bapt337 wrote: ↑16 Apr 2020, 02:36
Ive got a question, if you cap fps at 61 for 60hz, with vsync on, and its a gpu bound situation (CPU faster than GPU), then the maximum pre rendered fame is always 1 cause i force it by giving only one extra frame (cap 61), even if buffer size is 2 or 3 right?
No.
The 1 frame difference between 60 FPS and 61 FPS is not the same thing as 1 pre-rendered frame. With pre-rendered frames, it doesn't matter what the average framerate number is (it could be 61, 82, 99, 1003, 25, 42), it matters how that average framerate is currently being generated.
If the average framerate is 61 because the framerate is uncapped and the GPU is maxed out, it means the system can only generate a average max framerate of 61 FPS, at which point the pre-rendered frames queue increases to wait for the GPU to be ready for the next frame(s).
However, if the average framerate is 61 because you're using an FPS limiter to keep it there, so long as the GPU isn't maxed using this limit, this means the system could otherwise output a higher average framerate due to the remaining CPU/GPU overhead available, at which point, since the CPU doesn't need to wait on the GPU, the pre-rendered frames queue is decreased, and the CPU is able to hand frame information over to the GPU without wait (or with less wait).
bapt337 wrote: ↑16 Apr 2020, 02:36
But if fps for example fps go down to 45fps, in this case frame buffer gonna be full cause i give 61 fps (fps cap) so if the gpu can only render 45fps in one second then it give 16 extra fps (61-45) then buffer will be full and even more filled by the extra frame and the max pre rendered frame setting take effect at this moment if im right
Again, the pre-rendered frames queue isn't directly related to the difference in average framerate between scenario A and B, it's related to how that average framerate is being generated at any given point.
In your posed scenario, uncapped 45 FPS is going to have a higher pre-rendered frames queue because whatever scene is occurring is giving the GPU a harder time than the capped 61 FPS scenario; in the former scenario, the GPU is maxed out, and in the latter scenario, it is not.
That's what makes the primary difference with the pre-rendered frames queue.
andrelip wrote: ↑16 Apr 2020, 07:26
With that in mind, you can think in scenarios that is not too obvious and that is caused when one of that sources have more impact than the others.
Yeah, I haven't watch it since it originally released, but I vaguely recall...
1. They may have been conflating different causes of input lag, which didn't muddy their results as much as it did their conclusion of their results.
2. They didn't seem to understand that external FPS limiters reduce input lag less than some in-game limiters, and further, that some in-game limiters reduce input lag about the same as external limiters.
The whole point was to measure the input lag difference incurred by GPU usage only, but instead, they may have conflated that with differences in FPS limiter input lag, and possibly even V-SYNC and framerate input lag.