Resizeable BAR support issues

Discussion in 'Videocards - AMD Radeon Drivers Section' started by Espionage724, Nov 26, 2020.

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  1. JonasBeckman

    JonasBeckman Ancient Guru

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    https://www.reddit.com/r/Amd/comments/krkyva/hardware_unboxed_amds_killer_feature_sam_36_game/

    Hardware unboxed testing and also this user quote. :)

    Found it interesting and thus the performance decreases could be from early testing and bios bugs. :)

    And of interest is that it's overall nothing too complicated so unless AMD intentionally did something more with SAM it should just work however it's currently (maybe?) only supported for the 6000 series GPU's though motherboard and CPU wise it's now looking better.

    Just need that 1.1.9.0 AGESA and those fixes over 1.0.0.0 or 1.0.8.0 for overall system improvements and stability. :D
    (Slowly rolling out though.)



    EDIT: Should also mean this can carry right over with the same benefits on Intel CPU's and NVIDIA GPU's hopefully without any complications in the process.
    Should be fine though, seems like it just affected performance anyway and less of a stability issue.

    EDIT:
    Interesting as well on how this works and benefits and possible cases where it won't do much like the last part of that quote.

     
    Last edited: Jan 7, 2021
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  2. Astyanax

    Astyanax Ancient Guru

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    Resizeable bar is a requirement of DirectStorage :D
     
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  3. Espionage724

    Espionage724 Member Guru

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    What's the actual relationship with above 4G decode and Resizable BAR?

    From what I can see with Linux, with just above 4G decode, it starts out with a 256M BAR, and then some part of the kernel (I think a pcie or amdgpu module) re-sizes it later to the full VRAM size (8G). With resizable BAR enabled, Linux immediately starts with the full VRAM size for the BAR, which makes me assume that the BAR gets set via the firmware and Linux just uses it. Is this correct?

    I don't quite know what Windows does with just above 4G decode, but games and things still work. With resizable BAR enabled, VRAM reporting breaks with AMD's Radeon control panel (both Task Manager and GPU-Z report VRAM usage still), and games either flicker and don't render at all, or run significantly slower. But apparently this only affects some GPU architectures? I've heard someone with Navi being able to use Resizable BAR with 20.11.1 drivers fine, but I'm not sure on what they all tested.

    I don't know if my BIOS is affected by that "They accidentally removed the window change without expanding the addressable area" note (PRIME X470-PRO, 5809), but if it was, wouldn't Linux be broken as well?

    Other game reports (RX 580, 20.Q3, re-size BAR enabled):
    • Path of Exile DX11: Works
    • Path of Exile Vulkan: Broken (low FPS, max GPU usage)
    • Guild Wars 2 DX9: Broken (low FPS, max GPU usage)
    • Guild Wars 2 Vulkan (DXVK): Broken (black/white flicker)
    • Guild Wars 2 DX12 (d912pxy): Broken (crash on start-up)
    • Blade & Sorcery (likely DX11): Works
    • SteamVR: Works
    • Oculus Dash: Broken (low FPS, max GPU usage; spam of GPU encoder backed-up)
    Generally, it looks like anything using DX11 is fine, while other graphics APIs (DX9, DX12, Vulkan) either run too slow or don't work in any usable manner.
     
    Last edited: Jan 8, 2021
  4. Astyanax

    Astyanax Ancient Guru

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    You can't perform a 8GB transfer from system mem to graphics mem without being able to map that 8GB's of device memory.

    Windows by default (and prior to uefi) can only map video device memory below the 4GB address space.
     
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  5. Espionage724

    Espionage724 Member Guru

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    Can Windows by itself map video memory above 4GB address space with just the above 4G decode BIOS/firmware option (with UEFI)? Or does this have to be explicitly enable by the graphics driver?
     
  6. Astyanax

    Astyanax Ancient Guru

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    There are aspects of the Windows Kernel and how you configure its device drivers that are entirely under NDA, or simply not publicized at all,

    The driver itself has to identify itself as supporting Resizable Bar so that on boot the Large Range (to the maximum size of the memory on the device) is exposed as addressable, this is usually done at device init using a registry key that enables the capability (like MSIs, msi channels etc)

    You need to be a SIG member to be able to log in and view the documentation for Resizable bar too :\
     
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  7. user1

    user1 Ancient Guru

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    Last edited: Jan 8, 2021
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  8. PhazDelta

    PhazDelta Member Guru

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    asus tuf gaming plus X470 lastest bios Support resizeable bar work great on my 5 2600

    [​IMG]
     
  9. mikeysg

    mikeysg Ancient Guru

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    I think GB just released its final/stable BIOS for my X570 mobo, F31, which I've installed. Like the beta F31q I had before the update, above 4G Decoding (Enabled) and Resize Bar (Auto) options are available much like the Asus one above.
     
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  10. Espionage724

    Espionage724 Member Guru

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    Checked for BIOS updates on my X470-PRO and just noticed there's a 5821 beta now (Jan 8th) with AM4 AGESA V2 PI 1.1.9.0.

    Edit: The graphics driver version matters. Seemingly Resizable BAR works fine on my RX 580 with 20.12.1 (latest Adrenaline), but it goes back to broken VRAM reporting with 20.Q4 (latest Enterprise; slightly older than 20.11.1).

    With 20.12.1 (latest Adrenaline currently), VRAM usage is reported correctly from Radeon Control Panel (not "Infinity"). Guild Wars 2 (DX12 d912pxy) and Path of Exile (Vulkan) work fine too.

    I have Large Memory Range as well (RX 580, 2700X, Above 4G and Re-Sizable BAR enabled):

    [​IMG]
     
    Last edited: Jan 11, 2021

  11. Undying

    Undying Ancient Guru

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    Disabled csm, enabled 4G but still no resize bar option latest f31 from gigabyte.

    [​IMG]
     
  12. PhazDelta

    PhazDelta Member Guru

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    Put csm auto i have same probleme when i put csm disable it not work .
     
  13. Undying

    Undying Ancient Guru

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    There is only option to enable and disable.
     
  14. GSDragoon

    GSDragoon Master Guru

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    I just updated to F31 yesterday and it was showing up for me. I did the who reset to defaults, shut down, cut power for a minute, turn back on and reset to defaults again. Using 3900x, X570 Aorus Master and RX 6800.
     
  15. Undying

    Undying Ancient Guru

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    well in this case its 2700x and rx580 so could be some compability issue in this case, who knows.
     

  16. Chastity

    Chastity Ancient Guru

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    RBAR gave my system today a nasty. Machine booting to a black screen, and nicely occurring while I am doing a CU update. Disabled and system started up fine.

    20.12.1 + 1190 AGESA. I understand 1200 is around the corner.
     
  17. DanielRX

    DanielRX Active Member

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    RBAR gave my system today a Machine booting to a black screen, (Ryzen5 1600 + RX Vega56)
    I disabled and system started up fine!

    (black screen only ocurring at cold boot, beeps Motherboard 1 long, 3 short)

    1.2.0.0 AGESA.date: 18/01/2021.

    PRIME B450M-GAMING/BR BIOS 2803
     
    Last edited: Jan 19, 2021
  18. JonasBeckman

    JonasBeckman Ancient Guru

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    I don't think Zen1 gains too much from it but that could have changed not sure about Zen+ either and then Zen2 and Zen3 are showing gains and supports this long as the various settings and the disk driver and all also follow in having support here for UEFI without compatibility support module / CSM active.

    Curious error there too, motherboard manual might have the error code or beep code for what that actually means.
    Not booting up after passing the bios screen or logo might be the OS file system from a older drive or setup but if it refuses to start up at all without a CMOS clear and keeping the option disabled it's something else.


    EDIT: There's a bunch of stuff for it, activating Above 4G as one requirement or if activating ReBAR that might then might toggle this 4G setting and since it's required could also disable CSM so you need those two other settings to work as well.
     
    Last edited: Jan 19, 2021
  19. suty455

    suty455 Master Guru

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    would be nice if Nvidia pulled out its finger and enabled it, did they not say it was an easy fix and just needed a friver update to sort, the delay seems to suggest that is not the case
     
  20. Astyanax

    Astyanax Ancient Guru

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    they could release a driver, but only the 3060 would have ReBar working.
     

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