Question about SLI, V-Sync (Smooth), and Half-Refresh V-Sync

Discussion in 'Videocards - NVIDIA GeForce Drivers Section' started by BlindBison, Nov 24, 2019.

  1. BlindBison

    BlindBison Master Guru

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    Hi there guys,

    Regarding SLI and its unique V-Sync mode "V-Sync (Smooth)", if one is playing at 30 fps on a 60 hz panel, does V-Sync (Smooth) act properly like "Half-Refresh V-Sync" or not?

    For example, if one is playing at 30 fps, my understanding is that they should use Half-Refresh V-Sync rather than standard V-Sync (Nvidia has a setting in their control panel called Half-Refresh Adaptive V-Sync for example).

    So, you might be asking, why don't I just force that Half-Refresh mode instead of V-Sync (Smooth)? Here (https://displaylag.com/reduce-input-lag-in-pc-games-the-definitive-guide/), it was found in these tests that V-Sync (Smooth) actually had the lowest input lag of the traditional V-Sync modes by a slight margin so it would seem its preferable to use for SLI users wanting to V-Sync their games.

    However, what I don't know and what I've been unable to find anywhere online is whether or not V-Sync (Smooth) behaves correctly like "Half-Refresh" V-Sync if a user caps their framerate to 30 fps for example.

    I have an older gaming laptop at this point with SLI GTX-770M's in it -- for some modern games that are heavier, what I'd really like to do then is use: "Half-Refresh V-Sync (Smooth)", but that's not an option in the default control panel, there's just "Half-Refresh Adaptive V-Sync" and "V-Sync (Smooth), but no "Half-Refresh V-Sync (Smooth)" unfortunately.

    So, is it an option in Nvidia Inspector that I'm missing perhaps? Or, does V-Sync (Smooth) already behave correctly like Half-Refresh V-Sync?

    I haven't been able to track that info down online so I figured I'd ask here -- anyway, thanks for your time, I really appreciate it!
     
    Last edited: Nov 24, 2019
  2. BlindBison

    BlindBison Master Guru

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    @RealNC I'm sorry to bother you, but I figured i'd tag you since historically you've known a lot about these sorts of things. In addition to the V-Sync (Smooth)/Half-Refresh V-Sync question and all that, interestingly, in that displaylag link in the OP, they found in their tests that lowering the Flip Queue size still reduced input lag when an fps cap was in place and V-Sync was engaged. This surprised me since iirc RTSS blocks prerendering (so perhaps the in-game limiter for Street Fighter IV does not?) and also BattleNonSense found in some of their tests that changing the flip queue did nothing inputlag-wise for some games so long as they had an fps cap in place (Overwatch/Battlefield for example iirc).

    Also surprising to me that V-Sync (Smooth) had the least input lag since SLI normally adds another frame of delay as I understand it at least (and did increase input lag with the standard V-Sync in their tests, but not V-Sync (Smooth)).
     
    Last edited: Nov 24, 2019
  3. BlindBison

    BlindBison Master Guru

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    UPDATE: It seems that in the Nvidia Profile Inspector, if one changes the V-Sync option in their Nvidia control panel first to "V-Sync (Smooth)", in Inspector this results in V-Sync being set to "Force ON" and V-Sync Smooth AFR behavior being set to ON while tear control is Standard.

    Within Inspector, it looks like you can force VSync to HalfRefresh then enable Smooth AFR behavior so I expect this is probably what one can do if they intend on playing at 30 fps with V-Sync Smooth.

    I'd close the issue, but doesn't look like I have that ability so figured I'd at least leave the update here, anyhow, thanks team.
     

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