AMDGPU's rings VS Radeon's

[Alex Deucher]

On Mon, Aug 11, 2025 at 6:08 PM Alexandre Demers
<alexandre.f.demers at gmail.com> wrote:
>
> Hi,
>
> For those who know, I'm still working on VCE1 enablement under AMDGPU. Progress is happening, slowly but surely. While investigating the ring init calls, a few elements catched my attention and I'd like some help in figuring out the differences between AMDGPU's ring sizes and Radeon's ones.
>
> 1- I understand that the size parameter changed from bytes under radeon_ring_init to dword under amdgpu_ring_init. That being said, some values don't seem to be equivalent between Radeon and AMDGPU. For example, GFX ring size went from 1024 * 1024 bytes to 1024 dwords (for most GFX versions), which seems off even when taking into account how amdgpu_ring_init calculates the final allocated size. This question is more about understanding than a problem strictly speaking.

You can make the ring any size you want.  It's specified in the queue
descriptor.  I don't remember why we picked the sizes we did in radeon
off hand.

>
> 2- Under AMDGPU, SI's GFX (GFX6) ring size is 2048, while this value is 1024 for all the other GFX versions. Under Radeon, the GFX ring size values are all the same (1024 * 1024) under Evergreen/SI/CIK/NI and others. Is there any reason why SI's GFX6 ring size would be twice the size of the other values under AMDGPU?
>

>From the git history:
commit 97041ed37718dc9ba30aa23ca74093dc93ac89fb
Author: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
Date:   Thu Apr 13 16:22:51 2023 +0200

    drm/amdgpu: Increase GFX6 graphics ring size.

    To ensure it supports 192 IBs per submission, so we can keep a
    simplified IB limit in the follow up patch without having to
    look at IP or GPU version.

    Reviewed-by: Christian König <christian.koenig at amd.com>
    Signed-off-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
    Signed-off-by: Alex Deucher <alexander.deucher at amd.com>



> 3- Would it be acceptable to add names to rings under Radeon, the same names as the ones used under AMDGPU? I think it is more talkative for the average user and for debugging purposes to deal with ring names than indexes. I already have patches in my code to address this suggestion.
>

If you think there is value there.  It seems like it would generate a
lot of churn in that driver for little gain.

Alex

> That's all for now.
>
> Cheers
> Alexandre Demers