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VR FPS drop 22.0.1

Hello everyone,

I have experienced a substantial FPS drop when using the latest software version (22.0.1) with respect to the current LTS software version (21.0.10) while using "VR Mode".

For testing purposes I've created two basic models following the same procedure in both of them:

  1. Set default preferences (File -> Global Preferences -> Reset All Preferences).
  2. Show FPS (File -> Global Preferences -> Graphics -> Show FPS Counter).
  3. Create blank model with default Model Units.
  4. Activate "VR Mode".

With the LTS version FPS remains above 100 as can be seen in the following image:

fps-21010.png

But with version 22.0.1 the FPS value moves around 60 (it feels more laggy), which can be a problem especially considering that this model is empty:

fps-2201.png


Do I have to enable some feature that I have forgot about in this new version or is this the expected behaviour ?

___________________________________________________________________

Additional information:

  • Headset: Valve Index
  • About FlexSim:

aboutflexsim.png

___________________________________________________________________


Thanks in advance,

Best regards.

FlexSim 22.0.1
virtual realityfps problem
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fps-21010.png (224.5 KiB)
aboutflexsim.png (698.2 KiB)
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1 Answer

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Phil BoBo answered Paulino SMH edited

It is possible that something that changed between 21.0 and 22.0 is causing the 3D rendering path to be slower on your system now than it was before. It could likely be related to the changes to the manipulation handles or the view frustum culling introduced in FlexSim 21.2.

I tried to replicate the issue on my system, but I was unable to reproduce the problem. I'm getting the same framerate in 21.0 and 22.0 in VR Mode in an empty model and in a large model that is purposefully bottlenecked by the amount of graphics to render (2000 processors in a model). My tests were done with an Oculus Quest headset on an Nvidia Geforce RTX 2080 Ti with an Intel Core i7-4790K CPU though, so it is possible that the bottleneck is happening somewhere on your system that isn't bottlenecked on mine.

It is possible that it is a setting in Steam that's treating different versions of FlexSim differently, but it is more likely a change on the FlexSim side. I need to reproduce the issue though in order to determine what exactly is causing it. Otherwise, it is just blindly guessing. If there are settings in SteamVR, you could try messing with those to determine if maybe it is somehow treating the different FlexSim versions differently, but I doubt it is.

My best guess is that the rendering on your system is CPU-bound and mine is not, and that in 22.0, our graphics pass is requiring more CPU processing than before, so your framerate is decreasing with that increased CPU load, but on my PC, it isn't CPU-bound so I'm not seeing the fps drop between versions. Perhaps my CPU can handle the load in either version and I don't see a fps drop until I add enough stuff to bottleneck the GPU, which is slowing down at the same point in both versions.

I will try to reproduce the issue with a weaker machine on a Vive headset to see if I can reproduce the issue that way.

If anyone else in the community that uses VR could also test the performance of FlexSim 22.0 vs 21.0 and report back their results and their hardware configuration (headset type, CPU info, GPU info), that may be helpful in narrowing down and reproducing this performance issue. I'll see what I can do on my own with the various headsets and hardware in our office though.

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Phil BoBo avatar image Phil BoBo ♦♦ commented ·

Searching around about Valve Index performance issues and settings, I found various references to SS (super sampling) levels and Motion Blurring.

PSA: Try a lower frame rate!!! : ValveIndex (reddit.com)

Performance Valve Index with different SS ratios - Virtual Reality and VR Controllers - IL-2 Sturmovik Forum (il2sturmovik.com)

Based on those pages and the fact that the Valve Index is a 120 Hz headset, it is possible that something in the SteamVR settings is actually causing the difference. It is possible that it is purposefully halving the framerate and kicking on motion smoothing because your system can't keep up with 120 FPS.

I don't have a Valve Index to test with directly right now, but you might be able to try various settings in Steam to see if those make a difference.

If I can't replicate the issue to determine what is happening on the FlexSim side in my tests, then the best course of action may be to get a machine with a better CPU if you can't find settings in SteamVR that are causing or fix the issue.

It seems to me that a Valve Index should be rendering a blank model at 120 FPS regardless of the FlexSim version, and if it isn't, then your system is likely CPU-bound, and you really should be running VR on a better CPU.

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Paulino SMH avatar image Paulino SMH Phil BoBo ♦♦ commented ·

Hi @Phil BoBo and first of all thank you for the quick response,

I did some more tests but I couldn't reach 120fps on any of the two FlexSim versions.

I also run the tests on another PC with better CPU and GPU but I get the same results. However I don't think the PC that I'm currently using is CPU-bound, it can reach 120Hz nicely on other applications, so it must be something directly related to Valve Index and FlexSim. As you can see in the following images the CPU is not heavily loaded:

FlexSim 21.0.10 (~100fps):

21010-resources.png

FlexSim 22.0.1 (~60fps):

2201-resources.png


The FlexSim profile in SteamVR is the same for both versions of the program.

I have even tried with a low-end profile but the problems don't disappear:

steamvr-flexsim-lowprofile.png


The only think that worked was lowering the FPS in SteamVR from 120Hz to 90Hz as you suggested. This way I can reach a stable value of 90 fps as you can see in the following image:

90hz-ok.png


With 90 fps the VR experience is nice and usable but it would be better if we could push our hardware to the limit improving the user experience.

As you pointed out the problem is not directly related with Flexsim version 2022, I have been able to replicate the same problem in FlexSim 2021 Update 2.
With FlexSim 2021 Update 1 I reach over 100 fps so it could be something related to the changes you talked about. Do you think that the features introduced in this version could produce this behaviour? Could FlexSim have a software upper fps limit?

If the answer is yes, could any FlexSim parameter be changed to solve it?


Thank you in advance,

Best regards.

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Phil BoBo avatar image Phil BoBo ♦♦ Paulino SMH commented ·

You have a 6-core CPU. Maxed out single threaded performance is 16.6%.

Based on those screenshots, your framerate in FlexSim is CPU-bound, and FlexSim 22.0 doing more CPU processing per frame than FlexSim 21.0 is probably what is causing your framerate to be lower.

That's good information to know. I'll see what I can do to replicate the issue and see what FlexSim is doing in the draw pass that's taking so much CPU time.

By default, the 3D view only invalidates and repaints when you move it. When VR Mode is enabled and the simulation is not running, the 3D view invalidates itself with a ticker every 8.3 milliseconds for a 120 fps framerate. If you push the Run button so that FlexSim starts processing events and repainting continuously (even in an empty model), then it will repaint as fast as the OS and display will let it, unbounded.

It is possible that something about the ticker isn't keeping up with 120 fps, but it is more likely that each draw pass is taking more than 8.3 milliseconds because of CPU processing.

With changes in the Steam setting, are you getting 90 FPS in version 22.0 or just in version 21.0?

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