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Dramatic drop in fps with UE4.26 + SteamVR

After years of creating VR projects with UE4, we’re running into very low frame rates with a fresh project using 4.26.

Testing hardware includes machines with 1080Ti and 2080, Cosmos and Cosmos Pro headsets. Normally we’d get at least fps in the 70-80 range in VR before a build. Currently we’re seeing 5 - 20, upwards to 30-40 with an essentially empty map.

Map includes a path with camera, some landscape (without landscape fps is low 30s-40s). Default sky sphere (which seems make a 10-15 frame drop too), and some static meshes with minimal affect of fps.

I did a quick test between 4.24, 4.25, and 4.26 using Epic’s advanced race car project. Essentially the same project created in each of the UE4 engine versions. Both 4.24 and 4.25 show 70-80 fps in VR. But with 4.26, fps drops to about 40. Also there seems to be some issues with StreamVR having to restart whenever a 4.26 project is launched.

We’re curious if anyone else is having similar issues, and if so, if you have pin pointed the cause of the issues. Thanks for any help and info!

There’ve been multiple scattered reports of 4.26 causing a drop in performance. One of them was related to showflag.transparency I believe but that was not VR specific, could give it a try though by setting that to 0. I do feel like its been hard keeping performance up in VR on 4.26 and it feels like there’s so much overhead now that its hard to do anything, definitely interested in a follow-up if you do discover something!

Also might be worth submitting a detailed bug report with your comparison between the different versions of UE. It would really be nice if someone from Epic could look into this.

Have you profiled the application to see what is eating up the performance? Is it GPU or CPU bound?

Also note that VR runtimes will throttle the application down to fractions of the framerate when it fails to meet the target, so measuring the frame time in ms is much more useful than measuring FPS. If your application fails to meet 80 FPS it will show 40 regardless of the actual performance.

I have an constant issue with the render thread blocking and breaking frame sync when using 4.26 with the SteamVR plugin, and I’m wondering if it would be the same thing causing it.