G-SYNC 101: In-game vs. External FPS Limiters


Closer to the Source

Up until this point, an in-game framerate limiter has been used exclusively to test FPS-limited scenarios. However, in-game framerate limiters aren’t available in every game, and while they aren’t required for games where the framerate can’t meet or exceed the maximum refresh rate, if the system can sustain the framerate above the refresh rate, and a said option isn’t present, an external framerate limiter must be used to prevent V-SYNC-level input lag instead.

In-game framerate limiters, being at the game’s engine-level, are almost always free of additional latency, as they can regulate frames at the source. External framerate limiters, on the other hand, must intercept frames further down the rendering chain, which can result in delayed frame delivery and additional input latency; how much depends on the limiter and its implementation.

RTSS is a CPU-level FPS limiter, which is the closest an external method can get to the engine-level of an in-game limiter. In my initial input lag tests on my original thread, RTSS appeared to introduce no additional delay when used with G-SYNC. However, it was later discovered disabling CS:GO’s “Multicore Rendering” setting, which runs the game on a single CPU-core, caused the discrepancy, and once enabled, RTSS introduced the expected 1 frame of delay.

Seeing as the CS:GO still uses DX9, and is a native single-core performer, I opted to test the more modern “Overwatch” this time around, which uses DX11, and features native multi-threaded/multi-core support. Will RTSS behave the same way in a native multi-core game?

Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings

Yes, RTSS still introduces up to 1 frame of delay, regardless of the syncing method, or lack thereof, used. To prove that a -2 FPS limit was enough to avoid the G-SYNC ceiling, a -10 FPS limit was tested with no improvement. The V-SYNC scenario also shows RTSS delay stacks with other types of delay, retaining the FPS-limited V-SYNC’s 1/2 to 1 frame of accumulative delay.

Next up is Nvidia’s FPS limiter, which can be accessed via the third-party “Nvidia Inspector.” Unlike RTSS, it is a driver-level limiter, one further step removed from engine-level. My original tests showed the Nvidia limiter introduced 2 frames of delay across V-SYNC OFF, V-SYNC, and G-SYNC scenarios.

Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings

Yet again, the results for V-SYNC and V-SYNC OFF (“Use the 3D application setting” + in-game V-SYNC disabled) show standard, out-of-the-box usage of both Nvidia’s v1 and v2 FPS limiter introduce the expected 2 frames of delay. The limiter’s impact on G-SYNC appears to be particularly unforgiving, with a 2 to 3 1/2 frame delay due to an increase in maximums at -2 FPS compared to -10 FPS, meaning -2 FPS with this limiter may not be enough to keep it below the G-SYNC ceiling at all times, and it might be worsened by the Nvidia limiter’s own frame pacing behavior’s effect on G-SYNC functionality.

Needless to say, even if an in-game framerate limiter isn’t available, RTSS only introduces up to 1 frame of delay, which is still preferable to the 2+ frame delay added by Nvidia’s limiter with G-SYNC enabled, and a far superior alternative to the 2-6 frame delay added by uncapped G-SYNC.



1046 Comments For “G-SYNC 101”

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Agitatio
Member
Agitatio

Thank you for your hard work on this in-depth guide jorimt! Wanted to ask a quick question about one of the notes in you closing FAQ:

As such, it is recommended to keep G-SYNC set to “Enable for full screen mode” globally, and then to use Nvidia Profile Inspector (download here) to set both “G-SYNC – Application Mode” and “G-SYNC – Global Mode” to “Fullscreen and Windowed” per game profile, as needed:

What is the difference between those to variables and is there a benefit to changing them both? I noticed that changing only the Application Mode while keeping Global Mode unchanged does still work.

Taleuxss
Member
Taleuxss

why’d you ask, “Enable for full screen mode” or “Enable for windowed and full screen mode” in the NVCP? is there a downside to windowed being enabled

BlackStorm82
Member
BlackStorm82

[240hz monitor]
Set to 60hz (vsync off / gpu 70%)
300FPS limit

set to 240hz (vsync off / gpu 70%)
300fps limit

Are input lag the same?
Is 240hz 300fps better?

dop3boost
Member
dop3boost

Hello i have problem with my gsync monitor

Basically it is not working on apex LEGENS anymore.
My settings
VSYNC ON THE PANEL
GSYN ON
IN-GAME FPS LIMIT 190
Alienware Aw2518h 240hz
already installed drivers and reinstalled but they are not the drivers already installed more than 6 times new and old.
So I had a question, is there a way to force the game to run 240hz because the game won’t let me choose my monitor’s hz?

my pc
i7 9700k
GTX 2080 SUPER
32GB RAM Etc etc

could you help me I don’t know why gsync doesn’t want to work in another game it works perfectly.

hramulka
Member
hramulka

Hello! It’s me again. Released a new driver 451.67 and again checking G-Sync + nvcp V-Sync + LLM Ultra, and again there is no auto limit of 158 fps on 165 Hz monitor. It turns out that with the output of drivers 451.48 & 451.67, LLM ultra does not set an auto limit, so there is no error, as you thought earlier. If you have time, please double-check. This means that The low Latency Mode* Settings item will have to be rewritten.

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