bapt337 wrote: ↑11 Apr 2020, 19:21
allright so vsync ON ITS OWN doesnt lock frametime, but lock framerate, right?
There isn't a simple answer to this, and really, it's complete off subject for this thread, but I'll quote a couple of (grossly simplified) excerpts from the comments section of my article regarding this (ignore anything that refers to "G-SYNC"; the below applies to any form of sync with framerates sustained above the refresh rate):
Even though [V-SYNC] visibly “caps” the framerate to the refresh rate, double buffer V-SYNC (with or without G-SYNC) doesn’t prevent delayed frame delivery like a framerate limiter does, but, in fact, causes it.
For instance, at a sustained 200 FPS, each frame is rendered in 5ms. However at 144Hz with G-SYNC and/or V-SYNC, the fastest each frame can be delivered tear-free to the display is 6.9ms. So, with 144Hz G-SYNC + V-SYNC at 200 FPS with no FPS limiter (which effectively behaves like standalone V-SYNC at that point, as G-SYNC can no longer adjust the refresh rate to the framerate), each frame will be rendered in 5ms, but each will be delayed 1.9ms before being delivered as to match the max 144Hz scanout cycle of 6.9ms per. This delay adds up over a period of frames, eventually over-queuing the buffers, and thus causes the extra input lag.
A framerate limiter, however (in-game or external), ensures that the maximum render time of each frame is within the maximum delivery time of the given refresh rate, preventing this issue entirely.
And further...
The higher the FPS is above the refresh rate with V-SYNC, the worse the input lag is, as your inputs are being read at lower and lower render times, but being forced to be shown at the same intervals of the current max refresh rate regardless.
Basically, V-SYNC with framerates above the refresh rate are always a big no-no input lag-wise, and an FPS limit set below the refresh rate is recommended.
FYI, V-SYNC with a 59 FPS limit @60Hz is much lower lag than uncapped adaptive V-SYNC @60Hz. Also, Nvidia adaptive V-SYNC is merely V-SYNC "on" with framerates above the refresh rate, which then switches to V-SYNC "off" with framerates below the refresh rate.
If you want to discuss this subject further, feel free to create a new thread on it (same goes for frametime stability and pacing in general as well), but I've about exhausted my ability to convey it here in the context of our current discussion, which is actually about LLM.
Getting back to the LLM subject, to sum-up, you typically don't need it for Scanline Sync, and it's only primarily useful in GPU-bound situations.