Intermittent Frame Rate Drop

[Gyster]

I'm brand new to DCS and I've been trying to get my graphics settings dialed in and I can't seem to find a solution to what I'm experiencing.  I'm using a Pimax 8KX. My PC specs are i9-13900k running at 5.6 GHz, Asus RTX 4090 TUF OC, 64 GB 6000 MHz ram.  Using a Virpil T-50 CM3, VKB Gunfighter Pro with twist.

I have Pimax softare set at 75 Hz, no upscaling, using lighthouse, FOV large, Render Quality balanced, Fixed Foveated Rendering Off, Panel Projection Compatibility Mode checked, Smart Smoothing checked, Hidden Area Mask checked.

I turned off HAGS.

I set Nvidia 3D graphics settings per these screenshots.

I'm running MT version of DCS, PimaxXR, OpenXR Toolkit, Open Composite, XRNeckSafer, and MSI Afterburner.

I would post screen shot of DCS settings but I think I would need to disconnect the 8KX to grab a shot of that from the monitor.

I've been testing using instant action 1 v 1, 2 v 1, and Low Level Hell.  FPS holds at right about 75 for quite awhile but then, the screen flickers and FPS will suddenly dip to about 38, then 45 and right back to 75 within about 5 to 10 seconds or so.  It seems to do this more often when I'm very close to the ground and flying through cityscapes, but will also do it when I'm at altitude - often during a merge.

Since I can't see the Afterburner overlay in the headset, I've been lifting it when this happens to see if there's a big load on GPU or CPU.  Neither seems to be overly stressed - GPU around 70% and CPU about 40%.

Anyone care to try and help me troubleshoot this?

[hsth]

Maybe try Mastiff's settings? 

 

[Gyster]

It seems to have made it happen more frequently. Even just in menus it will drop and in Low Level Hell, it is pretty bad.  :o(  The system should be quite capable, so I'm just missing something.  Thank you again for taking time to reply.

[average_pilot]

Change affinity for DCS.exe to exclude the core 0 and see if it helps.

[edmuss]

Only hypothethesizing here as I'm not familiar with the pimax software....

Smart smoothing is reprojection, therefore if you fail to hit your refresh rate of 75Hz it will hack the FPS down to half (37/38) and then once your GPU has the frametimes below refresh rate of 13.3ms it will disable the reprojection and FPS will rise back up to 75 again.  The cause of the framerate drop could be CPU or GPU, have the DCS performance overlay enabled and look to see what spikes occur in the lower charts.

I suspect that you're only just beating refresh rate + the overhead for running the reprojection so when the scene gets more complicated (low level or in the merge) it's dipping the framerate (74fps will be enough) and triggering reprojection.  Try turning smoothing off and see if it still happens, if you drop below refresh you may start to see ghosting/double image of fast moving objects, particularly when looking sideways.

Edited January 17, 2024 by edmuss

[Gyster]

Thank you guys for taking time to try and help - I'm running out of ideas and getting overwhelmed trying to learn about OpenXR, PimaxXR, OpenComposite, OpenXR Toolkit, what all these settings mean, and so on.  I've been reading a thread about the mt version of dcs and placed that file, but haven't noticed any change.

I've seen some references to parking cpu cores too.  I think that's where I ran across the term affinity (for DCS).  I don't recall seeing how to change that though, but I think I can find it. Would that interfere with or affect parking cores?

I think you're on the right track with the reprojection thoughts edmuss.  When I turned that off though, the stuttering was really bad so I quickly gave up on that notion before trying to tweak settings with it turned off.  From what I've seen, many are running DCS in VR with less robust equipment so I wouldn't think I would need it...there's not much faster hardware available - 14th Gen CPUs offer a bit more performance, but from what I've seen it's not much.  It kinda sounds like I'm bragging but that's definitely not what I'm getting at - this hardware will be long in the tooth in no time.  I'm trying to support the notion that reprojection shouldn't be needed with my setup.  From what I understand, it creates frames that are "close" to what is actually being rendered an interleaves these frames into the video stream.  So...ghosting and double images (which is what I'm getting) are a result.  This is when I'm not seeing frame rate drops.  Just thought, the texture on my plane and the cockpit look great!

Anyway, thank you guys - you don't have to spend your time to help out and I really appreciate that you do.  I'll keep reading, watching videos and hopefully get this thing working satisfactorily.

Oh yeah, how do I enable the performance overlay?  I'm only displaying FPS and I think that was through OpenXR Toolkit.  And do you know where I can learn how to navigate the ingame menus?  That might be a major pain in the butt in VR.

 

 

 

Edited January 18, 2024 by Gyster

[edmuss]

The problem isn't so much the hardware but a limitiation of the DX11 DCS engine when it comes to very high resolution; it's just not as efficient as modern engines - the upcoming vulkan engine upgrade should hopefully alleviate the issue.

If you consider the resolution that the 8KX is running at, a brief google seems to indidicate that 5024x3160 per eye is the render target.  You may be running less than this but to put it into perspective, this gives a render pixel count of almost 32mp which is equivalent to 3.8 * 4k monitors.  You're simply asking too much of the GPU to be able to run DCS >75fps constantly at that resolution.  For reference, the reverb G2 at 100% needs 19.5mp and the varjo aero at 35ppd (default high resolution setting in varjo base) needs 7mp due to the way that the eye tracking  DFR (Dynamic Foveated Rendering) works.

Have a look at using QVFR by mbucchia to give you some of the performance gains of DFR despite you not having an eye tracking headset, it will simply revert to a fixed foveated rendering but you may be able to see the lower resolution peripheral area depending on the lenses and how you set it up.

You don't need open composite, that is a very old and now deprecated method of running DCS via openxr, you should be using openxr natively via the MT preview beta.

The DCS performance overlay is right ctrl + pause, however the openxr toolkit overlay will give you more information, particularly with the advanced level of detail.  Keep an eye on appGPU frametime value, your ultimate aim is to keep it below the refresh rate, if you can do this then it should all be smooth.

Frametime = 1000/fps so for 75Hz refresh rate your frametime target is 13.3ms, if your appGPU frametime is above 13.3ms then you have missed the refresh rate and you will experience stuttering and/or trigger reprojection. 

All of the information you need about openxr toolkit is fully documented on the website https://mbucchia.github.io/OpenXR-Toolkit/

[Gyster]

Wow, thank you edmuss.  It seems like you said, the 8kx can benefit from FR even if it's not dynamic because of the lack of eye-tracker.  (I can't wait to try this)  Also, thank you for the information on OpenXR Toolkit and the overlays and for giving my target frametime.  I had to come home from work to repair our water heater (I don't want to take cold showers but moreover I don't want to hear my wife's opinion on taking cold showers) That's done (replace thermocouple) so now I'm off to experiment with this.  I'll circle back with feedback and hopefully not have a bunch more questions to bug you with.  Many many thanks!

[Gyster]

Hi edmuss, that made a huge difference in appearance - being able to turn off reprojection (smart smoothing in Pimax) makes everything look much better.  In the Pimax software, I set foveated rendering on minimum.  The frame rate still dips pretty frequently, but I'm not seeing appGPU above .3 ms.  I did see the one above that reach 3.4 ms once, but neither of these are getting very high.  Most of the time appGPU is showing 0 ms.  I'm running pretty high settings in DCS and turned off DLSS.  I only tested in 2 v 1 in the Caucuses.  I'm not seeing any stutter while in the settings menu and the framerate is solid 75 there.  I read some people using the mt version are getting the stuttering in menus, but I'm not clear on whether this is the settings menu or when you access menus while flying (I haven't learned how to do that yet).  So, with these low frametime values, I'm not sure what could be causing the stuttering.  All the same, your advice has helped tremendously, and I really appreciate that you took the time to reply!  I'll keep tweaking and reading and hopefully get this all worked out.  I'm much more enthusiastic today than I was yesterday though...thank you.

[edmuss]

Are you sure that you're reading appGPU and not appCPU? 3.4ms is 295 fps which no GPU is going to achieve in DCS VR

When checking frametimes for performance, it's worthwhile disabling turbo mode in openxr toolkit as this will give spurious CPU values.

Glad it's running a little better now though!

[Gyster]

Definitely reading appGPU...I did have turbo mode on so I'll go back and test and get the depressing real numbers   Definitely going in the right direction.  I was completely out of ideas, and the information you provided has been really helpful.  I can't say thank you enough!

[Gyster]

Hi edmuss, that made a huge difference in appearance - being able to turn off reprojection (smart smoothing in Pimax) makes everything look much better.  In the Pimax software, I set foveated rendering on minimum.  The frame rate still dips pretty frequently, but I'm not seeing appGPU above .3 ms.  I did see the one above that reach 3.4 ms once, but neither of these are getting very high.  Most of the time appGPU is showing 0 ms.  I'm running pretty high settings in DCS and turned off DLSS.  I only tested in 2 v 1 in the Caucuses.  I'm not seeing any stutter while in the settings menu and the framerate is solid 75 there.  I read some people using the mt version are getting the stuttering in menus, but I'm not clear on whether this is the settings menu or when you access menus while flying (I haven't learned how to do that yet).  So, with these low frametime values, I'm not sure what could be causing the stuttering.  All the same, your advice has helped tremendously, and I really appreciate that you took the time to reply!  I'll keep tweaking and reading and hopefully get this all worked out.  I'm much more enthusiastic today than I was yesterday though...thank you.

For some reason the earlier message didn't post until now...maybe I didn't hit the submit button.  Anyway, I turned off turbo mode and that didn't seem to impact the values in the overlay, they're still incredibly optimistic.  However, in the one session I tested in, I got no stutter and no framerate drop at all.  I recall reading somewhere to turn off turbo mode if it caused stutter, and that seems to have been largely the problem here.  I think I try disabling foveated rendering and see what happens.  Maybe even turn refresh rate up to 90hz.  Thanks edmuss, I don't know how long it would have taken to figure this out without your help.

[Gyster]

I changed the settings in Pimax to FOV: Normal, Render Quality Maximum, FFR Off, Parallel Projection, Smart Smoothing, Hidden Area Mask, and Compatible with Vive all unchecked. I tried turning off Quadviews and that produced appGPU from 12-14ms and significant stutter but framerate never dropped below 60 or so.  I turned it back on and no stutter and solid 75 fps in 2v1 instant action.  Same settings in low level hell produced stuttering, but not as bad (micro-stutter maybe?) but appGPU never got above .3 ms and framerate stayed in the 70s for the most part.  I haven't figured out how to take a screenshot or record video with headset or I would post my in game settings, and try to make a video to illustrate what I'm talking about.

[Bojanglez]

Hey. Happy I came across this!

I have a very similar Setup as you do.

4090. i-9. 8KX…

your issue seems to be exactly what I am seeing. Maybe you can confirm:

I fly and see 91 FPS and down to min 60FPS. Then out of nowhere I have a short phase of maybe 30 sec where frames drop to 1FPS or even full freeze for a bit. Even when I hit ESC to pause. Then after a while it just recovers and goes back to 90FPS. Like a hiccup in my PC. I keep flying and it keeps happening. Seems like when I restart DCS it resolves itself. It seems random. Some days I fly with no issues at all. But if it happens it keeps happening. Very annoying. 
 

does that seem familiar?

 

Edit: yap. Sometimes it happens in main menue and doesn’t seem related to what’s happening in DCS in that moment. 

Edited February 9, 2024 by Bojanglez

[Gyster]

7 hours ago, Bojanglez said:

Hey Bojanglez, it is similar and different.  I have Pimax set at 75 mhz so I cap out at about 76 fps.  The symptoms I was experiencing were more persistent though.  I've done quite a bit of tweaking and yesterday I installed Bitsum ParkControl and it seems to have made a pretty big difference.  I've been in SP and MP and flying low for testing and it seems to stay at 70+ fps but it still looks a little choppy when looking towards 3 or 9 o'clock...the framerate doesn't drop though.  I'm such a noob here, I am totally clueless in the MP servers - I spend my time flying around and trying to figure out where I am on the map.  I did shoot down a couple guys in Hornets the other day though lol.  (I only have the 109).  Well, I shot down one and nicked the other guy and he ran back to his base.  I might try uping the refresh rate to 90 and see what happens.  I don't know how to do screen grabs in the headset, or I'd post my settings.  I am running PimaxXR, XRTookit, and Quadview.  If you don't mind, I wouldn't mind knowing how you have everything set and I will certainly post what I have if I can figure out how to do screenshots in the headset.