LFC is broken

Discussion in 'Videocards - NVIDIA GeForce Drivers Section' started by Christizzz, Oct 15, 2020.

  1. Christizzz

    Christizzz New Member

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    So after 2 threads on nvidia and on monitors. and several testing with other users... I can confirm that LFC IS broken on the LG- 27GL850.

    LFC will break after power cycling the screen or waking the screen from sleep.So LFC is Low Frame Compensation... It is a solution for freesync monitors ( gsync compatible monitors) to get smooth experience when the Frames drops below the refresh rate range of the monitor. it is implemented in the driver.

    The LG 27GL850 has range of 48Hz-144Hz

    A practical example like the videos i provided: https://drive.google.com/file/d/14TlVhygd1NYeqcdcZBUz6osWT60EytRT/view?usp=sharing

    another video this time showing tearing https://drive.google.com/file/d/15CoMyzCiHum7Ww6fdorOHYXUq92vXBrf/view?usp=sharing



    When LFC is working correctly:

    • 40FPS will make the screen refresh at 80Hz: smooth and No tearing

    • 50Fps will make the screen refresh at 100Hz: smooth and No tearing

    • 70Fps is already smooth so LFC will disable and the screen will refresh at 70Hz: smooth and No tearing
    When LFC is NOT working correctly ( in this case after power cycling the monitor OR waking the monitor from sleep, the driver of GPU breaks LFC)

    • 40FPS will make the screen refresh all over the place like in my video : Not smooth and visible tearing

    • 50Fps will make the screen refresh at 50Hz: smoothish and No tearing

    • 70Fps will refresh at 70Hz: smooth and No tearing
    you can see that dropping below the 48FPS ( which is the limit of the monitor)..it no longer activate LFC...

    The only way to solve this is to reboot OR to change the refresh rate of the screen from 144 to 120 and then back 144...

    the LFC will be broken again as soon the monitor will power cycle or go to sleep.

    I saw a lot of forums with this problem and thats a freesync + nvidia issue... not specific to my monitor but specific to gsync compatible monitors in general. I confirmed with several users on discord.

    https://www.reddit.com/r/ultrawidemasterrace/comments/ecbw3l/msi_optix_mpg341cqr_g_sync_issues/

    https://forums.eagle.ru/showthread.php?t=230498

    https://www.nvidia.com/en-us/geforc...-dissapears-after-display-sleeps-forced-to-r/





    it doesnt have a lto of coverage because the Gsync will be working but not as intended with the LFC...

    when LFC breaks , stutter and tearing will appear when out of range.



    like in one of the threads, i created a BAT file that cyclce the refresh rate from 144 to 120 and back to 144 in order to reset the LFC and make it work again without rebooting the PC..


    Maybe some users with 10XX can test this if they have a gsync compatible monitor...
    thanks





    regards

    Christian
     
  2. Astyanax

    Astyanax Ancient Guru

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    your linked nvidia thread has nothing to do with LG screens and is content from 6 years ago that should have been locked.....
     
  3. janos666

    janos666 Master Guru

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    G-Sync had LFC ever since it's public release. Only AMD has a name for it because they added it later and had to use some name when referencing it in the change-log as a new feature. But the same rules apply to both. So LFC is not FreeSync / G-Sync Compatible related. It's generic to VRR.

    This is a strange bug you experience but not surprising. Sleep/resume is notorious to cause issues.
     
  4. SalamatiQus

    SalamatiQus Member

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    I have 1080ti with 27GL850 display and I followed on what you did in your first video. Launched pendulum, observed gsync work with all fps presets. After that I turned off and back on monitor and click on each fps preset again but gsync was working correctly with no tearing for me. To add here that was also done on a system that was woken up from hibernation, no cold boot. I also have vsync forced through nvcp.

    27GL850 firmware (if it has anything to do with this issue)
    upload_2020-10-17_13-33-35.png
     

  5. Christizzz

    Christizzz New Member

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    thank you for your reply... fro test purpuse..try to turn vsync off in nvcp...i have the tearing at 40 fps when nvcp is off and this shows that LFC is not working correctyl under 49fps...
    what driver are you using ? latest windows update ? are you running the pendulum at 2560x1440p ?
     
  6. janos666

    janos666 Master Guru

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    LFC does need V-Sync! It's managed by the nVidia driver (at least for Compatible) and it is controlled by V-Sync.
    While G-Sync and V-Sync are both On you get normal V-Sync-like behavior when fps would exceed the VRR range and LFC when it fall below. You get normal "No Sync" behavior wit V-Sync Off and the fps falling below the range. That's by design.
     
  7. Christizzz

    Christizzz New Member

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    Watch my second video... the test where it is working properly doesnt have vsync enabled... 40fps are showing stable 80hz and no tearing... when LFC breaks... 40fps are showing refreah rates all over the place and tearing will appear...in both tests vsync was off

    i do understand this... then why with vsync OFF and the LFC working correctly do i get 80Hz and no tearing at 40fps ? to make it work again ( with VSYNC OFF) change the refresh rate from 144 to 120 and then back to 144... LFC will work correctyl and you wont get tearing at 40fps with Vsync off... because the refresh rate will be 80hz...

    and when LFC will break again ( after power cycling or monitor sleep) 40fps wont show 80hz anymore and tearing will appear if vsync is off ( i do get this)... but LFC IS broken.. doesnt matter if vsync is off or on...

    it is important to check the refresh rate when the pendulum is stable at 40fps... if you are getting 80hz... then LFC is working... and doesnt matter if Vsync is on or off..you wont get tearing...

    if at 40 fps you are not getting 80hz..LFC is not working and teraring will appear under 49FPS if vsync is off
     
    Last edited: Oct 17, 2020
  8. SalamatiQus

    SalamatiQus Member

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    Ok, changed Vsync to "use 3d application settings" and indeed after switching monitor off and on it shows tearing. I can confirm that.

    driver version 456.71
     
  9. SalamatiQus

    SalamatiQus Member

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    janos666 is telling you that what you are seeing is exactly what you should expect when vsync is OFF. Turns out you have to have vsync ON for LFC to function properly, which it did in my first test with vsync ON
     
  10. Christizzz

    Christizzz New Member

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    i do understand this... then why with vsync OFF and the LFC working correctly do i get 80Hz and no tearing at 40fps ? to make it work again ( with VSYNC OFF) change the refresh rate from 144 to 120 and then back to 144... LFC will work correctyl and you wont get tearing at 40fps with Vsync off... because the refresh rate will be 80hz...

    and when LFC will break again ( after power cycling or monitor sleep) 40fps wont show 80hz anymore and tearing will appear if vsync is off ( i do get this)... but LFC IS broken.. doesnt matter if vsync is off or on...

    it is important to check the refresh rate when the pendulum is stable at 40fps... if you are getting 80hz... then LFC is working... and doesnt matter if Vsync is on or off..you wont get tearing...

    if at 40 fps you are not getting 80hz..LFC is not working and teraring will appear under 49FPS if vsync is off
     

  11. SalamatiQus

    SalamatiQus Member

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    It kinda flew over my head that with vsync OFF demo shows working gsync with 40 fps and it breaks after switch monitor off and on, meaning that LFC was working with vsync OFF. However I also noticed that you don't really need to change refresh rate or reboot in order to fix broken LFC in this case, simply exiting fullscreen and reenabling fullscreen back does the same job.

    I guess you only run into this bug in following conditions:
    1. by putting PC to sleep while the game is in fullscreen and is not minimized and then resuming PC back up
    2. if monitor goes to sleep with game running if you leave it unattended for a long time. I am not sure if Windows (or linux systems) lets monitor sleep with a game running even without any input from player for a long period of time.

    i would advice you to fill in bug report but seeing that this bug has 2 workarounds (1 is having Vsync ON which eliminates this problem from happening at all and 2 by reenabling fullscreen or relaunching game) it could be given low priority.
     
    Last edited: Oct 17, 2020
  12. Christizzz

    Christizzz New Member

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    thank you for your reply... 2 things:

    1) so you do confirm that when LFC breaks you also dont get constant 80hz (at 40fps) in your case with the gtx 1080ti ?
    2) no even if i am at the desktop (doesnt matter if i am in a game or not)... and the monitor ( only the monitor ) goes to sleep or get power cycled ( turn off then back on) starting a game with full screen will break LFC...
    3) if LFC is working and i am in a game... minimising the game owill NOT break LFC
    4) there is actually 3 solutions: disable Gsync and then renable gsync in Nvidia Control panel will reset LFC but you will also reset Vsync, reset gpu driver ( pressing Ctrl-Shift-Windows-B) but this will add errors logs in the event viewer of windows, or ( the one i am using and the cleanest and easiet one) i wrote a BAT file that changes the refresh rate from 144 to 120 and then back to 144...this will reset LFC
     
    Last edited: Oct 17, 2020
  13. SalamatiQus

    SalamatiQus Member

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    When LFC breaks I too at first get wild range of Hz reported and then it gets around 60-62 Hz.
    Can you say that reenabling Fullscreen (alt+enter works with demo) fixes LFC for you?
     
  14. Christizzz

    Christizzz New Member

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    the wild Hz at a constant 40fps are the proof that LFC is broken...enabling full screen or minimising the game (or pendulum) doesnt fix it.
    if LFC is broken.. you need to go in nvidia control panel and change the refresh rate from 144 to 120 and then back to 144... then if you try the pendulum you will see constant 80Hz at 40fps... and as i said this will work as long as the monitor doesnt go to sleep or power cycle...
     
  15. SalamatiQus

    SalamatiQus Member

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    Yes, changing refresh rate fixes it but can you please test if simply going out of fullscreen and back fixes it for you too?
     

  16. Christizzz

    Christizzz New Member

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    thanks for your reply...i made an ALT+ENTER ( switch between windowed and full screen) in the pendulum test... it didnt fix the LFC... is this what you meant ?
     
  17. SoLoR

    SoLoR Master Guru

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    I have similar issue with gsync compatible AOC 2590G4 monitor (1080p, 144hz), sometimes (but not always) after monitor goes to sleep I get screen tearing after it wakes up and until today I needed to power cycle the monitor to fix it (or reboot obviously also works), however I just notice changing refresh rate works as well (so thank you for that!). This for me does never happen if whole computer goes to sleep (I have 15min monitor sleep timeout and 1h computer sleep timeout).

    Until today I thought it might be issue with my specific monitor, however its good to know its not :)
     
  18. Christizzz

    Christizzz New Member

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    whats is your GPU ?
     
  19. SoLoR

    SoLoR Master Guru

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    1660TI from MSI, I also have 3 "monitors" connected, 24inch AOC with gsync compat (the one i have issues on), old 24inch 60hz LG monitor and 4K Sharp TV at 60hz with HDR.

    I actually thought maybe it happens because of different monitors with different refresh rates / resolutions... but never got around to test it. But thing is if other people have similar issues, probably this isnt the case...
     
    Last edited: Oct 20, 2020
  20. Christizzz

    Christizzz New Member

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    i dont think it is the same problem..i dont have flicker.... i have problem with LFC... and until now from the reports i got it affect the Pascal cards with gsync compatible monitors...the1660Ti is a Turing card...
    on the other hand... you may want to check the pendulum test and check the refresh rate ( not FPS) value when the tearing appears... if a low FPS value like 40 fps ist not showing 80Hz ( if your monitor has big range)... then you might also have LFC problems
     

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