Any harm in enabling "Resizable Bar" in the BIOS if your GPU doesn't support it yet?

Discussion in 'Videocards - NVIDIA GeForce Drivers Section' started by BlindBison, Apr 17, 2021.

  1. BlindBison

    BlindBison Master Guru

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    I have a 3900X + 2080 Super and my BIOS (latest for ASRock X570 Phantom Gaming 4) does have options under PCEI to enable "4G Decoding Support" (necessary to enable Rebar it seems) and "Resizable Bar" itself.

    Now, at the moment at least (and who knows, maybe forever) 2000 series GPUs do not support Rebar, but -- my thought was, if it didn't hurt anything I could switch it on and maybe down the line if its enabled in the driver on Nvidia's end i'm ready to go.

    That said, I'm also not sure if turning it on for cards that are unsupported would have negative side effects. I did turn it on initially just to check the latest driver for support, but I suppose now I may as well turn it off for the time being if it could cause issues.

    Thoughts? Would there be any advantage in leaving the 4G decoding and/or Rebar enabled or should I just switch them off for now? Thanks!
     
  2. Astyanax

    Astyanax Ancient Guru

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    vulkan stuff will be slower.
     
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  3. SalamatiQus

    SalamatiQus Active Member

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  4. BlindBison

    BlindBison Master Guru

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    Thanks a lot, I’ll just leave it and 4g decoding on the default/off then and just enable PBO as my only change from stock then (I’d read previously that to do that you just move PBO from auto to enabled).

    Much appreciated!
     

  5. BlindBison

    BlindBison Master Guru

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    Thanks, that’s good to know, will leave it off/at default then and just move PBO from auto to enabled as the only change. Much appreciated!
     
  6. Chrysalis

    Chrysalis Master Guru

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    Rebar itself probably no, but above 4g can cause issues with incompatible OS.

    e.g. I noticed my Macrium PE usb boot wont boot if above 4g is enabled.

    Given my other issues and that the games I play have pretty much no performance benefit I am keeping CSM on and above4g/rebar off for now.
     
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  7. artina90

    artina90 Member Guru

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    My X299 motherboard exposes 4G Decoding Support, Resizable Bar and MMIO Granularity.
    I have no idea what I should set MMIO Granularity to with a 2080 Ti.
    Enabling Resizable Bar switches MMIO Granularity to 256G automatically, I have set it to 1G for now.
     
  8. mbk1969

    mbk1969 Ancient Guru

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    I enabled Above 4G option in my x299 BIOS and have no issues.
     
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  9. SalamatiQus

    SalamatiQus Active Member

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    As far as we have observed issue rises on AMD ZEN systems in a similar case like OP has described
     
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  10. skacikpl

    skacikpl Master Guru

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    I did a very quick test on my MSI X570 board with latest beta BIOS and didn't see any significant difference in Serious Sam 4 running vulkan renderer.
    Certainly nothing as severe as 50% performance cut.
     
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  11. BlindBison

    BlindBison Master Guru

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    Thanks all, very good to know -- for now, I've pretty much just turned off the 4G decoding support and turned off Rebar since my machine doesn't support rebar and those were off by default. I haven't done objective testing or anything, but I haven't perceived much of any difference yet. If later down the line rebar is enabled for the 2000 series gpus, then I'll go back in and reenable those settings (since 4g decode is required for rebar it seems).

    Sort of related, for PBO, is that better at "enabled" or "auto" -- in the youtube video for enabling Rebar I'd watched they said that "auto" for PBO (default setting) usually means its off while "enabled" is sort of the "no hassle" way of turning it on so that's what I did. Thanks all,
     
  12. tsunami231

    tsunami231 Ancient Guru

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    Why exactly would enable that stuff have performance hits on card that dont even support it?
     
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  13. BlindBison

    BlindBison Master Guru

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    No clue, hence the initial question haha -- I mean, the default is OFF and if it's not supported I may as well leave it off I suppose. I could leave 4g decode on with rebar off I suppose too.
     
  14. Mineria

    Mineria Ancient Guru

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    I experience no difference in any Vulkan games between it on and off with my 2080S on my up to date Windows 10 install.
     
  15. PrMinisterGR

    PrMinisterGR Ancient Guru

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    I had bad Vulkan performance and Civ 6 would crash for whatever reason.
     

  16. Hog54

    Hog54 Maha Guru

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    I have everything turned off enabling resizable bar even though I have everything to turn it on as in 3070 with bios update but I dont have any of the games that support it.:)
     
  17. MMXMMX

    MMXMMX Member Guru

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    Yes only 3000 series
     

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