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With new FPS counter in 2.8 how to tell if it's GPU or CPU bottleneck?


DmitriKozlowsky
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Following. Which frame time line is for which? I *think* green is GPU, and white is CPU?

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  • 1 month later...

I was looking for the answer to this one, too. I've gotten into both CPU and GPU limited situations (verified with other tools like FPSVR and the OpenXR toolkit), and in both cases, the white line seems higher. So I'm not totally sure what it's telling me right now. I would be very interested to hear something definitive.

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You can use the Windows Task Manager or MSI Afterburner tool to monitor GPU and CPU load.

The internal DCS tool only shows the total FPS (top scale) and Latency (bottom scale) in ms for the Frame (White), Simulation (Green) and Present (Yellow). I have no clue what Present is for. This won't help identify your bottleneck.

You can hover over with your mouse to see the numbers:

image.png   image.png

You are GPU bottlenecked if your GPU utilization hits 95-100% with uncapped framerate (no V-Sync enabled in 2D, no ASW/Motion Reprojection in VR enabled). This is the ideal case you should aim for. So this means the GPU pushes hard to get all possible FPS on the screen and there is no GPU-headroom left. CPU and game engine could possibly render more, but the GPU is the limiting FPS-factor.  You could reduce some graphics settings in-game and should gain some more FPS if this is your goal. This would look like this in MSI Afterburner:

image.png

You are CPU bottlenecked / engine bottlenecked when you have uncapped framerate (no V-Sync enabled in 2D, no ASW/Motion Reprojection in VR enabled) but the GPU utilization will not max at 95-100%. This is the difficult part. In This case it could be CPU limiting (2 cores maxed out at 100% load for DCS - difficult to see because the task scheduler changes the currently used cores frequently) or the engine of DCS is limiting itself. We all know the DCS engine does not run very well with a lot of units on the map, so keep that in mind. This would look like this in MSI Afterburner:

image.png

If you play in VR you should test this always with uncapped framerate - this means no ASW / motion reprojection enabled. Otherwise the FPS could get capped at your motion reprojection target (45 fps when 90 hz display is used for example) and the lower gpu load would be normal, because the gpu will not push higher above 45 fps until it could reach 90 fps technically. This implies your GPU is strong enough to go higher than 45 fps. If the GPU cannot even reach the motion reprojection target of 45 fps, the GPU utilization would max at 100% out for example with 38 fps.

Framerate (and Frametime) can also be monitored in MSI Afterburner:

image.png

Especially the frametimes (this is the consistency of rendered frames) are important in VR- huge spikes cause visual stuttering and can cause nausea. ASW or Motion Reprojection does not work very well on high-player-count multiplayer servers in DCS. Often the frametimes are all over the place in multiplayer compared to singleplayer. You can literally feel those spikes in VR:

image.png

So the more even and smooth (perfect would be a straight line) the frametime, the better the VR experience.

Since DCS 2.8.2.35632 Open Beta (25.01.2023) the GPU utilization is all over the place especially in VR and I suspect a game engine bug with the rendering.

Very often the engine is the limiting factor and can not utilize the best GPU/CPU combinations out there. This also happens alot in recent AAA games, when there is no modern and proper multi-core support for the CPU inside of the game engine.

I would not bother investing too much time in optimizing DCS settings right now. If we are lucky, the 4 core Multi-threading is coming in the next months, also DLSS is coming to DCS hopefully this year. Also the changes for VR (Native OpenXR support and some improvements there) could be a welcoming game changer this year.


Edited by Tepnox
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Ryzen 7 5800X3D // 64 GB RAM // RTX 3090 // Quest Pro

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