Is the 'G-sync Ceiling' the same thing as the 'Nvidia-G-sync-Aware-V-sync'?

Discussion in 'Videocards - NVIDIA GeForce Drivers Section' started by BlindBison, Jul 27, 2018.

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  1. BlindBison

    BlindBison Master Guru

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    Hi there,

    Recently I was reading these two articles about G-sync technology and the best practice to avoid latency and the G-sync ceiling:

    https://www.howtogeek.com/270672/how-to-enable-optimize-and-tweak-nvidia-g-sync/

    https://www.blurbusters.com/gsync/gsync101-input-lag-tests-and-settings/5/

    My understanding after reading through these is that the "G-sync Ceiling" is the point at which Nvidia's G-sync Aware Vsync will kick in -- so, this should kick in above 144 hz on a 144 hz monitor then for example.

    To get around this, people seem to have simply capped their fps 2 frames below their monitor refresh rate (I'm guessing 2 frames instead of 1 to get around frame limiter variance since some frame limiters aren't as accurate as Rivatuner, but provide lower latency for example).

    What I'm confused about then is about the V-sync option in the Nvidia Control Panel.

    > Doesn't turning V-sync to OFF in the Nvidia Control Panel (while leaving G-sync on) remove/disable the Nvidia G-sync Aware V-sync meaning there no longer exists a G-sync Ceiling?

    I would think that if you disabled the G-sync Aware Vsync in the control panel while leaving G-sync on that one could limit their fps to their full refresh rate without any penalty since a G-sync ceiling/G-sync Aware V-sync would no longer kick in to increase latency.

    I guess I'm asking what am I getting wrong in all this? If you can just turn off the G-sync ceiling/G-sync Aware Vsync, it would seem like there's no longer any need to limit fps 2-3 frame beneath -- rather I would think you could simply limit the fps to your refresh rate or maybe 1 below to get around frame limiter variance.
     
  2. Agent-A01

    Agent-A01 Ancient Guru

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    Turning VSync off(Default) in NVCPL allows the FPS to go above the refresh rate without any restrictions.

    Enabling VSync enables FTC(frame time compensation) in Gsync mode which allows perfect synchronization to the monitors vblank interval; it will eliminate tearing.

    Without Vsync on, you can get very minor tearing under Gsync mode even within Gsync's range.

    When your FPS = refresh rate with vsync ON, Gsync deactivates and all latency caused by vsync is in effect.

    So the point is you want to enable Vsync for FTC to have zero tearing and setting a FPS limit below the Gsync ceiling to eliminate any lag imposed by vsync on when FPS=refresh rate.
     
  3. RealNC

    RealNC Ancient Guru

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    The safest value to cap to is -3FPS. -2FPS was tested to works fine, while -1FPS was shown not to work well. So -3FPS seems to be a good value in order to be sure you avoid vsync-like behavior.

    As for disabling vsync when using gsync, pretty much what Agent-A01 said. Disabling it can result in tearing even at lower frame rates (like 120FPS on a 144Hz mode) and will certainly result in tearing once you're near 143FPS.

    Gsync ON vsync OFF requires very evenly spaced frame times in order to not have tearing. If there's any big frame time variation, you will get tearing, usually at the bottom of the screen. Enabling vsync will apply small corrections to gsync that compensate for these frame time variations at virtually no additional latency cost (the compensations are only delaying frames by just enough scanlines so that the tear line is hidden past the bottom of the screen, which is exactly what we want.)
     
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  4. BlindBison

    BlindBison Master Guru

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    @Agent-A01

    Thank you for explaining all of that, I really appreciate it. You've led me to another question with all of that.

    Alright -- suppose I have G-sync enabled, V-sync enabled in the control panel, and I frame-limit 2 frames beneath my refresh rate to avoid the traditional Vsync from kicking in.

    Based on what you said, the traditional Vsync will still kick in from time-to-time since G-sync by itself can result in some minor tearing.

    > When that traditional Vsync kicks in then, won't it still impose a latency penalty?

    Also, is Vsync ON in this case just traditional Vsync or is it some new variant optimized to work with G-sync? I would think if it was some new variant they would have named it differently.

    Thanks for your time.
     

  5. RealNC

    RealNC Ancient Guru

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    Nope! What happens here is a minor adjustment to when exactly the frame is sent to the monitor. There's no actual "full" vsync being engaged here.

    It's just a switch that enables frame time variance compensation.
     
  6. BlindBison

    BlindBison Master Guru

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    @RealNC

    Thank you very much -- that explains everything I was wondering about then. I appreciate it.
     
  7. Martigen

    Martigen Master Guru

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    I've always found this, and the blurbuster's article, interesting -- does anyone know why Nvidia hasn't modified gsync in the drivers so that people don't have to fart-arse around with vsync settings and FPS capping? You know, just have a 'G-sync' toggle and that's it. Surely nvidia is aware of this...
     
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  8. mahanddeem

    mahanddeem Master Guru

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    I cap my fps to 140 on my PG279Q. And of course enable vsync in NVCP, while turn it off in games.
     

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