How important is VRAM to VR?

[obious]

Hi All,

I have a 3080ti and am running my Reverb G1 at 90fps with my DCS settings toned down accordingly to help reach 90Hz.

Now that GPU prices are *somewhat* declining, I’m thinking about upgrading and am wondering if the amount of VRAM that a GPU has matters for VR? When looking at the 3090ti (and even the 40XX cards that are around the corner) that has 24gb VRAM vs. the 12gb of the 3080ti series, does that make much of a difference for VR at all?

I’m currently getting about 7ms when flying the Hornet in PG but when I land on an empty Stennis, my FPS tanks for ~75fps and GPU frame time spikes. I wonder if that’s because ED recently applied the Super Carriers textures to the Stennis?

Thanks 

[unlikely_spider]

My understanding is that it does make a big difference. I don't have any objective A/B tests handy though.

[Brainfreeze]

1st you do not need 90fps to be smooth and fluid.  45fps is plenty.   

2nd others have tried this and realised vram not that important beyond 12gb

3rd DCS is more CPU bound typically so check your frametime on CPU.

Don't think worth upgrading at all... much better use the money to buy a better VR headset...that will really change your experience.

[obious]

21 minutes ago, Brainfreeze said:

1st you do not need 90fps to be smooth and fluid.  45fps is plenty.   

2nd others have tried this and realised vram not that important beyond 12gb

3rd DCS is more CPU bound typically so check your frametime on CPU.

Don't think worth upgrading at all... much better use the money to buy a better VR headset...that will really change your experience.

Thanks for your input. I can’t speak to points 2 & 3 but I think you’re wrong on point 1 (albeit its a very subjective thing) as I used to lock frames to 45fps and use motion repro but the jaggy lines were horrible; 45fps is definitely not plenty 

[Raven (Elysian Angel)]

Yes it makes a massive difference: for VR with a Reverb you'd want at least a 6800XT/6900XT or 3090 if you want terrain textures on High.

You might want to check the hardware subforum as well: there are about a million existing threads about this very subject.

[edmuss]

As quoted really, DCS will allocate all the VRAM available but I don't think it really uses much more than 10-12. Certainly the higher the resolution, the more you need.

By my reckoning, the CPU is going to be pulling your frames down way before the GPU runs out of horsepower, it's just a function of how the current engine works.

5800x3D and a 3080ti now and I can get 90fps but with the same settings I can also get 50fps because the engine has dragged it down to the lowest common denominator. Better to tune to get a smooth experience and have improved visuals because you're not compromising on the GPU settings to attempt to crutch the CPU.

30 minutes ago, Brainfreeze said:

1st you do not need 90fps to be smooth and fluid.  45fps is plenty.   

2nd others have tried this and realised vram not that important beyond 12gb

3rd DCS is more CPU bound typically so check your frametime on CPU.

Don't think worth upgrading at all... much better use the money to buy a better VR headset...that will really change your experience.

edit: just for reference, I could run high textures on my 8gb 3070. Was it slower? Yes slightly, by about 2ms, but it still worked fine.

Edited September 7, 2022 by edmuss

[edmuss]

9 minutes ago, obious said:

Thanks for your input. I can’t speak to points 2 & 3 but I think you’re wrong on point 1 (albeit its a very subjective thing) as I used to lock frames to 45fps and use motion repro but the jaggy lines were horrible; 45fps is definitely not plenty 

45fps is plenty with openxr, jagged lines is nothing to do with reprojection, that's aliasing.

For reference I now run the G2 at 3100 resolution, high settings in DCS throughout with MSAAx2 + MFAA and reprojection unlocked and it's buttery smooth, no shimmer and no jagged anywhere. On Caucasus it runs at 45hz reprojection, on Syria it runs at 45hz and 30hz over the cities.

By locking the frames to 45 and enabling reprojection your absolutely castrating the system because it needs to be above half refresh (45) for the reprojection to work in the first place!

[obious]

3 hours ago, edmuss said:

45fps is plenty with openxr, jagged lines is nothing to do with reprojection, that's aliasing.

For reference I now run the G2 at 3100 resolution, high settings in DCS throughout with MSAAx2 + MFAA and reprojection unlocked and it's buttery smooth, no shimmer and no jagged anywhere. On Caucasus it runs at 45hz reprojection, on Syria it runs at 45hz and 30hz over the cities.

By locking the frames to 45 and enabling reprojection your absolutely castrating the system because it needs to be above half refresh (45) for the reprojection to work in the first place!

Are you using openxr or SteamVR?

Also, are you not contradicting yourself by saying you’re running 45hz reprojection yet doing so will castrate the rig? 

[edmuss]

I'm using openxr as it's far superior to steamvr for a number of reasons.

No, reprojection is a technique developed by Oculus years ago to give the perception of achieving refresh rate when the hardware simply cannot do it. If the refresh rate isn't achieved then it renders at half refresh rate (45Hz) and interpolates synthetic frames in between the rendered ones. You can be getting 11.5ms frametimes (87fps) and the reprojection will be at 45Hz, you're still rendering 87 of the 90 frames every second.

Reprojection has a computational overhead, typically this is 3-5ms. In order to achieve the refresh rate target of 22ms for 45Hz you must subtract this overhead from your appGPU frametime. Therefore in order to keep reprojection enabled you need your appGPU to be 22ms minus the overhead of 4ms which is 18ms.

If you've locked the framerate to 45 (22ms) then reprojection will be disabled in steamvr (because you've missed the refresh rate target and it can't reproject below half refresh) and it will be janky as hell. In openxr in the same situation it will step down to the 30Hz (1/3 refresh rate) bracket (which actually does work incredibly well).

The concept of locking the framerate with openxr is only for use when reprojection is off, in this instance you're relying on the vsync only to smooth head movements; rotations will be smooth, translations not so much until you get above around 60fps (below 16ms). The thought was why render more frames than you need to, save heat and energy; the sweet spot was found to be high 50s to 60s not 45.

Personally I'd rather have the framerate unlocked at all times.

[obious]

23 minutes ago, edmuss said:

Personally I'd rather have the framerate unlocked at all times.

Got it. So if I understand correctly, you haven't changed any OpenXR Toolkit settings, you've just cranked up the eye candy settings in DCS?

[edmuss]

Pretty much, I use foveated rendering on quality/wide and that's about it apart from some post processing bits like world scale and lighting.

[obious]

24 minutes ago, edmuss said:

Pretty much, I use foveated rendering on quality/wide and that's about it apart from some post processing bits like world scale and lighting.

That’s exactly what I’ve done but am getting horrible frame rates and a really stuttery experience

Edited September 7, 2022 by obious

[edmuss]

Have a read through Thud's guides   for system tuning and do it all, no skipping steps unless they don't apply to your system. There can be a load of reasons why performance isn't good, it's easier to identify bottlenecks if you know the system is properly sanitised and tuned.

Once your system is known good abs running cleanly then you can start to interrogate your frametimes and to where the bottlenecks are

[Burt]

1 hour ago, edmuss said:

In openxr in the same situation it will step down to the 30Hz (1/3 refresh rate) bracket (which actually does work incredibly well).

This is the main reason why I choose OXR over Steamvr, it’s seamless when this happens on my rig. Im running 90hz w/ MR.