Any downside to enabling G-Sync for Windowed Mode? It's only enabled for Fullscreen by default

Discussion in 'Videocards - NVIDIA GeForce Drivers Section' started by BlindBison, Aug 4, 2020.

  1. BlindBison

    BlindBison Master Guru

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    upload_2020-8-3_22-20-7.png
    I noticed here that G-Sync was not enabled for Windowed mode by default -- is there any reason not to turn this on for both? Certain games appear to lack an exclusive fullscreen mode (much to my dismay given exclusive fullscreen's benefits) and iirc by default windowed mode forces a sort of triple buffered fast sync of sorts (which can appear rather jittery -- Digital Foundry talked about how Windowed mode handles tearing in their V-Sync video I recall though perhaps I’m misremembering).

    What I'm worried about is, how is G-Sync handled in windowed mode? Does it cause issues or some such (hence it not being enabled by default perhaps)? Typically for G-Sync (in fullscreen mode) you would cap FPS to ~3 beneath refresh, but in windowed I wonder how that would work since if you've got a game in a window on your desktop running at 141 FPS while the desktop itself is set to refresh at 144 FPS, would that cause some weird behavior? Or, does the whole desktop run at the fps of the windowed game to avoid this issue?

    Anyway, just wondering what I should do here -- thanks for your help and time!
     
    Last edited: Aug 30, 2020
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  2. fantaskarsef

    fantaskarsef Ancient Guru

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    Curious about that too.
     
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  3. endbase

    endbase Master Guru

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    Same here
     
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  4. chr!s

    chr!s Member Guru

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    yea, so I've noticed some weird behaviour - at some point, corsair's iCUE software would cause the desktop to stutter. The other application was "windows terminal" . there could be others. So not sure if it's on the nvidia side or if it's on the 3rd party application side - because for example certain versions of iCue worked fine.. and you may find the latest iCue works fine. I ended up leaving the default (Full screen only) as all the games i play have exclusive full screen.
    I suppose turn it on for both full and windowed - and see how your applications react.. you will definitely notice the stuttering if it happens.

    Not sure if I can post links - but here is an example on reddit;
    https://www.reddit.com/r/buildapc/comments/a1q87y/desktop_stuttering_with_gsync_enabled_for/

    edit: here is the corsair forum;
    https://forum.corsair.com/v3/showthread.php?t=183504&highlight=mouse+lag

    anyway, you may find the the these issues are resolved.?


    edit 2:
    example on the nvidia forum;
    https://www.nvidia.com/en-us/geforc...rivers/13/292506/g-sync-mouse-lag-in-windows/
     
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  5. fantaskarsef

    fantaskarsef Ancient Guru

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    ^ I noticed something similar with Libre Office. Shows the FPS counter which is like 15 or lower, although I couldn't care less about Gsync in an office application...
     
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  6. Cave Waverider

    Cave Waverider Master Guru

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    Yes, that's likely why it's disabled by default. However, there don't seem to be that many applications that cause this (at least from my testing). One can leave it enabled for Windowed and Full Screen mode and simply add/edit a profile for the misbehaving program via Nvidia Profile Inspector and disable G-Sync for that program alone, which may make more sense for some users than keeping G-Sync windowed mode disabled overall.
    Maybe it would also work the other way around, but I haven't tested it.
     
    Last edited: Aug 6, 2020
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  7. aufkrawall2

    aufkrawall2 Master Guru

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    There is no ULL support for borderless and having DWM in between is just another (certain) source of failure. Avoid at all costs and don't bother. :)
     
  8. BlindBison

    BlindBison Master Guru

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    @aufkrawall2 I'm sorry, do you mean avoid G-Sync in windowed mode when you say, "Avoid at all costs and don't bother" or are you replying to someone else in the thread? I expect ULL is referring to Ultra Low Latency and DWM is referring to the Windows Desktop Manager. Just want to be sure I'm understanding your meaning correctly. Thanks,

    @Cave Waverider Thanks, that's helpful to know
     
  9. aufkrawall2

    aufkrawall2 Master Guru

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    ULL has no effect in borderless mode and borderless mode itself is a source of unnecessary issues with Gsync.
    So, yeah: Just avoid borderless mode for Gsync altogether. If you need to enable it for some crappy Unity Engine game that offers no fullscreen exclusive mode, there is a good chance that it will show weird stutter regardless. So Gsync for borderless is close to, if not entirely useless anyway.
     
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  10. BlindBison

    BlindBison Master Guru

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    Thanks, that's a helpful perspective to have -- I wonder why it could cause such behavior, huh.

    Interestingly here: https://blurbusters.com/gsync/gsync101-input-lag-tests-and-settings/10/ it does seem that G-Sync does bypass the added input delay of the DWM. What I may try is in various windowed games manually trying windowed with G-Sync ON VS OFF to see what occurs.

    I have noticed some windowed only games stuttering really badly (such as Journey on the EPIC store much to my dismay), but I'm presently unsure if that's due to G-Sync in windowed mode or the game just being jank and/or the Windowed mode V-Sync implementation (which Digital Foundry had stated in their V-Sync video is sorta like triple buffered fast sync which is jittery).

    In particular, I'm confused about how the framerates in the windowed app are handled if they are lower than desktop refresh -- so, if I have a game windowed on my desktop and the desktop if set to refresh at 144 hz while the game is operating at say 100 fps, unless the desktop if matching the games output, I would think you'll get stutter.

    As an experiment for Journey (which has no fullscreen mode), while using G-Sync, I capped the game internally to several values with RTSS -- 141 on a 144 hz monitor resulted in attrocious stuttering constantly despite the RTSS frametime graph being flat -- however, another value I used was refresh rate/2 and this "almost" totally resolved the stuttering (though it still occasionally occurred and any other value I capped to still resulted in weird stuttering). At a glance, I am "guessing" what is going on is what I described above where the desktop continues to refresh at 144 hz so if the game is not matching that output then you get weird judder/stuttering. But, I really don't know for sure, I'm just speculating.
     

  11. aufkrawall2

    aufkrawall2 Master Guru

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    I'd bluntly assume that Nvidia didn't plan the implementation for DWM well enough, as borderless VRR works much better with AMD.
    E.g. it simply didn't work for me without stuttering in BF4 or CS:GO, while it did with AMD the last time I checked.

    Though AMD also have their own kind of issues, e.g. I only need to start and quit Mirror's Edge D3D9 once and desktop DWM seems to be stuck in flickering FreeSync on mode. Perhaps a switch to turn it off for borderless would make it impossible for the desktop to flicker, but such a switch does not even exist in the AMD driver.

    But at least VRR itself works properly with Polaris, which was not the case with my GTX 1070 (sometimes weird brightness flicker and even blanking out). A firmware update improved the situation, but did not fully fix it. I've come to the conclusion that Pascal is not really VRR ready, but at least this issue seems to be fully fixed with Turing (for which I found myself to be forced to send it back due to its goofy fan controls and I can't stand sudden starts of fans spinning...).
     
    Last edited: Aug 5, 2020
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  12. BlindBison

    BlindBison Master Guru

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    @aufkrawall2 Thanks for explaining all of that, it's helpful to know -- I don't know about you, but it really grinds my gears when games release without a true fullscreen exclusive mode. Seems like windowed mode only games can have a lot of bizarre issues in my experience at least with jitter/stuttering, but I'd just assumed that was due to the V-Sync method it uses as described in the V-Sync DF video I referenced above.
     
  13. janos666

    janos666 Master Guru

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    I have similar experience with some Unity Engine based games (which are notorious about lacking FSE mode, sometimes completely, so the command line option isn't available either). It's strange because I tried to put TW3 into windowed mode (actual window, not even borderless) and that seemed to work fine. So, basically, my limited experience is that G-Sync/Windowed only works for games which have FSE mode anyway. LOL.

    The display is (theoretically) synced to the windowed app in focus and everything else outside of that window might stutter (I am not sure if they are synced for some degree, so that N divisible framerates appear without stuttering - one could try playing a 24fps video next to a game capped at 48fps).
     
    Last edited: Aug 5, 2020
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  14. BlindBison

    BlindBison Master Guru

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    @janos666 Thanks! That’s helpful — yeah, it would make sense to me that the window in focus is what the monitor refreshes in sync with. Really interesting about TW3 — I have tried some Unity games like RED AMAZON and noticed some weird judder when using g-sync there.
     
  15. AsiJu

    AsiJu Ancient Guru

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    Unity and its "fullscreen" mode, ugh...

    Bothers me immensely Gsync (fullscreen) won't work with Dusk.
    Not that one really needs VRR in Dusk as it stays pretty much locked to 144 fps and input is snappy with ingame fps cap + ULLM but Gsync would be a notch better still.

    For some reason ingame Vsync must be on too for a smooth image, nv cpl Vsync alone isn't enough.
    Only nv Vsync does enable Vsync but indeed there's strange jitter.

    Tbh I don't know if ULLM either works properly with fake fullscreen but at least pre render limit should be minimized.

    Afaik windowed apps run through DWM compositor so triple buffered vsync of sorts is probably forced on.
    Not sure how much the display driver can override it, if at all?
     
    Last edited: Aug 6, 2020
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  16. janos666

    janos666 Master Guru

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    I wonder about the same and guess it doesn't work (may be doesn't affect pre-render at all either, or simply sets it to 1 since Ultra is supposed to be 1 + fpscap for G-Sync but the cap doesn't seam to work - but then GSync doesn't seem to work either, so...).
    According to BlurBuster's measurements, G-Sync/Windowed theoretically bypasses the compositor but it doesn't seem to be working in recent Win10 builds and/or some game engines (like Unity).
    May be it's the game's fault, may be nVidia should create some special profile for these games.
     
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  17. aufkrawall2

    aufkrawall2 Master Guru

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    Don't want to be fussy, but those quotes aren't by me. :)
     
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  18. CrunchyBiscuit

    CrunchyBiscuit Master Guru

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    Truth.

    Indeed.

    So many developers just use the Unity engine defaults and go with it, completely unaware of the potential issues. I informed and helped out many indie developers with issues related to borderless windowed mode, physics/animation timing issues and frame pacing issues. For every game that gets fixed, three new (broken) ones enter the marketplace. Freck the power of defaults.

    For games based on Unity without an exclusive fullscreen mode, you could try adding "-window-mode exclusive" (without the quotes) as a command line parameter - it forces true (exclusive) fullscreen mode, which might help (some games work completely fine with it, but it doesn't work on certain versions of Unity and might cause issues like stuck loading screens).
     
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  19. evgenim

    evgenim Master Guru

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    Check NVInspector
    Снимок.PNG
     
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  20. AsiJu

    AsiJu Ancient Guru

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    Thanks!

    I tried it with Dusk and it doesn't change anything. If I cap to below refresh the display still stays at 144 Hz and naturally motion becomes choppy.
     
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