Does "Fast Sync" style V-Sync work best with multiples of monitor refresh? If so, why?

Discussion in 'Videocards - NVIDIA GeForce Drivers Section' started by BlindBison, May 3, 2022.

  1. BlindBison

    BlindBison Maha Guru

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    I've read online at various points that Fast Sync style triple buffering (last in first out triple buffering rather than first in first out style triple buffering as I understand it where intermediate frames can be tossed out and the last rendered frame is displayed when the monitor refreshes) was meant to be used with multiples of your refresh rate.

    E.g. If you have a 60 hz monitor but want to play CSGO or something, you could use Fast Sync then cap the game to 120 or 180 FPS with RTSS or some such. Maybe I'm misremembering or misunderstood, but I thought I remembered Alex from Digital Foundry mentioning this as well in passing in his V-Sync guide video from aways back.

    What I don't understand is, why would this be any better than just running the game uncapped with fast sync enabled? I understand the issue with Fast Sync is that when you look closely it ends up appearing very jittery as intermediate frames rendered by the game can be lost (though the upside is you don't get huge stutters when the framerate dips below refresh and latency is very low), but I'm not seeing how capping to a multiple would make this any better than just letting the game run free.

    Have I missed something? I've never seen this explained before and I'm not sure even how it started that Fast Sync was intended to be used with multiples of refresh, I've just seen it tossed around/mentioned now and again with no explanation as far as I recall. Thanks!

    As an aside, in my opinion every game that ships on PC should have a built in option for half-refresh V-Sync (they're already usually doing this on console from what I gather and this would help lower spec/lower end PCs quite a bit I think) and they should also expose internally whatever FPS limiter they're using in conjunction with v-sync to users if applicable -- for example games like Hunt Showdown now auto-fps cap to refresh when V-Sync is ON to reduce latency as I understand it). This matters because for laptops with optimus you cannot force half refresh v-sync from the control panel in my experience (though in game options do work) and also users need to know whether or not the game is auto-capping fps internally in conjunction with v-sync so that we know whether or not to use an external limiter like RTSS to make our own low lag v-sync solution (see blurbuster's low lag v-sync guide for what i'm referring to). Since I'm kina ranting anyway :p Please devs for the love of god fix your games to prevent this epidemic of asset streaming and shader compilation stutter that's been going on recently (UE4 PC ports, Elden Ring, etc).
     
  2. Astyanax

    Astyanax Ancient Guru

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    not really, fast sync just likes to be as fast as possible so it has ample enough frames ahead to discard without jerky frames.
     
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  3. BlindBison

    BlindBison Maha Guru

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    Thanks that's helpful -- yeah, I don't really understand exactly what capping the framerate to multiples of refresh would achieve as an improvement over just running uncapped, but I've heard people express this notion pretty frequently so I wondered if there was something to it.
     
  4. user1

    user1 Ancient Guru

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    from what I remember when messing around the setting, fast sync does try to "stick" to multiples of your refreshrate, The reason it does this is that if your monitor is 60hz and your framerate is 180, there will always be a frame ready immediately for the monitor since the framerate is a multiple of the refresh rate( in this case every 3rd frame is sent to the monitor). If the framerate is not a multiple of your refreshrate, it means that you have to potentially wait a full frame interval ,if you want to prevent tearing, this is why fastsync produces a stuttering effect at low framerates.
    this is because fastsync doesn't or tries not to buffer frames like normal vsync, inorder to reduce latency.

    I don't see any reason to cap the framerate, other than maybe just to reduce power consumption. definitely won't improve anything performance wise when using fast sync.
     
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  5. BlindBison

    BlindBison Maha Guru

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    Thanks that's helpful to know!
     

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