this post was submitted on 28 Sep 2025
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It's because game logic is calculated on real frames and these things lower the real frame rate even though they give you more rendered frames. If you were getting 40 real FPS, and then you go to 30 real fps, you will feel a significant amount of lag even if you are getting 60 fps in fake frames. Basically the game loop is running slower and stuff like input polling is happening slower even if you have a higher frame rate.
Framegen is worse the lower your base frame rate is.
The penalty to the speed at which the game runs is much more significant, if you normally run at 40 fps and framegen gives you 60 (30 real) then you have introduced 8 ms of latency just from that. While the same 25% performance cost going from 180 fps to 270 (135 real) adds just 2 ms.
The lower your real frame rate is the harder it will be to interpolate between frames because the changes between frames are much larger, so it will look worse. Also the lower your frame rate the longer any mishaps will remain on screen, making them more apparent.
True, Ig I was trying to teach people about why FSR often causes input lag. If you are getting 120 real frames then yeah, it probably won't matter much, but if you are getting less then 60 real frames it's going to be a worse experience unless you are playing menu games or something.
Yeah I just wanted to illustrate that with some numbers :)
It's a bit counter-intuitive that frame generation is worse the lower your base frame rate is. And Nvidia in particular has no interest in making it clear that this tool is only really good for making a well-running game run even better, and is not going to give your 5070 "4090 performance" in any meaningful way.
Frame generation shouldn't be a bottleneck on the CPU though, should it? That stuff is happening on the GPU. I know I saw a video about this stuff but I can't remember the real reason input lag increases with frame generation/interpolation.
Most games aren't bottlenecked by your CPU at all. It spends a lot of time waiting for the GPU to be done drawing you a picture.
"Why isn't the game doing other stuff meanwhile?" you might ask, and part of the answer is surely, "Why do stuff faster than the player can see?", while another part is likely a need to syncronize the simulation and the rendering so it doesn't show you some half-finished state, and a third part might be that it would be very confusing for the player to decouple the game state from what they see on screen, like you see yourself aiming at the monster, but actually it moved in between frames so your shot will miss even if the crosshair is dead on.
I didn't mean the game loop being bottlenecked, I said frame generation. But yeah, all that is also true, I know. 👍
I was trying to explain why the game loop would be held back by the rendering speed, even though they run on different hardware.
If you are bottlenecked by the GPU that means the game loop spends some of its time waiting for the GPU. If you then turn on frame generation, you devote parts of the GPU to doing that, which makes regular rendering slower, making the game loop spend even more time waiting. This will increase input latency.
Frame generation also needs to delay output of any real frame while it creates and inserts a generated frame. This will add some output latency as well.
In the opposite scenario, where you are bottlenecked by the CPU, enabling frame generation should in theory not impact the game loop at all. In that case it's the GPU that's waiting for the CPU, and it can use some of those extra resources it has to do frame generation with no impact on input latency.
Maybe it's not the CPU but with FSR either way the real frame rate drops which is why you get input lag. The game logic/game loop is only calculated per real frame. Which means if you take a 20% drop in real frame rate you are going to get 20% more input lag.
Isn't FSR supposed to give better performance/real fps?
If you get higher real FPS via upscaling, and a lower resolution. It can improve input latency and sim speed.
It is (if we talk about FSR as upscaler tech). But it wont help in CPU bound scenarios where the GPU already has to wait for CPU.
And in that case, frame generation will cause even more input lag I guess. I'm thinking frame generation is best for systems where the GPU is the bottle neck, I guess, input lag wise? Where it gets served frames ASAP, and can interpolate frames as soon as the latest, and second latest frames are available. Which it does anyway, but it has to wait less, then.
it’s not. The whole point of FG was to take advantage of high refresh rate monitors as most games can’t render 500FPS even on the fastest CPU… alas, here we are with games requiring FG to get you to 60FPS on most systems looks at Borderlands 4 and Monster Hunter Wilds
Right, but FG shouldn't be touching the CPU in any way, should it? It should be a local thing on the GPU transparent to the CPU, unless I'm misunderstanding how it works.
It's not using CPU
Then I don't understand how it would affect the game loop negatively. I'll look into it though, will do some research.
Because the "delayed" or real input does not correspond to the image you see on the screen. That's why FG is most useful when you already have high base framerate as the input gets significantly lower and the discrepancy between the felt input and perceived image narrows.
Example:
30FPS is 33.3ms frame to frame latency (+ something extra from mouse to displayed image for input)
With 2x FG you get at most 60FPS assuming there's no performance penalty for FG. So you see 16.6ms + mouse to display frame to frame but input remains 33.3ms + mouse to display.
Same from base 60FPS 16.6ms to FG 120FPS 8.3ms perceived but 16.6ms+
Same from 120FPS 8.3ms base to FG 240FPS 4.15ms perceived...
As you can see the difference in input gets smaller and smaller between base FPS and FG FPS as you're increasing the base framerate.
This is however a perfect scenario that does not represent real world cases. Usually your base FPS fluctuates due to CPU and GPU intensive scenes. And during those flucfuations you will get big inpuy delay spikes that can be felt a lot as they suddenly widen the range between perceived image and real input... Couple that with the fact that FG almost always has a performance penalty as it puts more strain on the GPU so your base framerate and therefore input will be automatically higher.
https://lemmy.world/comment/19685489