 1.3.1, but I can’t be sure. This “performance wall” I’m up against isn’t a minor optimization - we’re talking like a 3x slowdown in frame times in a side-by-side comparison - it’s very broken.
I’ve isolated the issue:
It presents itself when using URP + Forward Renderer + SSAO Render Feature in OpenXR projects for VR in anything after 2021.1.X.
The SSAO render feature tanks the FPS by a factor of 2-3 and produces all sorts of wild swings in frame timing. The Profiler doesn’t pick up on the FPS problems and only presents itself in the SteamVR runtime.
