I always seem to have a CPU bottleneck in MSFS2020, and often find myself fiddling with settings to try and alleviate that. I tend to find that games (especially MSFS) tend to have better frame consistency when the GPU is the limit, rather than the CPU, as the CPU tends to spike and cause dips in FPS and/or micro stutters.
Context: My CPU is decent, a 5900x, and I have tonnes of good RAM, it’s all overclocked and liquid cooled, so it’s frustrating that the CPU bottlenecks so easily in flight sim, but I do also have a 3090, so, perhaps that’s why.
Method: Anyway, to do this, I put every single setting on low, and dropped the render scale slider to the lowest number, spawned into Heathrow R27, and checked that the CPU was the limit (Mainthread limit), and what FPS I got - it was, and I got 73 FPS (flitting between 72-74). I then, one at a time, put each setting (other than render scale) up to it’s max value, to see if/how it affected FPS.
Results: It turns out hardly ANY settings at all, made any impact whatsoever to FPS, i.e. they didn’t impact the CPU, since that was the bottleneck. So it’s easier to talk about the ones that did affect the FPS. Those were: Buildings (3 FPS), Terrain Shadows (5 FPS), and maybe Water Waves and Raymarch Reflections at ~1 FPS each.
Terrain LOD and Objects LOD were (obviously) the worst culprits, so I’ll come back to them.
I then turned every settings from the lowest the max other than Render Scale, Terrain LOD, Objects LOD and I was down to 66 FPS, still CPU bottlenecked. This was pretty good IMO, I’ve lost less than 10% of frames, by sticking basically everything at max settings.
Then we come to the LODs. Again, starting with everything else on min settings, I increased Objects LOD from 25 (73 FPS) to 70 (69 FPS), then 100 (68 FPS), then 150 (67), then 200 (66 FPS). So it’s fair to say that once you bump it up above minimum, you lose ~7%, and then you might as well go all the way, since you only lose about 10% total with it on 200.
Terrain LOD is a different story however, same as above, starting with everything on min, and T LOD at 25, 73 FPS. Then at LOD 100 (65 FPS), 200 (58 FPS), 300 (53 FPS), 400 (49 FPS). So Terrain LOD is very much more linear, the further you go, the more it impacts your CPU
Caveats: The test was very limited, but also only took about 10 minutes to glean some important insights. It’s worth pointing out that one of those limits is that by it’s nature, sitting on R27 of Heathrow, you can’t see any water, which is perhaps why Water Waves had only a questionable 1 FPS impact. There are other settings I can’t pretend to know exactly what they do, and if they would have impacted the CPU more in a different location/setting/test.
Conclusions: Not much affects the CPU, except for LODS. I will fly for a while with everything on max settings, including Objects LOD at 200, but Terrain LOD at 100, this brought me to around 53 FPS. I’ll see how much it seems to affect general flying, and if the low TLOD annoys me. If it does, I’ll knock it up to 200, which will leave me at 46 FPS. The GPU is basically never a problem, even at 100 renderscale, although this does change slightly with the Aero at highest PPD settings. I will play some more, and it might be that I prefer high PPD and DLSS Quality, or lower PPD and TAA-100, we’ll see. But I’m pleased to have finally identified (on MY system) which settings affect the CPU, since that’s my main bottleneck.
