Performance for Free: Unlocking Resizable Bar for unsupported AMD GPUs (Polaris, VEGA, Radeon VII)

Discussion in 'Videocards - AMD Radeon Drivers Section' started by Romulus_ut3, Oct 21, 2022.

  1. stitrek

    stitrek New Member

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    GPU:
    RX 470 4gb
    I tested with Rx 470 4gb (Sapphire Nitro+), Ryzen 3600, latest Bios, latest gpu drivers (23.2.1) and also older (22.11.2), resize bar enabled in Bios, above 4g, boot from gpt, CSM disabled.

    In Gpu-z and Device manager it shows that it is enabled and Amd drivers after starting the registry don't work, there is also a registry to turn off, then the Amd drivers work after a PC restart, but the option to turn on SAM inside the driver disappears.

    It is also tested with DDU and both 22.11.2 and 23.2.2 Amd drivers on both Win 10 and 11, it is all the same.
     
    Last edited: Feb 22, 2023
  2. stitrek

    stitrek New Member

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    GPU:
    RX 470 4gb
    I tested more, with Ryzen 3600 and Rx 470 4gb, this registry is making Amd Adrenaline drivers not to work
    KMD_EnableReBarForLegacyASIC"=dword:00000001

    With this two registry Amd adrenaline works but still Resizable Bar Not Available
    KMD_RebarControlMode"=dword:00000001
    KMD_RebarControlSupport"=dword:00000001
    Gpuz.gif Gpuz2.gif
     
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  3. Have there been any tests with Above 4G Decode enabled, but resizable BAR disabled?

    There's this Reddit thread that details on Linux that on some boards (seemingly Gigabyte mostly?) or set-ups, enabling resizable BAR lowers performance, but having just above 4G Decode enabled and allowing the kernel to do the BAR resize gives the best performance.

    On Linux with AMDGPU it resizes the BAR from 256M to the VRAM size later in the boot process if resizable BAR is disabled. It starts with the full VRAM size BAR if resizable BAR is enabled. I suspect the BAR could be placed somewhere non-ideally depending on if the OS or BIOS does it? And iirc, Windows by itself doesn't do any kind of BAR resizing?
     
  4. katapaltes

    katapaltes Member

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    GPU:
    RX 470
    Hi @Vlad00n , There may be enough address space below 4G on your motherboard to enable 1GB of BAR without even enabling Above 4G. That was the case with my Gigabyte and Dell Ivy/Sandy Bridge motherboards. You would need to add ReBarDxe.ffs to the BIOS (UEFI) and reflash it, run RebarState.exe with no more than 1024MB, and add the three registry edits *to the correct registry path* (ending in either "0000" or "0001" depending on your setup). That's a lot less work than doing the Above 4G stuff along with any suggested DSDT mods. I was eventually able to get Above 4G on my motherboards working, but I was never able to get the computer to boot with anything more than 2GB BAR enabled after many hours of trying.

    My posts are on the Intel thread for this topic at https://forums.guru3d.com/threads/r...n-intels-3rd-gen-ivy-bridge-from-2012.445040/

    As for a guide, I just followed the applicable pages at https://github.com/xCuri0/ReBarUEFI/releases
     

  5. zingzs

    zingzs Maha Guru

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    GPU:
    Sapphire 6700XT 12G
    For specific Gigabyte AMD Motherboards, you need to mod the BIOS in order to activate Resizeable BAR, because some of AMD Ryzen Processors won't allow to activate ReBAR by native (in my case I'm using Gigabyte B450M Gaming + Ryzen 5 3400G which doesn't have ReBAR option due to processor limitation, so I need to use modded BIOS)
    ReBAR_SAM3400G.png
     
  6. dieguete0

    dieguete0 Member

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    GPU:
    RX 6600 Eagle 8G
    I don't know if I'm doing something wrong, BAR doesn't work for me in any way in AB350Gaming and R5 1600AF and RX580Nitro 4g ELPIDA. Could you explain the bios changes please.
    This is what I modify from the Bios to show BAR in two different instances.
    or simply with my components it doesn't work.

    The active and performance falls very much.
    What seems strange to me is that I read that people with older teams come to activate and it works as expected.
    Greetings.
     

    Attached Files:

    Last edited: Mar 4, 2023
  7. zingzs

    zingzs Maha Guru

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    GPU:
    Sapphire 6700XT 12G
    4GB GPU cards must use 2GB ReBAR size (equivalent to 2048MB) afaik
    If you need more assistance, you can DM this guy @Koekieezzz .
    I got helped by him to make my motherboard able to use ReBAR for Navi 2X GPUs, it is known that Gigabyte hides the ReBAR feature for my CPU 3400G in my motherboard (including Zen and Zen+), I can only guarantee this trick for my motherboard

    Edit : Your trick only works for motherboard that uses AMI APTIO Version 4, so it won't work for you that uses AMI APTIO Version 5 or higher. Needs very specific modding method that is extremely difficult rather than just add new modules, and ofc with live teamviewer or similar to teach that
     
    Last edited: Mar 4, 2023
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  8. dieguete0

    dieguete0 Member

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    GPU:
    RX 6600 Eagle 8G
    Edit : Your trick only works for motherboard that uses AMI APTIO Version 4, so it won't work for you that uses AMI APTIO Version 5. Needs very specific modding method that is extremely difficult rather than just add new modules, and ofc with live teamviewer or similar to teach that[/QUOTE]

    Ok, thank you, I tried with all values from 9=512 10=1024 11=2048 12=4096 etc.
    It's not a problem of displaying it, we think it's a problem in the memory range that creates it. It has a very high latency.
    Although I don't know what to think anymore, I even mutated the board to a B450 Pro with the same result. Thanks again.
     
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  9. zingzs

    zingzs Maha Guru

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    GPU:
    Sapphire 6700XT 12G
    no problem, I'm a newbie for this thing so that's it
     
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  10. Koekieezzz

    Koekieezzz New Member

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    GPU:
    Palit RTX 3060Ti 8G
    do u have the access to flash a modded bios by any means? if so, which bios do you want to use and which ver?
     
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  11. Koekieezzz

    Koekieezzz New Member

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    GPU:
    Palit RTX 3060Ti 8G
    {Deleted}
     
  12. dieguete0

    dieguete0 Member

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    GPU:
    RX 6600 Eagle 8G
    YES I can install a bios that is modified , This is modified by me changes for startup fans, remove savings, unlock MMIO, add ReBarUEFI etc ...
    AB350G.51h this is mod , Bar is disabled since it didn't work for me. Thank you very much
    https://mega.nz/file/1UMyhADb#Cq4K_cGicLj3yFE-SXAHvYog4cV4Fsn1t-uihMGSjQ8
     
    Last edited: Mar 4, 2023
  13. Koekieezzz

    Koekieezzz New Member

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    GPU:
    Palit RTX 3060Ti 8G
    Here you go, just flash it, enable above 4g decoding in bios (is a must), disable CSM, boot to windows, then use rebarstate as admin and set it to 11 (if your card is 2GB), or 32 if your card is 8GB

    https://drive.google.com/file/d/1Ik2y2IIc5LAdhKA2LU0xyK2aIAJ-NU5T/view?usp=share_link
     
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  14. dieguete0

    dieguete0 Member

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    GPU:
    RX 6600 Eagle 8G
  15. Koekieezzz

    Koekieezzz New Member

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    GPU:
    Palit RTX 3060Ti 8G

  16. dieguete0

    dieguete0 Member

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    GPU:
    RX 6600 Eagle 8G
    Sorry, I have a family eating and I haven't been able to test all the config (when they leave I'll try or stop and I'll tell you), at the moment Legacy behaves the same, What exactly did you touch? Very Thanks
     
  17. Koekieezzz

    Koekieezzz New Member

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    GPU:
    Palit RTX 3060Ti 8G
    just placing rebardxe.ffs on the bottom most dxe driver using mmtool.
     
  18. dieguete0

    dieguete0 Member

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    GPU:
    RX 6600 Eagle 8G

    Attached Files:

    Last edited: Mar 4, 2023
  19. dieguete0

    dieguete0 Member

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    GPU:
    RX 6600 Eagle 8G
    @Koekieezzz
    Muchas gracias por vuestra ayuda, aunque sigo igual, he probado todas las combinaciones que se me han ocurrido y no cambia nada.
    Gracias de nuevo y saludos.
     
  20. zingzs

    zingzs Maha Guru

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